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* [PATCH v17 0/9] mm / virtio: Provide support for free page reporting
@ 2020-02-11 22:45 Alexander Duyck
  2020-02-11 22:46 ` [PATCH v17 1/9] mm: Adjust shuffle code to allow for future coalescing Alexander Duyck
                   ` (13 more replies)
  0 siblings, 14 replies; 29+ messages in thread
From: Alexander Duyck @ 2020-02-11 22:45 UTC (permalink / raw)
  To: kvm, david, mst, linux-kernel, linux-mm, akpm, mgorman
  Cc: yang.zhang.wz, pagupta, konrad.wilk, nitesh, riel, willy,
	lcapitulino, dave.hansen, wei.w.wang, aarcange, pbonzini,
	dan.j.williams, mhocko, alexander.h.duyck, vbabka, osalvador

This series provides an asynchronous means of reporting free guest pages
to a hypervisor so that the memory associated with those pages can be
dropped and reused by other processes and/or guests on the host. Using
this it is possible to avoid unnecessary I/O to disk and greatly improve
performance in the case of memory overcommit on the host.

When enabled we will be performing a scan of free memory every 2 seconds
while pages of sufficiently high order are being freed. In each pass at
least one sixteenth of each free list will be reported. By doing this we
avoid racing against other threads that may be causing a high amount of
memory churn.

The lowest page order currently scanned when reporting pages is
pageblock_order so that this feature will not interfere with the use of
Transparent Huge Pages in the case of virtualization.

Currently this is only in use by virtio-balloon however there is the hope
that at some point in the future other hypervisors might be able to make
use of it. In the virtio-balloon/QEMU implementation the hypervisor is
currently using MADV_DONTNEED to indicate to the host kernel that the page
is currently free. It will be zeroed and faulted back into the guest the
next time the page is accessed.

To track if a page is reported or not the Uptodate flag was repurposed and
used as a Reported flag for Buddy pages. We walk though the free list
isolating pages and adding them to the scatterlist until we either
encounter the end of the list or have processed at least one sixteenth of
the pages that were listed in nr_free prior to us starting. If we fill the
scatterlist before we reach the end of the list we rotate the list so that
the first unreported page we encounter is moved to the head of the list as
that is where we will resume after we have freed the reported pages back
into the tail of the list.

Below are the results from various benchmarks. I primarily focused on two
tests. The first is the will-it-scale/page_fault2 test, and the other is
a modified version of will-it-scale/page_fault1 that was enabled to use
THP. I did this as it allows for better visibility into different parts
of the memory subsystem. The guest is running with 32G for RAM on one
node of a E5-2630 v3. The host has had some features such as CPU turbo
disabled in the BIOS.

Test                   page_fault1 (THP)    page_fault2
Name            tasks  Process Iter  STDEV  Process Iter  STDEV
Baseline            1    1012402.50  0.14%     361855.25  0.81%
                   16    8827457.25  0.09%    3282347.00  0.34%

Patches Applied     1    1007897.00  0.23%     361887.00  0.26%
                   16    8784741.75  0.39%    3240669.25  0.48%

Patches Enabled     1    1010227.50  0.39%     359749.25  0.56%
                   16    8756219.00  0.24%    3226608.75  0.97%

Patches Enabled     1    1050982.00  4.26%     357966.25  0.14%
 page shuffle      16    8672601.25  0.49%    3223177.75  0.40%

Patches enabled     1    1003238.00  0.22%     360211.00  0.22%
 shuffle w/ RFC    16    8767010.50  0.32%    3199874.00  0.71%

The results above are for a baseline with a linux-next-20191219 kernel,
that kernel with this patch set applied but page reporting disabled in
virtio-balloon, the patches applied and page reporting fully enabled, the
patches enabled with page shuffling enabled, and the patches applied with
page shuffling enabled and an RFC patch that makes used of MADV_FREE in
QEMU. These results include the deviation seen between the average value
reported here versus the high and/or low value. I observed that during the
test memory usage for the first three tests never dropped whereas with the
patches fully enabled the VM would drop to using only a few GB of the
host's memory when switching from memhog to page fault tests.

Any of the overhead visible with this patch set enabled seems due to page
faults caused by accessing the reported pages and the host zeroing the page
before giving it back to the guest. This overhead is much more visible when
using THP than with standard 4K pages. In addition page shuffling seemed to
increase the amount of faults generated due to an increase in memory churn.
The overehad is reduced when using MADV_FREE as we can avoid the extra
zeroing of the pages when they are reintroduced to the host, as can be seen
when the RFC is applied with shuffling enabled.

The overall guest size is kept fairly small to only a few GB while the test
is running. If the host memory were oversubscribed this patch set should
result in a performance improvement as swapping memory in the host can be
avoided.

A brief history on the background of free page reporting can be found at:
https://lore.kernel.org/lkml/29f43d5796feed0dec8e8bb98b187d9dac03b900.camel@linux.intel.com/

Changes from v14:
https://lore.kernel.org/lkml/20191119214454.24996.66289.stgit@localhost.localdomain/
Renamed "unused page reporting" to "free page reporting"
  Updated code, kconfig, and patch descriptions
Split out patch for __free_isolated_page
  Renamed function to __putback_isolated_page
Rewrote core reporting functionality
  Added logic to reschedule worker in 2 seconds instead of run to completion
  Removed reported_pages statistics
  Removed REPORTING_REQUESTED bit used in zone flags
  Replaced page_reporting_dev_info refcount with state variable
  Removed scatterlist from page_reporting_dev_info
  Removed capacity from page reporting device
  Added dynamic scatterlist allocation/free at start/end of reporting process
  Updated __free_one_page so that reported pages are not always added to tail
  Added logic to handle error from report function
Updated virtio-balloon patch that adds support for page reporting
  Updated patch description to try and highlight differences in approaches
  Updated logic to reflect that we cannot limit the scatterlist from device
  Added logic to return error from report function
Moved documentation patch to end of patch set

Changes from v15:
https://lore.kernel.org/lkml/20191205161928.19548.41654.stgit@localhost.localdomain/
Rebased on linux-next-20191219
Split out patches for budget and moving head to last page processed
Updated budget code to reduce how much memory is reported per pass
Added logic to also rotate the list if we exit due a page isolation failure
Added migratetype as argument in __putback_isolated_page

Changes from v16:
https://lore.kernel.org/lkml/20200103210509.29237.18426.stgit@localhost.localdomain/
Rebased on linux-next-20200122
  Updated patch 2 to to account for removal of pr_info in __isolate_free_page 
Updated patch title for patches 7, 8, and 9 to included mm/page_reporting

Changes from v16.1:
https://lore.kernel.org/lkml/20200122173040.6142.39116.stgit@localhost.localdomain/
Rebased QEMU patches to latest
Rebased on linux-next-20200211
  Tweaked cover page to more accurately describe hinting process
  Verified results have not changed in significant way

---

Alexander Duyck (9):
      mm: Adjust shuffle code to allow for future coalescing
      mm: Use zone and order instead of free area in free_list manipulators
      mm: Add function __putback_isolated_page
      mm: Introduce Reported pages
      virtio-balloon: Pull page poisoning config out of free page hinting
      virtio-balloon: Add support for providing free page reports to host
      mm/page_reporting: Rotate reported pages to the tail of the list
      mm/page_reporting: Add budget limit on how many pages can be reported per pass
      mm/page_reporting: Add free page reporting documentation


 Documentation/vm/free_page_reporting.rst |   41 +++
 drivers/virtio/Kconfig                   |    1 
 drivers/virtio/virtio_balloon.c          |   87 +++++++
 include/linux/mmzone.h                   |   44 ----
 include/linux/page-flags.h               |   11 +
 include/linux/page_reporting.h           |   26 ++
 include/uapi/linux/virtio_balloon.h      |    1 
 mm/Kconfig                               |   11 +
 mm/Makefile                              |    1 
 mm/internal.h                            |    2 
 mm/page_alloc.c                          |  164 ++++++++++----
 mm/page_isolation.c                      |    6 
 mm/page_reporting.c                      |  364 ++++++++++++++++++++++++++++++
 mm/page_reporting.h                      |   54 ++++
 mm/shuffle.c                             |   12 -
 mm/shuffle.h                             |    6 
 16 files changed, 725 insertions(+), 106 deletions(-)
 create mode 100644 Documentation/vm/free_page_reporting.rst
 create mode 100644 include/linux/page_reporting.h
 create mode 100644 mm/page_reporting.c
 create mode 100644 mm/page_reporting.h

--

^ permalink raw reply	[flat|nested] 29+ messages in thread

* [PATCH v17 1/9] mm: Adjust shuffle code to allow for future coalescing
  2020-02-11 22:45 [PATCH v17 0/9] mm / virtio: Provide support for free page reporting Alexander Duyck
@ 2020-02-11 22:46 ` Alexander Duyck
  2020-02-11 22:46 ` [PATCH v17 2/9] mm: Use zone and order instead of free area in free_list manipulators Alexander Duyck
                   ` (12 subsequent siblings)
  13 siblings, 0 replies; 29+ messages in thread
From: Alexander Duyck @ 2020-02-11 22:46 UTC (permalink / raw)
  To: kvm, david, mst, linux-kernel, linux-mm, akpm, mgorman
  Cc: yang.zhang.wz, pagupta, konrad.wilk, nitesh, riel, willy,
	lcapitulino, dave.hansen, wei.w.wang, aarcange, pbonzini,
	dan.j.williams, mhocko, alexander.h.duyck, vbabka, osalvador

From: Alexander Duyck <alexander.h.duyck@linux.intel.com>

Move the head/tail adding logic out of the shuffle code and into the
__free_one_page function since ultimately that is where it is really
needed anyway. By doing this we should be able to reduce the overhead
and can consolidate all of the list addition bits in one spot.

Acked-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
---
 include/linux/mmzone.h |   12 --------
 mm/page_alloc.c        |   71 ++++++++++++++++++++++++++++--------------------
 mm/shuffle.c           |   12 ++++----
 mm/shuffle.h           |    6 ++++
 4 files changed, 54 insertions(+), 47 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 462f6873905a..bdcd071ab67f 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -116,18 +116,6 @@ static inline void add_to_free_area_tail(struct page *page, struct free_area *ar
 	area->nr_free++;
 }
 
-#ifdef CONFIG_SHUFFLE_PAGE_ALLOCATOR
-/* Used to preserve page allocation order entropy */
-void add_to_free_area_random(struct page *page, struct free_area *area,
-		int migratetype);
-#else
-static inline void add_to_free_area_random(struct page *page,
-		struct free_area *area, int migratetype)
-{
-	add_to_free_area(page, area, migratetype);
-}
-#endif
-
 /* Used for pages which are on another list */
 static inline void move_to_free_area(struct page *page, struct free_area *area,
 			     int migratetype)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3c4eb750a199..bf36cdfea07a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -871,6 +871,36 @@ static inline struct capture_control *task_capc(struct zone *zone)
 #endif /* CONFIG_COMPACTION */
 
 /*
+ * If this is not the largest possible page, check if the buddy
+ * of the next-highest order is free. If it is, it's possible
+ * that pages are being freed that will coalesce soon. In case,
+ * that is happening, add the free page to the tail of the list
+ * so it's less likely to be used soon and more likely to be merged
+ * as a higher order page
+ */
+static inline bool
+buddy_merge_likely(unsigned long pfn, unsigned long buddy_pfn,
+		   struct page *page, unsigned int order)
+{
+	struct page *higher_page, *higher_buddy;
+	unsigned long combined_pfn;
+
+	if (order >= MAX_ORDER - 2)
+		return false;
+
+	if (!pfn_valid_within(buddy_pfn))
+		return false;
+
+	combined_pfn = buddy_pfn & pfn;
+	higher_page = page + (combined_pfn - pfn);
+	buddy_pfn = __find_buddy_pfn(combined_pfn, order + 1);
+	higher_buddy = higher_page + (buddy_pfn - combined_pfn);
+
+	return pfn_valid_within(buddy_pfn) &&
+	       page_is_buddy(higher_page, higher_buddy, order + 1);
+}
+
+/*
  * Freeing function for a buddy system allocator.
  *
  * The concept of a buddy system is to maintain direct-mapped table
@@ -899,11 +929,13 @@ static inline void __free_one_page(struct page *page,
 		struct zone *zone, unsigned int order,
 		int migratetype)
 {
-	unsigned long combined_pfn;
+	struct capture_control *capc = task_capc(zone);
 	unsigned long uninitialized_var(buddy_pfn);
-	struct page *buddy;
+	unsigned long combined_pfn;
+	struct free_area *area;
 	unsigned int max_order;
-	struct capture_control *capc = task_capc(zone);
+	struct page *buddy;
+	bool to_tail;
 
 	max_order = min_t(unsigned int, MAX_ORDER, pageblock_order + 1);
 
@@ -972,35 +1004,16 @@ static inline void __free_one_page(struct page *page,
 done_merging:
 	set_page_order(page, order);
 
-	/*
-	 * If this is not the largest possible page, check if the buddy
-	 * of the next-highest order is free. If it is, it's possible
-	 * that pages are being freed that will coalesce soon. In case,
-	 * that is happening, add the free page to the tail of the list
-	 * so it's less likely to be used soon and more likely to be merged
-	 * as a higher order page
-	 */
-	if ((order < MAX_ORDER-2) && pfn_valid_within(buddy_pfn)
-			&& !is_shuffle_order(order)) {
-		struct page *higher_page, *higher_buddy;
-		combined_pfn = buddy_pfn & pfn;
-		higher_page = page + (combined_pfn - pfn);
-		buddy_pfn = __find_buddy_pfn(combined_pfn, order + 1);
-		higher_buddy = higher_page + (buddy_pfn - combined_pfn);
-		if (pfn_valid_within(buddy_pfn) &&
-		    page_is_buddy(higher_page, higher_buddy, order + 1)) {
-			add_to_free_area_tail(page, &zone->free_area[order],
-					      migratetype);
-			return;
-		}
-	}
-
+	area = &zone->free_area[order];
 	if (is_shuffle_order(order))
-		add_to_free_area_random(page, &zone->free_area[order],
-				migratetype);
+		to_tail = shuffle_pick_tail();
 	else
-		add_to_free_area(page, &zone->free_area[order], migratetype);
+		to_tail = buddy_merge_likely(pfn, buddy_pfn, page, order);
 
+	if (to_tail)
+		add_to_free_area_tail(page, area, migratetype);
+	else
+		add_to_free_area(page, area, migratetype);
 }
 
 /*
diff --git a/mm/shuffle.c b/mm/shuffle.c
index b3fe97fd6654..e65d57f39486 100644
--- a/mm/shuffle.c
+++ b/mm/shuffle.c
@@ -183,11 +183,11 @@ void __meminit __shuffle_free_memory(pg_data_t *pgdat)
 		shuffle_zone(z);
 }
 
-void add_to_free_area_random(struct page *page, struct free_area *area,
-		int migratetype)
+bool shuffle_pick_tail(void)
 {
 	static u64 rand;
 	static u8 rand_bits;
+	bool ret;
 
 	/*
 	 * The lack of locking is deliberate. If 2 threads race to
@@ -198,10 +198,10 @@ void add_to_free_area_random(struct page *page, struct free_area *area,
 		rand = get_random_u64();
 	}
 
-	if (rand & 1)
-		add_to_free_area(page, area, migratetype);
-	else
-		add_to_free_area_tail(page, area, migratetype);
+	ret = rand & 1;
+
 	rand_bits--;
 	rand >>= 1;
+
+	return ret;
 }
diff --git a/mm/shuffle.h b/mm/shuffle.h
index 777a257a0d2f..4d79f03b6658 100644
--- a/mm/shuffle.h
+++ b/mm/shuffle.h
@@ -22,6 +22,7 @@ enum mm_shuffle_ctl {
 DECLARE_STATIC_KEY_FALSE(page_alloc_shuffle_key);
 extern void page_alloc_shuffle(enum mm_shuffle_ctl ctl);
 extern void __shuffle_free_memory(pg_data_t *pgdat);
+extern bool shuffle_pick_tail(void);
 static inline void shuffle_free_memory(pg_data_t *pgdat)
 {
 	if (!static_branch_unlikely(&page_alloc_shuffle_key))
@@ -44,6 +45,11 @@ static inline bool is_shuffle_order(int order)
 	return order >= SHUFFLE_ORDER;
 }
 #else
+static inline bool shuffle_pick_tail(void)
+{
+	return false;
+}
+
 static inline void shuffle_free_memory(pg_data_t *pgdat)
 {
 }


^ permalink raw reply	[flat|nested] 29+ messages in thread

* [PATCH v17 2/9] mm: Use zone and order instead of free area in free_list manipulators
  2020-02-11 22:45 [PATCH v17 0/9] mm / virtio: Provide support for free page reporting Alexander Duyck
  2020-02-11 22:46 ` [PATCH v17 1/9] mm: Adjust shuffle code to allow for future coalescing Alexander Duyck
@ 2020-02-11 22:46 ` Alexander Duyck
  2020-02-11 22:46 ` [PATCH v17 3/9] mm: Add function __putback_isolated_page Alexander Duyck
                   ` (11 subsequent siblings)
  13 siblings, 0 replies; 29+ messages in thread
From: Alexander Duyck @ 2020-02-11 22:46 UTC (permalink / raw)
  To: kvm, david, mst, linux-kernel, linux-mm, akpm, mgorman
  Cc: yang.zhang.wz, pagupta, konrad.wilk, nitesh, riel, willy,
	lcapitulino, dave.hansen, wei.w.wang, aarcange, pbonzini,
	dan.j.williams, mhocko, alexander.h.duyck, vbabka, osalvador

From: Alexander Duyck <alexander.h.duyck@linux.intel.com>

In order to enable the use of the zone from the list manipulator functions
I will need access to the zone pointer. As it turns out most of the
accessors were always just being directly passed &zone->free_area[order]
anyway so it would make sense to just fold that into the function itself
and pass the zone and order as arguments instead of the free area.

In order to be able to reference the zone we need to move the declaration
of the functions down so that we have the zone defined before we define the
list manipulation functions. Since the functions are only used in the file
mm/page_alloc.c we can just move them there to reduce noise in the header.

Acked-by: Mel Gorman <mgorman@techsingularity.net>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Pankaj Gupta <pagupta@redhat.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
---
 include/linux/mmzone.h |   32 -----------------------
 mm/page_alloc.c        |   67 +++++++++++++++++++++++++++++++++++-------------
 2 files changed, 49 insertions(+), 50 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index bdcd071ab67f..a32bd503b9fc 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -100,29 +100,6 @@ struct free_area {
 	unsigned long		nr_free;
 };
 
-/* Used for pages not on another list */
-static inline void add_to_free_area(struct page *page, struct free_area *area,
-			     int migratetype)
-{
-	list_add(&page->lru, &area->free_list[migratetype]);
-	area->nr_free++;
-}
-
-/* Used for pages not on another list */
-static inline void add_to_free_area_tail(struct page *page, struct free_area *area,
-				  int migratetype)
-{
-	list_add_tail(&page->lru, &area->free_list[migratetype]);
-	area->nr_free++;
-}
-
-/* Used for pages which are on another list */
-static inline void move_to_free_area(struct page *page, struct free_area *area,
-			     int migratetype)
-{
-	list_move(&page->lru, &area->free_list[migratetype]);
-}
-
 static inline struct page *get_page_from_free_area(struct free_area *area,
 					    int migratetype)
 {
@@ -130,15 +107,6 @@ static inline struct page *get_page_from_free_area(struct free_area *area,
 					struct page, lru);
 }
 
-static inline void del_page_from_free_area(struct page *page,
-		struct free_area *area)
-{
-	list_del(&page->lru);
-	__ClearPageBuddy(page);
-	set_page_private(page, 0);
-	area->nr_free--;
-}
-
 static inline bool free_area_empty(struct free_area *area, int migratetype)
 {
 	return list_empty(&area->free_list[migratetype]);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index bf36cdfea07a..de916aa06a27 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -870,6 +870,44 @@ static inline struct capture_control *task_capc(struct zone *zone)
 }
 #endif /* CONFIG_COMPACTION */
 
+/* Used for pages not on another list */
+static inline void add_to_free_list(struct page *page, struct zone *zone,
+				    unsigned int order, int migratetype)
+{
+	struct free_area *area = &zone->free_area[order];
+
+	list_add(&page->lru, &area->free_list[migratetype]);
+	area->nr_free++;
+}
+
+/* Used for pages not on another list */
+static inline void add_to_free_list_tail(struct page *page, struct zone *zone,
+					 unsigned int order, int migratetype)
+{
+	struct free_area *area = &zone->free_area[order];
+
+	list_add_tail(&page->lru, &area->free_list[migratetype]);
+	area->nr_free++;
+}
+
+/* Used for pages which are on another list */
+static inline void move_to_free_list(struct page *page, struct zone *zone,
+				     unsigned int order, int migratetype)
+{
+	struct free_area *area = &zone->free_area[order];
+
+	list_move(&page->lru, &area->free_list[migratetype]);
+}
+
+static inline void del_page_from_free_list(struct page *page, struct zone *zone,
+					   unsigned int order)
+{
+	list_del(&page->lru);
+	__ClearPageBuddy(page);
+	set_page_private(page, 0);
+	zone->free_area[order].nr_free--;
+}
+
 /*
  * If this is not the largest possible page, check if the buddy
  * of the next-highest order is free. If it is, it's possible
@@ -932,7 +970,6 @@ static inline void __free_one_page(struct page *page,
 	struct capture_control *capc = task_capc(zone);
 	unsigned long uninitialized_var(buddy_pfn);
 	unsigned long combined_pfn;
-	struct free_area *area;
 	unsigned int max_order;
 	struct page *buddy;
 	bool to_tail;
@@ -970,7 +1007,7 @@ static inline void __free_one_page(struct page *page,
 		if (page_is_guard(buddy))
 			clear_page_guard(zone, buddy, order, migratetype);
 		else
-			del_page_from_free_area(buddy, &zone->free_area[order]);
+			del_page_from_free_list(buddy, zone, order);
 		combined_pfn = buddy_pfn & pfn;
 		page = page + (combined_pfn - pfn);
 		pfn = combined_pfn;
@@ -1004,16 +1041,15 @@ static inline void __free_one_page(struct page *page,
 done_merging:
 	set_page_order(page, order);
 
-	area = &zone->free_area[order];
 	if (is_shuffle_order(order))
 		to_tail = shuffle_pick_tail();
 	else
 		to_tail = buddy_merge_likely(pfn, buddy_pfn, page, order);
 
 	if (to_tail)
-		add_to_free_area_tail(page, area, migratetype);
+		add_to_free_list_tail(page, zone, order, migratetype);
 	else
-		add_to_free_area(page, area, migratetype);
+		add_to_free_list(page, zone, order, migratetype);
 }
 
 /*
@@ -2027,13 +2063,11 @@ void __init init_cma_reserved_pageblock(struct page *page)
  * -- nyc
  */
 static inline void expand(struct zone *zone, struct page *page,
-	int low, int high, struct free_area *area,
-	int migratetype)
+	int low, int high, int migratetype)
 {
 	unsigned long size = 1 << high;
 
 	while (high > low) {
-		area--;
 		high--;
 		size >>= 1;
 		VM_BUG_ON_PAGE(bad_range(zone, &page[size]), &page[size]);
@@ -2047,7 +2081,7 @@ static inline void expand(struct zone *zone, struct page *page,
 		if (set_page_guard(zone, &page[size], high, migratetype))
 			continue;
 
-		add_to_free_area(&page[size], area, migratetype);
+		add_to_free_list(&page[size], zone, high, migratetype);
 		set_page_order(&page[size], high);
 	}
 }
@@ -2205,8 +2239,8 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
 		page = get_page_from_free_area(area, migratetype);
 		if (!page)
 			continue;
-		del_page_from_free_area(page, area);
-		expand(zone, page, order, current_order, area, migratetype);
+		del_page_from_free_list(page, zone, current_order);
+		expand(zone, page, order, current_order, migratetype);
 		set_pcppage_migratetype(page, migratetype);
 		return page;
 	}
@@ -2280,7 +2314,7 @@ static int move_freepages(struct zone *zone,
 		VM_BUG_ON_PAGE(page_zone(page) != zone, page);
 
 		order = page_order(page);
-		move_to_free_area(page, &zone->free_area[order], migratetype);
+		move_to_free_list(page, zone, order, migratetype);
 		page += 1 << order;
 		pages_moved += 1 << order;
 	}
@@ -2396,7 +2430,6 @@ static void steal_suitable_fallback(struct zone *zone, struct page *page,
 		unsigned int alloc_flags, int start_type, bool whole_block)
 {
 	unsigned int current_order = page_order(page);
-	struct free_area *area;
 	int free_pages, movable_pages, alike_pages;
 	int old_block_type;
 
@@ -2467,8 +2500,7 @@ static void steal_suitable_fallback(struct zone *zone, struct page *page,
 	return;
 
 single_page:
-	area = &zone->free_area[current_order];
-	move_to_free_area(page, area, start_type);
+	move_to_free_list(page, zone, current_order, start_type);
 }
 
 /*
@@ -3139,7 +3171,6 @@ void split_page(struct page *page, unsigned int order)
 
 int __isolate_free_page(struct page *page, unsigned int order)
 {
-	struct free_area *area = &page_zone(page)->free_area[order];
 	unsigned long watermark;
 	struct zone *zone;
 	int mt;
@@ -3165,7 +3196,7 @@ int __isolate_free_page(struct page *page, unsigned int order)
 
 	/* Remove page from free list */
 
-	del_page_from_free_area(page, area);
+	del_page_from_free_list(page, zone, order);
 
 	/*
 	 * Set the pageblock if the isolated page is at least half of a
@@ -8722,7 +8753,7 @@ void zone_pcp_reset(struct zone *zone)
 		BUG_ON(!PageBuddy(page));
 		order = page_order(page);
 		offlined_pages += 1 << order;
-		del_page_from_free_area(page, &zone->free_area[order]);
+		del_page_from_free_list(page, zone, order);
 		pfn += (1 << order);
 	}
 	spin_unlock_irqrestore(&zone->lock, flags);


^ permalink raw reply	[flat|nested] 29+ messages in thread

* [PATCH v17 3/9] mm: Add function __putback_isolated_page
  2020-02-11 22:45 [PATCH v17 0/9] mm / virtio: Provide support for free page reporting Alexander Duyck
  2020-02-11 22:46 ` [PATCH v17 1/9] mm: Adjust shuffle code to allow for future coalescing Alexander Duyck
  2020-02-11 22:46 ` [PATCH v17 2/9] mm: Use zone and order instead of free area in free_list manipulators Alexander Duyck
@ 2020-02-11 22:46 ` Alexander Duyck
  2020-02-19 14:33   ` Mel Gorman
  2020-02-11 22:46 ` [PATCH v17 4/9] mm: Introduce Reported pages Alexander Duyck
                   ` (10 subsequent siblings)
  13 siblings, 1 reply; 29+ messages in thread
From: Alexander Duyck @ 2020-02-11 22:46 UTC (permalink / raw)
  To: kvm, david, mst, linux-kernel, linux-mm, akpm, mgorman
  Cc: yang.zhang.wz, pagupta, konrad.wilk, nitesh, riel, willy,
	lcapitulino, dave.hansen, wei.w.wang, aarcange, pbonzini,
	dan.j.williams, mhocko, alexander.h.duyck, vbabka, osalvador

From: Alexander Duyck <alexander.h.duyck@linux.intel.com>

There are cases where we would benefit from avoiding having to go through
the allocation and free cycle to return an isolated page.

Examples for this might include page poisoning in which we isolate a page
and then put it back in the free list without ever having actually
allocated it.

This will enable us to also avoid notifiers for the future free page
reporting which will need to avoid retriggering page reporting when
returning pages that have been reported on.

Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
---
 mm/internal.h       |    2 ++
 mm/page_alloc.c     |   19 +++++++++++++++++++
 mm/page_isolation.c |    6 ++----
 3 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index 3cf20ab3ca01..7b108222e5f4 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -157,6 +157,8 @@ static inline struct page *pageblock_pfn_to_page(unsigned long start_pfn,
 }
 
 extern int __isolate_free_page(struct page *page, unsigned int order);
+extern void __putback_isolated_page(struct page *page, unsigned int order,
+				    int mt);
 extern void memblock_free_pages(struct page *page, unsigned long pfn,
 					unsigned int order);
 extern void __free_pages_core(struct page *page, unsigned int order);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index de916aa06a27..b711fc0159d9 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3217,6 +3217,25 @@ int __isolate_free_page(struct page *page, unsigned int order)
 	return 1UL << order;
 }
 
+/**
+ * __putback_isolated_page - Return a now-isolated page back where we got it
+ * @page: Page that was isolated
+ * @order: Order of the isolated page
+ *
+ * This function is meant to return a page pulled from the free lists via
+ * __isolate_free_page back to the free lists they were pulled from.
+ */
+void __putback_isolated_page(struct page *page, unsigned int order, int mt)
+{
+	struct zone *zone = page_zone(page);
+
+	/* zone lock should be held when this function is called */
+	lockdep_assert_held(&zone->lock);
+
+	/* Return isolated page to tail of freelist. */
+	__free_one_page(page, page_to_pfn(page), zone, order, mt);
+}
+
 /*
  * Update NUMA hit/miss statistics
  *
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index a9fd7c740c23..2c11a38d6e87 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -117,13 +117,11 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
 		__mod_zone_freepage_state(zone, nr_pages, migratetype);
 	}
 	set_pageblock_migratetype(page, migratetype);
+	if (isolated_page)
+		__putback_isolated_page(page, order, migratetype);
 	zone->nr_isolate_pageblock--;
 out:
 	spin_unlock_irqrestore(&zone->lock, flags);
-	if (isolated_page) {
-		post_alloc_hook(page, order, __GFP_MOVABLE);
-		__free_pages(page, order);
-	}
 }
 
 static inline struct page *


^ permalink raw reply	[flat|nested] 29+ messages in thread

* [PATCH v17 4/9] mm: Introduce Reported pages
  2020-02-11 22:45 [PATCH v17 0/9] mm / virtio: Provide support for free page reporting Alexander Duyck
                   ` (2 preceding siblings ...)
  2020-02-11 22:46 ` [PATCH v17 3/9] mm: Add function __putback_isolated_page Alexander Duyck
@ 2020-02-11 22:46 ` Alexander Duyck
  2020-02-19 14:55   ` Mel Gorman
  2020-02-11 22:46 ` [PATCH v17 5/9] virtio-balloon: Pull page poisoning config out of free page hinting Alexander Duyck
                   ` (9 subsequent siblings)
  13 siblings, 1 reply; 29+ messages in thread
From: Alexander Duyck @ 2020-02-11 22:46 UTC (permalink / raw)
  To: kvm, david, mst, linux-kernel, linux-mm, akpm, mgorman
  Cc: yang.zhang.wz, pagupta, konrad.wilk, nitesh, riel, willy,
	lcapitulino, dave.hansen, wei.w.wang, aarcange, pbonzini,
	dan.j.williams, mhocko, alexander.h.duyck, vbabka, osalvador

From: Alexander Duyck <alexander.h.duyck@linux.intel.com>

In order to pave the way for free page reporting in virtualized
environments we will need a way to get pages out of the free lists and
identify those pages after they have been returned. To accomplish this,
this patch adds the concept of a Reported Buddy, which is essentially
meant to just be the Uptodate flag used in conjunction with the Buddy
page type.

To prevent the reported pages from leaking outside of the buddy lists I
added a check to clear the PageReported bit in the del_page_from_free_list
function. As a result any reported page that is split, merged, or
allocated will have the flag cleared prior to the PageBuddy value being
cleared.

The process for reporting pages is fairly simple. Once we free a page that
meets the minimum order for page reporting we will schedule a worker thread
to start 2s or more in the future. That worker thread will begin working
from the lowest supported page reporting order up to MAX_ORDER - 1 pulling
unreported pages from the free list and storing them in the scatterlist.

When processing each individual free list it is necessary for the worker
thread to release the zone lock when it needs to stop and report the full
scatterlist of pages. To reduce the work of the next iteration the worker
thread will rotate the free list so that the first unreported page in the
free list becomes the first entry in the list.

It will then call a reporting function providing information on how many
entries are in the scatterlist. Once the function completes it will return
the pages to the free area from which they were allocated and start over
pulling more pages from the free areas until there are no longer enough
pages to report on to keep the worker busy, or we have processed as many
pages as were contained in the free area when we started processing the
list.

The worker thread will work in a round-robin fashion making its way
though each zone requesting reporting, and through each reportable free
list within that zone. Once all free areas within the zone have been
processed it will check to see if there have been any requests for
reporting while it was processing. If so it will reschedule the worker
thread to start up again in roughly 2s and exit.

Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
---
 include/linux/page-flags.h     |   11 +
 include/linux/page_reporting.h |   25 +++
 mm/Kconfig                     |   11 +
 mm/Makefile                    |    1 
 mm/page_alloc.c                |   17 ++
 mm/page_reporting.c            |  319 ++++++++++++++++++++++++++++++++++++++++
 mm/page_reporting.h            |   54 +++++++
 7 files changed, 434 insertions(+), 4 deletions(-)
 create mode 100644 include/linux/page_reporting.h
 create mode 100644 mm/page_reporting.c
 create mode 100644 mm/page_reporting.h

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 1bf83c8fcaa7..49c2697046b9 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -163,6 +163,9 @@ enum pageflags {
 
 	/* non-lru isolated movable page */
 	PG_isolated = PG_reclaim,
+
+	/* Only valid for buddy pages. Used to track pages that are reported */
+	PG_reported = PG_uptodate,
 };
 
 #ifndef __GENERATING_BOUNDS_H
@@ -432,6 +435,14 @@ static inline bool set_hwpoison_free_buddy_page(struct page *page)
 #endif
 
 /*
+ * PageReported() is used to track reported free pages within the Buddy
+ * allocator. We can use the non-atomic version of the test and set
+ * operations as both should be shielded with the zone lock to prevent
+ * any possible races on the setting or clearing of the bit.
+ */
+__PAGEFLAG(Reported, reported, PF_NO_COMPOUND)
+
+/*
  * On an anonymous page mapped into a user virtual memory area,
  * page->mapping points to its anon_vma, not to a struct address_space;
  * with the PAGE_MAPPING_ANON bit set to distinguish it.  See rmap.h.
diff --git a/include/linux/page_reporting.h b/include/linux/page_reporting.h
new file mode 100644
index 000000000000..32355486f572
--- /dev/null
+++ b/include/linux/page_reporting.h
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_PAGE_REPORTING_H
+#define _LINUX_PAGE_REPORTING_H
+
+#include <linux/mmzone.h>
+#include <linux/scatterlist.h>
+
+#define PAGE_REPORTING_CAPACITY		32
+
+struct page_reporting_dev_info {
+	/* function that alters pages to make them "reported" */
+	int (*report)(struct page_reporting_dev_info *prdev,
+		      struct scatterlist *sg, unsigned int nents);
+
+	/* work struct for processing reports */
+	struct delayed_work work;
+
+	/* Current state of page reporting */
+	atomic_t state;
+};
+
+/* Tear-down and bring-up for page reporting devices */
+void page_reporting_unregister(struct page_reporting_dev_info *prdev);
+int page_reporting_register(struct page_reporting_dev_info *prdev);
+#endif /*_LINUX_PAGE_REPORTING_H */
diff --git a/mm/Kconfig b/mm/Kconfig
index ab80933be65f..d40a873402ff 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -237,6 +237,17 @@ config COMPACTION
 	  linux-mm@kvack.org.
 
 #
+# support for free page reporting
+config PAGE_REPORTING
+	bool "Free page reporting"
+	def_bool n
+	help
+	  Free page reporting allows for the incremental acquisition of
+	  free pages from the buddy allocator for the purpose of reporting
+	  those pages to another entity, such as a hypervisor, so that the
+	  memory can be freed within the host for other uses.
+
+#
 # support for page migration
 #
 config MIGRATION
diff --git a/mm/Makefile b/mm/Makefile
index c9696f3ec840..7b5eec34d0e9 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -118,3 +118,4 @@ obj-$(CONFIG_HMM_MIRROR) += hmm.o
 obj-$(CONFIG_MEMFD_CREATE) += memfd.o
 obj-$(CONFIG_MAPPING_DIRTY_HELPERS) += mapping_dirty_helpers.o
 obj-$(CONFIG_PTDUMP_CORE) += ptdump.o
+obj-$(CONFIG_PAGE_REPORTING) += page_reporting.o
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b711fc0159d9..1142b2f91377 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -74,6 +74,7 @@
 #include <asm/div64.h>
 #include "internal.h"
 #include "shuffle.h"
+#include "page_reporting.h"
 
 /* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
 static DEFINE_MUTEX(pcp_batch_high_lock);
@@ -902,6 +903,10 @@ static inline void move_to_free_list(struct page *page, struct zone *zone,
 static inline void del_page_from_free_list(struct page *page, struct zone *zone,
 					   unsigned int order)
 {
+	/* clear reported state and update reported page count */
+	if (page_reported(page))
+		__ClearPageReported(page);
+
 	list_del(&page->lru);
 	__ClearPageBuddy(page);
 	set_page_private(page, 0);
@@ -965,7 +970,7 @@ static inline void del_page_from_free_list(struct page *page, struct zone *zone,
 static inline void __free_one_page(struct page *page,
 		unsigned long pfn,
 		struct zone *zone, unsigned int order,
-		int migratetype)
+		int migratetype, bool report)
 {
 	struct capture_control *capc = task_capc(zone);
 	unsigned long uninitialized_var(buddy_pfn);
@@ -1050,6 +1055,10 @@ static inline void __free_one_page(struct page *page,
 		add_to_free_list_tail(page, zone, order, migratetype);
 	else
 		add_to_free_list(page, zone, order, migratetype);
+
+	/* Notify page reporting subsystem of freed page */
+	if (report)
+		page_reporting_notify_free(order);
 }
 
 /*
@@ -1366,7 +1375,7 @@ static void free_pcppages_bulk(struct zone *zone, int count,
 		if (unlikely(isolated_pageblocks))
 			mt = get_pageblock_migratetype(page);
 
-		__free_one_page(page, page_to_pfn(page), zone, 0, mt);
+		__free_one_page(page, page_to_pfn(page), zone, 0, mt, true);
 		trace_mm_page_pcpu_drain(page, 0, mt);
 	}
 	spin_unlock(&zone->lock);
@@ -1382,7 +1391,7 @@ static void free_one_page(struct zone *zone,
 		is_migrate_isolate(migratetype))) {
 		migratetype = get_pfnblock_migratetype(page, pfn);
 	}
-	__free_one_page(page, pfn, zone, order, migratetype);
+	__free_one_page(page, pfn, zone, order, migratetype, true);
 	spin_unlock(&zone->lock);
 }
 
@@ -3233,7 +3242,7 @@ void __putback_isolated_page(struct page *page, unsigned int order, int mt)
 	lockdep_assert_held(&zone->lock);
 
 	/* Return isolated page to tail of freelist. */
-	__free_one_page(page, page_to_pfn(page), zone, order, mt);
+	__free_one_page(page, page_to_pfn(page), zone, order, mt, false);
 }
 
 /*
diff --git a/mm/page_reporting.c b/mm/page_reporting.c
new file mode 100644
index 000000000000..1047c6872d4f
--- /dev/null
+++ b/mm/page_reporting.c
@@ -0,0 +1,319 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/mm.h>
+#include <linux/mmzone.h>
+#include <linux/page_reporting.h>
+#include <linux/gfp.h>
+#include <linux/export.h>
+#include <linux/delay.h>
+#include <linux/scatterlist.h>
+
+#include "page_reporting.h"
+#include "internal.h"
+
+#define PAGE_REPORTING_DELAY	(2 * HZ)
+static struct page_reporting_dev_info __rcu *pr_dev_info __read_mostly;
+
+enum {
+	PAGE_REPORTING_IDLE = 0,
+	PAGE_REPORTING_REQUESTED,
+	PAGE_REPORTING_ACTIVE
+};
+
+/* request page reporting */
+static void
+__page_reporting_request(struct page_reporting_dev_info *prdev)
+{
+	unsigned int state;
+
+	/* Check to see if we are in desired state */
+	state = atomic_read(&prdev->state);
+	if (state == PAGE_REPORTING_REQUESTED)
+		return;
+
+	/*
+	 *  If reporting is already active there is nothing we need to do.
+	 *  Test against 0 as that represents PAGE_REPORTING_IDLE.
+	 */
+	state = atomic_xchg(&prdev->state, PAGE_REPORTING_REQUESTED);
+	if (state != PAGE_REPORTING_IDLE)
+		return;
+
+	/*
+	 * Delay the start of work to allow a sizable queue to build. For
+	 * now we are limiting this to running no more than once every
+	 * couple of seconds.
+	 */
+	schedule_delayed_work(&prdev->work, PAGE_REPORTING_DELAY);
+}
+
+/* notify prdev of free page reporting request */
+void __page_reporting_notify(void)
+{
+	struct page_reporting_dev_info *prdev;
+
+	/*
+	 * We use RCU to protect the pr_dev_info pointer. In almost all
+	 * cases this should be present, however in the unlikely case of
+	 * a shutdown this will be NULL and we should exit.
+	 */
+	rcu_read_lock();
+	prdev = rcu_dereference(pr_dev_info);
+	if (likely(prdev))
+		__page_reporting_request(prdev);
+
+	rcu_read_unlock();
+}
+
+static void
+page_reporting_drain(struct page_reporting_dev_info *prdev,
+		     struct scatterlist *sgl, unsigned int nents, bool reported)
+{
+	struct scatterlist *sg = sgl;
+
+	/*
+	 * Drain the now reported pages back into their respective
+	 * free lists/areas. We assume at least one page is populated.
+	 */
+	do {
+		struct page *page = sg_page(sg);
+		int mt = get_pageblock_migratetype(page);
+		unsigned int order = get_order(sg->length);
+
+		__putback_isolated_page(page, order, mt);
+
+		/* If the pages were not reported due to error skip flagging */
+		if (!reported)
+			continue;
+
+		/*
+		 * If page was not comingled with another page we can
+		 * consider the result to be "reported" since the page
+		 * hasn't been modified, otherwise we will need to
+		 * report on the new larger page when we make our way
+		 * up to that higher order.
+		 */
+		if (PageBuddy(page) && page_order(page) == order)
+			__SetPageReported(page);
+	} while ((sg = sg_next(sg)));
+
+	/* reinitialize scatterlist now that it is empty */
+	sg_init_table(sgl, nents);
+}
+
+/*
+ * The page reporting cycle consists of 4 stages, fill, report, drain, and
+ * idle. We will cycle through the first 3 stages until we cannot obtain a
+ * full scatterlist of pages, in that case we will switch to idle.
+ */
+static int
+page_reporting_cycle(struct page_reporting_dev_info *prdev, struct zone *zone,
+		     unsigned int order, unsigned int mt,
+		     struct scatterlist *sgl, unsigned int *offset)
+{
+	struct free_area *area = &zone->free_area[order];
+	struct list_head *list = &area->free_list[mt];
+	unsigned int page_len = PAGE_SIZE << order;
+	struct page *page, *next;
+	int err = 0;
+
+	/*
+	 * Perform early check, if free area is empty there is
+	 * nothing to process so we can skip this free_list.
+	 */
+	if (list_empty(list))
+		return err;
+
+	spin_lock_irq(&zone->lock);
+
+	/* loop through free list adding unreported pages to sg list */
+	list_for_each_entry_safe(page, next, list, lru) {
+		/* We are going to skip over the reported pages. */
+		if (PageReported(page))
+			continue;
+
+		/* Attempt to pull page from list */
+		if (!__isolate_free_page(page, order))
+			break;
+
+		/* Add page to scatter list */
+		--(*offset);
+		sg_set_page(&sgl[*offset], page, page_len, 0);
+
+		/* If scatterlist isn't full grab more pages */
+		if (*offset)
+			continue;
+
+		/* release lock before waiting on report processing */
+		spin_unlock_irq(&zone->lock);
+
+		/* begin processing pages in local list */
+		err = prdev->report(prdev, sgl, PAGE_REPORTING_CAPACITY);
+
+		/* reset offset since the full list was reported */
+		*offset = PAGE_REPORTING_CAPACITY;
+
+		/* reacquire zone lock and resume processing */
+		spin_lock_irq(&zone->lock);
+
+		/* flush reported pages from the sg list */
+		page_reporting_drain(prdev, sgl, PAGE_REPORTING_CAPACITY, !err);
+
+		/*
+		 * Reset next to first entry, the old next isn't valid
+		 * since we dropped the lock to report the pages
+		 */
+		next = list_first_entry(list, struct page, lru);
+
+		/* exit on error */
+		if (err)
+			break;
+	}
+
+	spin_unlock_irq(&zone->lock);
+
+	return err;
+}
+
+static int
+page_reporting_process_zone(struct page_reporting_dev_info *prdev,
+			    struct scatterlist *sgl, struct zone *zone)
+{
+	unsigned int order, mt, leftover, offset = PAGE_REPORTING_CAPACITY;
+	unsigned long watermark;
+	int err = 0;
+
+	/* Generate minimum watermark to be able to guarantee progress */
+	watermark = low_wmark_pages(zone) +
+		    (PAGE_REPORTING_CAPACITY << PAGE_REPORTING_MIN_ORDER);
+
+	/*
+	 * Cancel request if insufficient free memory or if we failed
+	 * to allocate page reporting statistics for the zone.
+	 */
+	if (!zone_watermark_ok(zone, 0, watermark, 0, ALLOC_CMA))
+		return err;
+
+	/* Process each free list starting from lowest order/mt */
+	for (order = PAGE_REPORTING_MIN_ORDER; order < MAX_ORDER; order++) {
+		for (mt = 0; mt < MIGRATE_TYPES; mt++) {
+			/* We do not pull pages from the isolate free list */
+			if (is_migrate_isolate(mt))
+				continue;
+
+			err = page_reporting_cycle(prdev, zone, order, mt,
+						   sgl, &offset);
+			if (err)
+				return err;
+		}
+	}
+
+	/* report the leftover pages before going idle */
+	leftover = PAGE_REPORTING_CAPACITY - offset;
+	if (leftover) {
+		sgl = &sgl[offset];
+		err = prdev->report(prdev, sgl, leftover);
+
+		/* flush any remaining pages out from the last report */
+		spin_lock_irq(&zone->lock);
+		page_reporting_drain(prdev, sgl, leftover, !err);
+		spin_unlock_irq(&zone->lock);
+	}
+
+	return err;
+}
+
+static void page_reporting_process(struct work_struct *work)
+{
+	struct delayed_work *d_work = to_delayed_work(work);
+	struct page_reporting_dev_info *prdev =
+		container_of(d_work, struct page_reporting_dev_info, work);
+	int err = 0, state = PAGE_REPORTING_ACTIVE;
+	struct scatterlist *sgl;
+	struct zone *zone;
+
+	/*
+	 * Change the state to "Active" so that we can track if there is
+	 * anyone requests page reporting after we complete our pass. If
+	 * the state is not altered by the end of the pass we will switch
+	 * to idle and quit scheduling reporting runs.
+	 */
+	atomic_set(&prdev->state, state);
+
+	/* allocate scatterlist to store pages being reported on */
+	sgl = kmalloc_array(PAGE_REPORTING_CAPACITY, sizeof(*sgl), GFP_KERNEL);
+	if (!sgl)
+		goto err_out;
+
+	sg_init_table(sgl, PAGE_REPORTING_CAPACITY);
+
+	for_each_zone(zone) {
+		err = page_reporting_process_zone(prdev, sgl, zone);
+		if (err)
+			break;
+	}
+
+	kfree(sgl);
+err_out:
+	/*
+	 * If the state has reverted back to requested then there may be
+	 * additional pages to be processed. We will defer for 2s to allow
+	 * more pages to accumulate.
+	 */
+	state = atomic_cmpxchg(&prdev->state, state, PAGE_REPORTING_IDLE);
+	if (state == PAGE_REPORTING_REQUESTED)
+		schedule_delayed_work(&prdev->work, PAGE_REPORTING_DELAY);
+}
+
+static DEFINE_MUTEX(page_reporting_mutex);
+DEFINE_STATIC_KEY_FALSE(page_reporting_enabled);
+
+int page_reporting_register(struct page_reporting_dev_info *prdev)
+{
+	int err = 0;
+
+	mutex_lock(&page_reporting_mutex);
+
+	/* nothing to do if already in use */
+	if (rcu_access_pointer(pr_dev_info)) {
+		err = -EBUSY;
+		goto err_out;
+	}
+
+	/* initialize state and work structures */
+	atomic_set(&prdev->state, PAGE_REPORTING_IDLE);
+	INIT_DELAYED_WORK(&prdev->work, &page_reporting_process);
+
+	/* Begin initial flush of zones */
+	__page_reporting_request(prdev);
+
+	/* Assign device to allow notifications */
+	rcu_assign_pointer(pr_dev_info, prdev);
+
+	/* enable page reporting notification */
+	if (!static_key_enabled(&page_reporting_enabled)) {
+		static_branch_enable(&page_reporting_enabled);
+		pr_info("Free page reporting enabled\n");
+	}
+err_out:
+	mutex_unlock(&page_reporting_mutex);
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(page_reporting_register);
+
+void page_reporting_unregister(struct page_reporting_dev_info *prdev)
+{
+	mutex_lock(&page_reporting_mutex);
+
+	if (rcu_access_pointer(pr_dev_info) == prdev) {
+		/* Disable page reporting notification */
+		RCU_INIT_POINTER(pr_dev_info, NULL);
+		synchronize_rcu();
+
+		/* Flush any existing work, and lock it out */
+		cancel_delayed_work_sync(&prdev->work);
+	}
+
+	mutex_unlock(&page_reporting_mutex);
+}
+EXPORT_SYMBOL_GPL(page_reporting_unregister);
diff --git a/mm/page_reporting.h b/mm/page_reporting.h
new file mode 100644
index 000000000000..aa6d37f4dc22
--- /dev/null
+++ b/mm/page_reporting.h
@@ -0,0 +1,54 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _MM_PAGE_REPORTING_H
+#define _MM_PAGE_REPORTING_H
+
+#include <linux/mmzone.h>
+#include <linux/pageblock-flags.h>
+#include <linux/page-isolation.h>
+#include <linux/jump_label.h>
+#include <linux/slab.h>
+#include <asm/pgtable.h>
+#include <linux/scatterlist.h>
+
+#define PAGE_REPORTING_MIN_ORDER	pageblock_order
+
+#ifdef CONFIG_PAGE_REPORTING
+DECLARE_STATIC_KEY_FALSE(page_reporting_enabled);
+void __page_reporting_notify(void);
+
+static inline bool page_reported(struct page *page)
+{
+	return static_branch_unlikely(&page_reporting_enabled) &&
+	       PageReported(page);
+}
+
+/**
+ * page_reporting_notify_free - Free page notification to start page processing
+ *
+ * This function is meant to act as a screener for __page_reporting_notify
+ * which will determine if a give zone has crossed over the high-water mark
+ * that will justify us beginning page treatment. If we have crossed that
+ * threshold then it will start the process of pulling some pages and
+ * placing them in the batch list for treatment.
+ */
+static inline void page_reporting_notify_free(unsigned int order)
+{
+	/* Called from hot path in __free_one_page() */
+	if (!static_branch_unlikely(&page_reporting_enabled))
+		return;
+
+	/* Determine if we have crossed reporting threshold */
+	if (order < PAGE_REPORTING_MIN_ORDER)
+		return;
+
+	/* This will add a few cycles, but should be called infrequently */
+	__page_reporting_notify();
+}
+#else /* CONFIG_PAGE_REPORTING */
+#define page_reported(_page)	false
+
+static inline void page_reporting_notify_free(unsigned int order)
+{
+}
+#endif /* CONFIG_PAGE_REPORTING */
+#endif /*_MM_PAGE_REPORTING_H */


^ permalink raw reply	[flat|nested] 29+ messages in thread

* [PATCH v17 5/9] virtio-balloon: Pull page poisoning config out of free page hinting
  2020-02-11 22:45 [PATCH v17 0/9] mm / virtio: Provide support for free page reporting Alexander Duyck
                   ` (3 preceding siblings ...)
  2020-02-11 22:46 ` [PATCH v17 4/9] mm: Introduce Reported pages Alexander Duyck
@ 2020-02-11 22:46 ` Alexander Duyck
  2020-02-11 22:46 ` [PATCH v17 6/9] virtio-balloon: Add support for providing free page reports to host Alexander Duyck
                   ` (8 subsequent siblings)
  13 siblings, 0 replies; 29+ messages in thread
From: Alexander Duyck @ 2020-02-11 22:46 UTC (permalink / raw)
  To: kvm, david, mst, linux-kernel, linux-mm, akpm, mgorman
  Cc: yang.zhang.wz, pagupta, konrad.wilk, nitesh, riel, willy,
	lcapitulino, dave.hansen, wei.w.wang, aarcange, pbonzini,
	dan.j.williams, mhocko, alexander.h.duyck, vbabka, osalvador

From: Alexander Duyck <alexander.h.duyck@linux.intel.com>

Currently the page poisoning setting wasn't being enabled unless free page
hinting was enabled. However we will need the page poisoning tracking logic
as well for free page reporting. As such pull it out and make it a separate
bit of config in the probe function.

In addition we need to add support for the more recent init_on_free feature
which expects a behavior similar to page poisoning in that we expect the
page to be pre-zeroed.

Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
---
 drivers/virtio/virtio_balloon.c |   23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 7bfe365d9372..98d09825f2e2 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -864,7 +864,6 @@ static int virtio_balloon_register_shrinker(struct virtio_balloon *vb)
 static int virtballoon_probe(struct virtio_device *vdev)
 {
 	struct virtio_balloon *vb;
-	__u32 poison_val;
 	int err;
 
 	if (!vdev->config->get) {
@@ -930,11 +929,20 @@ static int virtballoon_probe(struct virtio_device *vdev)
 						  VIRTIO_BALLOON_CMD_ID_STOP);
 		spin_lock_init(&vb->free_page_list_lock);
 		INIT_LIST_HEAD(&vb->free_page_list);
-		if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) {
+	}
+	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) {
+		/* Start with poison val of 0 representing general init */
+		__u32 poison_val = 0;
+
+		/*
+		 * Let the hypervisor know that we are expecting a
+		 * specific value to be written back in balloon pages.
+		 */
+		if (!want_init_on_free())
 			memset(&poison_val, PAGE_POISON, sizeof(poison_val));
-			virtio_cwrite(vb->vdev, struct virtio_balloon_config,
-				      poison_val, &poison_val);
-		}
+
+		virtio_cwrite(vb->vdev, struct virtio_balloon_config,
+			      poison_val, &poison_val);
 	}
 	/*
 	 * We continue to use VIRTIO_BALLOON_F_DEFLATE_ON_OOM to decide if a
@@ -1045,7 +1053,10 @@ static int virtballoon_restore(struct virtio_device *vdev)
 
 static int virtballoon_validate(struct virtio_device *vdev)
 {
-	if (!page_poisoning_enabled())
+	/* Tell the host whether we care about poisoned pages. */
+	if (!want_init_on_free() &&
+	    (IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY) ||
+	     !page_poisoning_enabled()))
 		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_POISON);
 
 	__virtio_clear_bit(vdev, VIRTIO_F_IOMMU_PLATFORM);


^ permalink raw reply	[flat|nested] 29+ messages in thread

* [PATCH v17 6/9] virtio-balloon: Add support for providing free page reports to host
  2020-02-11 22:45 [PATCH v17 0/9] mm / virtio: Provide support for free page reporting Alexander Duyck
                   ` (4 preceding siblings ...)
  2020-02-11 22:46 ` [PATCH v17 5/9] virtio-balloon: Pull page poisoning config out of free page hinting Alexander Duyck
@ 2020-02-11 22:46 ` Alexander Duyck
  2020-02-11 22:47 ` [PATCH v17 7/9] mm/page_reporting: Rotate reported pages to the tail of the list Alexander Duyck
                   ` (7 subsequent siblings)
  13 siblings, 0 replies; 29+ messages in thread
From: Alexander Duyck @ 2020-02-11 22:46 UTC (permalink / raw)
  To: kvm, david, mst, linux-kernel, linux-mm, akpm, mgorman
  Cc: yang.zhang.wz, pagupta, konrad.wilk, nitesh, riel, willy,
	lcapitulino, dave.hansen, wei.w.wang, aarcange, pbonzini,
	dan.j.williams, mhocko, alexander.h.duyck, vbabka, osalvador

From: Alexander Duyck <alexander.h.duyck@linux.intel.com>

Add support for the page reporting feature provided by virtio-balloon.
Reporting differs from the regular balloon functionality in that is is
much less durable than a standard memory balloon. Instead of creating a
list of pages that cannot be accessed the pages are only inaccessible
while they are being indicated to the virtio interface. Once the
interface has acknowledged them they are placed back into their respective
free lists and are once again accessible by the guest system.

Unlike a standard balloon we don't inflate and deflate the pages. Instead
we perform the reporting, and once the reporting is completed it is
assumed that the page has been dropped from the guest and will be faulted
back in the next time the page is accessed.

Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
---
 drivers/virtio/Kconfig              |    1 +
 drivers/virtio/virtio_balloon.c     |   64 +++++++++++++++++++++++++++++++++++
 include/uapi/linux/virtio_balloon.h |    1 +
 3 files changed, 66 insertions(+)

diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
index 078615cf2afc..4b2dd8259ff5 100644
--- a/drivers/virtio/Kconfig
+++ b/drivers/virtio/Kconfig
@@ -58,6 +58,7 @@ config VIRTIO_BALLOON
 	tristate "Virtio balloon driver"
 	depends on VIRTIO
 	select MEMORY_BALLOON
+	select PAGE_REPORTING
 	---help---
 	 This driver supports increasing and decreasing the amount
 	 of memory within a KVM guest.
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 98d09825f2e2..8511d258dbb4 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -19,6 +19,7 @@
 #include <linux/mount.h>
 #include <linux/magic.h>
 #include <linux/pseudo_fs.h>
+#include <linux/page_reporting.h>
 
 /*
  * Balloon device works in 4K page units.  So each page is pointed to by
@@ -47,6 +48,7 @@ enum virtio_balloon_vq {
 	VIRTIO_BALLOON_VQ_DEFLATE,
 	VIRTIO_BALLOON_VQ_STATS,
 	VIRTIO_BALLOON_VQ_FREE_PAGE,
+	VIRTIO_BALLOON_VQ_REPORTING,
 	VIRTIO_BALLOON_VQ_MAX
 };
 
@@ -114,6 +116,10 @@ struct virtio_balloon {
 
 	/* To register a shrinker to shrink memory upon memory pressure */
 	struct shrinker shrinker;
+
+	/* Free page reporting device */
+	struct virtqueue *reporting_vq;
+	struct page_reporting_dev_info pr_dev_info;
 };
 
 static struct virtio_device_id id_table[] = {
@@ -153,6 +159,33 @@ static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
 
 }
 
+int virtballoon_free_page_report(struct page_reporting_dev_info *pr_dev_info,
+				   struct scatterlist *sg, unsigned int nents)
+{
+	struct virtio_balloon *vb =
+		container_of(pr_dev_info, struct virtio_balloon, pr_dev_info);
+	struct virtqueue *vq = vb->reporting_vq;
+	unsigned int unused, err;
+
+	/* We should always be able to add these buffers to an empty queue. */
+	err = virtqueue_add_inbuf(vq, sg, nents, vb, GFP_NOWAIT | __GFP_NOWARN);
+
+	/*
+	 * In the extremely unlikely case that something has occurred and we
+	 * are able to trigger an error we will simply display a warning
+	 * and exit without actually processing the pages.
+	 */
+	if (WARN_ON_ONCE(err))
+		return err;
+
+	virtqueue_kick(vq);
+
+	/* When host has read buffer, this completes via balloon_ack */
+	wait_event(vb->acked, virtqueue_get_buf(vq, &unused));
+
+	return 0;
+}
+
 static void set_page_pfns(struct virtio_balloon *vb,
 			  __virtio32 pfns[], struct page *page)
 {
@@ -481,6 +514,7 @@ static int init_vqs(struct virtio_balloon *vb)
 	names[VIRTIO_BALLOON_VQ_STATS] = NULL;
 	callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
 	names[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
+	names[VIRTIO_BALLOON_VQ_REPORTING] = NULL;
 
 	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
 		names[VIRTIO_BALLOON_VQ_STATS] = "stats";
@@ -492,6 +526,11 @@ static int init_vqs(struct virtio_balloon *vb)
 		callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
 	}
 
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) {
+		names[VIRTIO_BALLOON_VQ_REPORTING] = "reporting_vq";
+		callbacks[VIRTIO_BALLOON_VQ_REPORTING] = balloon_ack;
+	}
+
 	err = vb->vdev->config->find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX,
 					 vqs, callbacks, names, NULL, NULL);
 	if (err)
@@ -524,6 +563,9 @@ static int init_vqs(struct virtio_balloon *vb)
 	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
 		vb->free_page_vq = vqs[VIRTIO_BALLOON_VQ_FREE_PAGE];
 
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING))
+		vb->reporting_vq = vqs[VIRTIO_BALLOON_VQ_REPORTING];
+
 	return 0;
 }
 
@@ -953,12 +995,31 @@ static int virtballoon_probe(struct virtio_device *vdev)
 		if (err)
 			goto out_del_balloon_wq;
 	}
+
+	vb->pr_dev_info.report = virtballoon_free_page_report;
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) {
+		unsigned int capacity;
+
+		capacity = virtqueue_get_vring_size(vb->reporting_vq);
+		if (capacity < PAGE_REPORTING_CAPACITY) {
+			err = -ENOSPC;
+			goto out_unregister_shrinker;
+		}
+
+		err = page_reporting_register(&vb->pr_dev_info);
+		if (err)
+			goto out_unregister_shrinker;
+	}
+
 	virtio_device_ready(vdev);
 
 	if (towards_target(vb))
 		virtballoon_changed(vdev);
 	return 0;
 
+out_unregister_shrinker:
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
+		virtio_balloon_unregister_shrinker(vb);
 out_del_balloon_wq:
 	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
 		destroy_workqueue(vb->balloon_wq);
@@ -997,6 +1058,8 @@ static void virtballoon_remove(struct virtio_device *vdev)
 {
 	struct virtio_balloon *vb = vdev->priv;
 
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING))
+		page_reporting_unregister(&vb->pr_dev_info);
 	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
 		virtio_balloon_unregister_shrinker(vb);
 	spin_lock_irq(&vb->stop_update_lock);
@@ -1069,6 +1132,7 @@ static int virtballoon_validate(struct virtio_device *vdev)
 	VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
 	VIRTIO_BALLOON_F_FREE_PAGE_HINT,
 	VIRTIO_BALLOON_F_PAGE_POISON,
+	VIRTIO_BALLOON_F_REPORTING,
 };
 
 static struct virtio_driver virtio_balloon_driver = {
diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
index a1966cd7b677..19974392d324 100644
--- a/include/uapi/linux/virtio_balloon.h
+++ b/include/uapi/linux/virtio_balloon.h
@@ -36,6 +36,7 @@
 #define VIRTIO_BALLOON_F_DEFLATE_ON_OOM	2 /* Deflate balloon on OOM */
 #define VIRTIO_BALLOON_F_FREE_PAGE_HINT	3 /* VQ to report free pages */
 #define VIRTIO_BALLOON_F_PAGE_POISON	4 /* Guest is using page poisoning */
+#define VIRTIO_BALLOON_F_REPORTING	5 /* Page reporting virtqueue */
 
 /* Size of a PFN in the balloon interface. */
 #define VIRTIO_BALLOON_PFN_SHIFT 12


^ permalink raw reply	[flat|nested] 29+ messages in thread

* [PATCH v17 7/9] mm/page_reporting: Rotate reported pages to the tail of the list
  2020-02-11 22:45 [PATCH v17 0/9] mm / virtio: Provide support for free page reporting Alexander Duyck
                   ` (5 preceding siblings ...)
  2020-02-11 22:46 ` [PATCH v17 6/9] virtio-balloon: Add support for providing free page reports to host Alexander Duyck
@ 2020-02-11 22:47 ` Alexander Duyck
  2020-02-19 14:59   ` Mel Gorman
  2020-02-11 22:47 ` [PATCH v17 8/9] mm/page_reporting: Add budget limit on how many pages can be reported per pass Alexander Duyck
                   ` (6 subsequent siblings)
  13 siblings, 1 reply; 29+ messages in thread
From: Alexander Duyck @ 2020-02-11 22:47 UTC (permalink / raw)
  To: kvm, david, mst, linux-kernel, linux-mm, akpm, mgorman
  Cc: yang.zhang.wz, pagupta, konrad.wilk, nitesh, riel, willy,
	lcapitulino, dave.hansen, wei.w.wang, aarcange, pbonzini,
	dan.j.williams, mhocko, alexander.h.duyck, vbabka, osalvador

From: Alexander Duyck <alexander.h.duyck@linux.intel.com>

Rather than walking over the same pages again and again to get to the pages
that have yet to be reported we can save ourselves a significant amount of
time by simply rotating the list so that when we have a full list of
reported pages the head of the list is pointing to the next non-reported
page. Doing this should save us some significant time when processing each
free list.

This doesn't gain us much in the standard case as all of the non-reported
pages should be near the top of the list already. However in the case of
page shuffling this results in a noticeable improvement. Below are the
will-it-scale page_fault1 w/ THP numbers for 16 tasks with and without
this patch.

Without:
tasks   processes       processes_idle  threads         threads_idle
16      8093776.25      0.17            5393242.00      38.20

With:
tasks   processes       processes_idle  threads         threads_idle
16      8283274.75      0.17            5594261.00      38.15

Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
---
 mm/page_reporting.c |   30 ++++++++++++++++++++++--------
 1 file changed, 22 insertions(+), 8 deletions(-)

diff --git a/mm/page_reporting.c b/mm/page_reporting.c
index 1047c6872d4f..6885e74c2367 100644
--- a/mm/page_reporting.c
+++ b/mm/page_reporting.c
@@ -131,17 +131,27 @@ void __page_reporting_notify(void)
 		if (PageReported(page))
 			continue;
 
-		/* Attempt to pull page from list */
-		if (!__isolate_free_page(page, order))
-			break;
+		/* Attempt to pull page from list and place in scatterlist */
+		if (*offset) {
+			if (!__isolate_free_page(page, order)) {
+				next = page;
+				break;
+			}
 
-		/* Add page to scatter list */
-		--(*offset);
-		sg_set_page(&sgl[*offset], page, page_len, 0);
+			/* Add page to scatter list */
+			--(*offset);
+			sg_set_page(&sgl[*offset], page, page_len, 0);
 
-		/* If scatterlist isn't full grab more pages */
-		if (*offset)
 			continue;
+		}
+
+		/*
+		 * Make the first non-processed page in the free list
+		 * the new head of the free list before we release the
+		 * zone lock.
+		 */
+		if (&page->lru != list && !list_is_first(&page->lru, list))
+			list_rotate_to_front(&page->lru, list);
 
 		/* release lock before waiting on report processing */
 		spin_unlock_irq(&zone->lock);
@@ -169,6 +179,10 @@ void __page_reporting_notify(void)
 			break;
 	}
 
+	/* Rotate any leftover pages to the head of the freelist */
+	if (&next->lru != list && !list_is_first(&next->lru, list))
+		list_rotate_to_front(&next->lru, list);
+
 	spin_unlock_irq(&zone->lock);
 
 	return err;


^ permalink raw reply	[flat|nested] 29+ messages in thread

* [PATCH v17 8/9] mm/page_reporting: Add budget limit on how many pages can be reported per pass
  2020-02-11 22:45 [PATCH v17 0/9] mm / virtio: Provide support for free page reporting Alexander Duyck
                   ` (6 preceding siblings ...)
  2020-02-11 22:47 ` [PATCH v17 7/9] mm/page_reporting: Rotate reported pages to the tail of the list Alexander Duyck
@ 2020-02-11 22:47 ` Alexander Duyck
  2020-02-19 15:02   ` Mel Gorman
  2020-02-11 22:47 ` [PATCH v17 9/9] mm/page_reporting: Add free page reporting documentation Alexander Duyck
                   ` (5 subsequent siblings)
  13 siblings, 1 reply; 29+ messages in thread
From: Alexander Duyck @ 2020-02-11 22:47 UTC (permalink / raw)
  To: kvm, david, mst, linux-kernel, linux-mm, akpm, mgorman
  Cc: yang.zhang.wz, pagupta, konrad.wilk, nitesh, riel, willy,
	lcapitulino, dave.hansen, wei.w.wang, aarcange, pbonzini,
	dan.j.williams, mhocko, alexander.h.duyck, vbabka, osalvador

From: Alexander Duyck <alexander.h.duyck@linux.intel.com>

In order to keep ourselves from reporting pages that are just going to be
reused again in the case of heavy churn we can put a limit on how many
total pages we will process per pass. Doing this will allow the worker
thread to go into idle much more quickly so that we avoid competing with
other threads that might be allocating or freeing pages.

The logic added here will limit the worker thread to no more than one
sixteenth of the total free pages in a given area per list. Once that limit
is reached it will update the state so that at the end of the pass we will
reschedule the worker to try again in 2 seconds when the memory churn has
hopefully settled down.

Again this optimization doesn't show much of a benefit in the standard case
as the memory churn is minmal. However with page allocator shuffling
enabled the gain is quite noticeable. Below are the results with a THP
enabled version of the will-it-scale page_fault1 test showing the
improvement in iterations for 16 processes or threads.

Without:
tasks   processes       processes_idle  threads         threads_idle
16      8283274.75      0.17            5594261.00      38.15

With:
tasks   processes       processes_idle  threads         threads_idle
16      8767010.50      0.21            5791312.75      36.98

Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
---
 include/linux/page_reporting.h |    1 +
 mm/page_reporting.c            |   33 ++++++++++++++++++++++++++++++++-
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/include/linux/page_reporting.h b/include/linux/page_reporting.h
index 32355486f572..3b99e0ec24f2 100644
--- a/include/linux/page_reporting.h
+++ b/include/linux/page_reporting.h
@@ -5,6 +5,7 @@
 #include <linux/mmzone.h>
 #include <linux/scatterlist.h>
 
+/* This value should always be a power of 2, see page_reporting_cycle() */
 #define PAGE_REPORTING_CAPACITY		32
 
 struct page_reporting_dev_info {
diff --git a/mm/page_reporting.c b/mm/page_reporting.c
index 6885e74c2367..3bbd471cfc81 100644
--- a/mm/page_reporting.c
+++ b/mm/page_reporting.c
@@ -114,6 +114,7 @@ void __page_reporting_notify(void)
 	struct list_head *list = &area->free_list[mt];
 	unsigned int page_len = PAGE_SIZE << order;
 	struct page *page, *next;
+	long budget;
 	int err = 0;
 
 	/*
@@ -125,12 +126,39 @@ void __page_reporting_notify(void)
 
 	spin_lock_irq(&zone->lock);
 
+	/*
+	 * Limit how many calls we will be making to the page reporting
+	 * device for this list. By doing this we avoid processing any
+	 * given list for too long.
+	 *
+	 * The current value used allows us enough calls to process over a
+	 * sixteenth of the current list plus one additional call to handle
+	 * any pages that may have already been present from the previous
+	 * list processed. This should result in us reporting all pages on
+	 * an idle system in about 30 seconds.
+	 *
+	 * The division here should be cheap since PAGE_REPORTING_CAPACITY
+	 * should always be a power of 2.
+	 */
+	budget = DIV_ROUND_UP(area->nr_free, PAGE_REPORTING_CAPACITY * 16);
+
 	/* loop through free list adding unreported pages to sg list */
 	list_for_each_entry_safe(page, next, list, lru) {
 		/* We are going to skip over the reported pages. */
 		if (PageReported(page))
 			continue;
 
+		/*
+		 * If we fully consumed our budget then update our
+		 * state to indicate that we are requesting additional
+		 * processing and exit this list.
+		 */
+		if (budget < 0) {
+			atomic_set(&prdev->state, PAGE_REPORTING_REQUESTED);
+			next = page;
+			break;
+		}
+
 		/* Attempt to pull page from list and place in scatterlist */
 		if (*offset) {
 			if (!__isolate_free_page(page, order)) {
@@ -146,7 +174,7 @@ void __page_reporting_notify(void)
 		}
 
 		/*
-		 * Make the first non-processed page in the free list
+		 * Make the first non-reported page in the free list
 		 * the new head of the free list before we release the
 		 * zone lock.
 		 */
@@ -162,6 +190,9 @@ void __page_reporting_notify(void)
 		/* reset offset since the full list was reported */
 		*offset = PAGE_REPORTING_CAPACITY;
 
+		/* update budget to reflect call to report function */
+		budget--;
+
 		/* reacquire zone lock and resume processing */
 		spin_lock_irq(&zone->lock);
 


^ permalink raw reply	[flat|nested] 29+ messages in thread

* [PATCH v17 9/9] mm/page_reporting: Add free page reporting documentation
  2020-02-11 22:45 [PATCH v17 0/9] mm / virtio: Provide support for free page reporting Alexander Duyck
                   ` (7 preceding siblings ...)
  2020-02-11 22:47 ` [PATCH v17 8/9] mm/page_reporting: Add budget limit on how many pages can be reported per pass Alexander Duyck
@ 2020-02-11 22:47 ` Alexander Duyck
  2020-02-11 22:51 ` [PATCH v17 QEMU 1/3] virtio-ballon: Implement support for page poison tracking feature Alexander Duyck
                   ` (4 subsequent siblings)
  13 siblings, 0 replies; 29+ messages in thread
From: Alexander Duyck @ 2020-02-11 22:47 UTC (permalink / raw)
  To: kvm, david, mst, linux-kernel, linux-mm, akpm, mgorman
  Cc: yang.zhang.wz, pagupta, konrad.wilk, nitesh, riel, willy,
	lcapitulino, dave.hansen, wei.w.wang, aarcange, pbonzini,
	dan.j.williams, mhocko, alexander.h.duyck, vbabka, osalvador

From: Alexander Duyck <alexander.h.duyck@linux.intel.com>

Add documentation for free page reporting. Currently the only consumer is
virtio-balloon, however it is possible that other drivers might make use of
this so it is best to add a bit of documetation explaining at a high level
how to use the API.

Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
---
 Documentation/vm/free_page_reporting.rst |   41 ++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)
 create mode 100644 Documentation/vm/free_page_reporting.rst

diff --git a/Documentation/vm/free_page_reporting.rst b/Documentation/vm/free_page_reporting.rst
new file mode 100644
index 000000000000..33f54a450a4a
--- /dev/null
+++ b/Documentation/vm/free_page_reporting.rst
@@ -0,0 +1,41 @@
+.. _free_page_reporting:
+
+=====================
+Free Page Reporting
+=====================
+
+Free page reporting is an API by which a device can register to receive
+lists of pages that are currently unused by the system. This is useful in
+the case of virtualization where a guest is then able to use this data to
+notify the hypervisor that it is no longer using certain pages in memory.
+
+For the driver, typically a balloon driver, to use of this functionality
+it will allocate and initialize a page_reporting_dev_info structure. The
+field within the structure it will populate is the "report" function
+pointer used to process the scatterlist. It must also guarantee that it can
+handle at least PAGE_REPORTING_CAPACITY worth of scatterlist entries per
+call to the function. A call to page_reporting_register will register the
+page reporting interface with the reporting framework assuming no other
+page reporting devices are already registered.
+
+Once registered the page reporting API will begin reporting batches of
+pages to the driver. The API will start reporting pages 2 seconds after
+the interface is registered and will continue to do so 2 seconds after any
+page of a sufficiently high order is freed.
+
+Pages reported will be stored in the scatterlist passed to the reporting
+function with the final entry having the end bit set in entry nent - 1.
+While pages are being processed by the report function they will not be
+accessible to the allocator. Once the report function has been completed
+the pages will be returned to the free area from which they were obtained.
+
+Prior to removing a driver that is making use of free page reporting it
+is necessary to call page_reporting_unregister to have the
+page_reporting_dev_info structure that is currently in use by free page
+reporting removed. Doing this will prevent further reports from being
+issued via the interface. If another driver or the same driver is
+registered it is possible for it to resume where the previous driver had
+left off in terms of reporting free pages.
+
+Alexander Duyck, Dec 04, 2019
+


^ permalink raw reply	[flat|nested] 29+ messages in thread

* [PATCH v17 QEMU 1/3] virtio-ballon: Implement support for page poison tracking feature
  2020-02-11 22:45 [PATCH v17 0/9] mm / virtio: Provide support for free page reporting Alexander Duyck
                   ` (8 preceding siblings ...)
  2020-02-11 22:47 ` [PATCH v17 9/9] mm/page_reporting: Add free page reporting documentation Alexander Duyck
@ 2020-02-11 22:51 ` Alexander Duyck
  2020-02-11 22:51 ` [PATCH v17 QEMU 2/3] virtio-balloon: Add support for providing free page reports to host Alexander Duyck
                   ` (3 subsequent siblings)
  13 siblings, 0 replies; 29+ messages in thread
From: Alexander Duyck @ 2020-02-11 22:51 UTC (permalink / raw)
  To: virtio-dev, kvm, mst, david, linux-kernel, linux-mm, akpm
  Cc: yang.zhang.wz, pagupta, konrad.wilk, nitesh, riel, willy,
	lcapitulino, dave.hansen, wei.w.wang, aarcange, pbonzini,
	dan.j.williams, mhocko, mgorman, alexander.h.duyck, vbabka,
	osalvador

From: Alexander Duyck <alexander.h.duyck@linux.intel.com>

We need to make certain to advertise support for page poison tracking if
we want to actually get data on if the guest will be poisoning pages. So
if free page hinting is active we should add page poisoning support and
let the guest disable it if it isn't using it.

Page poisoning will result in a page being dirtied on free. As such we
cannot really avoid having to copy the page at least one more time since
we will need to write the poison value to the destination. As such we can
just ignore free page hinting if page poisoning is enabled as it will
actually reduce the work we have to do.

Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
---
 hw/virtio/virtio-balloon.c         |   25 +++++++++++++++++++++----
 include/hw/virtio/virtio-balloon.h |    1 +
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
index a4729f7fc930..455d85b7082f 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -531,6 +531,15 @@ static void virtio_balloon_free_page_start(VirtIOBalloon *s)
         return;
     }
 
+    /*
+     * If page poisoning is enabled then we probably shouldn't bother with
+     * the hinting since the poisoning will dirty the page and invalidate
+     * the work we are doing anyway.
+     */
+    if (virtio_vdev_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) {
+        return;
+    }
+
     if (s->free_page_report_cmd_id == UINT_MAX) {
         s->free_page_report_cmd_id =
                        VIRTIO_BALLOON_FREE_PAGE_REPORT_CMD_ID_MIN;
@@ -618,12 +627,10 @@ static size_t virtio_balloon_config_size(VirtIOBalloon *s)
     if (s->qemu_4_0_config_size) {
         return sizeof(struct virtio_balloon_config);
     }
-    if (virtio_has_feature(features, VIRTIO_BALLOON_F_PAGE_POISON)) {
+    if (virtio_has_feature(features, VIRTIO_BALLOON_F_PAGE_POISON) ||
+        virtio_has_feature(features, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
         return sizeof(struct virtio_balloon_config);
     }
-    if (virtio_has_feature(features, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
-        return offsetof(struct virtio_balloon_config, poison_val);
-    }
     return offsetof(struct virtio_balloon_config, free_page_report_cmd_id);
 }
 
@@ -634,6 +641,7 @@ static void virtio_balloon_get_config(VirtIODevice *vdev, uint8_t *config_data)
 
     config.num_pages = cpu_to_le32(dev->num_pages);
     config.actual = cpu_to_le32(dev->actual);
+    config.poison_val = cpu_to_le32(dev->poison_val);
 
     if (dev->free_page_report_status == FREE_PAGE_REPORT_S_REQUESTED) {
         config.free_page_report_cmd_id =
@@ -697,6 +705,8 @@ static void virtio_balloon_set_config(VirtIODevice *vdev,
         qapi_event_send_balloon_change(vm_ram_size -
                         ((ram_addr_t) dev->actual << VIRTIO_BALLOON_PFN_SHIFT));
     }
+    dev->poison_val = virtio_vdev_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON) ? 
+                      le32_to_cpu(config.poison_val) : 0;
     trace_virtio_balloon_set_config(dev->actual, oldactual);
 }
 
@@ -706,6 +716,9 @@ static uint64_t virtio_balloon_get_features(VirtIODevice *vdev, uint64_t f,
     VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
     f |= dev->host_features;
     virtio_add_feature(&f, VIRTIO_BALLOON_F_STATS_VQ);
+    if (virtio_has_feature(f, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
+        virtio_add_feature(&f, VIRTIO_BALLOON_F_PAGE_POISON);
+    }
 
     return f;
 }
@@ -854,6 +867,8 @@ static void virtio_balloon_device_reset(VirtIODevice *vdev)
         g_free(s->stats_vq_elem);
         s->stats_vq_elem = NULL;
     }
+
+    s->poison_val = 0;
 }
 
 static void virtio_balloon_set_status(VirtIODevice *vdev, uint8_t status)
@@ -916,6 +931,8 @@ static Property virtio_balloon_properties[] = {
                     VIRTIO_BALLOON_F_DEFLATE_ON_OOM, false),
     DEFINE_PROP_BIT("free-page-hint", VirtIOBalloon, host_features,
                     VIRTIO_BALLOON_F_FREE_PAGE_HINT, false),
+    DEFINE_PROP_BIT("x-page-poison", VirtIOBalloon, host_features,
+                    VIRTIO_BALLOON_F_PAGE_POISON, false),
     /* QEMU 4.0 accidentally changed the config size even when free-page-hint
      * is disabled, resulting in QEMU 3.1 migration incompatibility.  This
      * property retains this quirk for QEMU 4.1 machine types.
diff --git a/include/hw/virtio/virtio-balloon.h b/include/hw/virtio/virtio-balloon.h
index d1c968d2376e..7fe78e5c14d7 100644
--- a/include/hw/virtio/virtio-balloon.h
+++ b/include/hw/virtio/virtio-balloon.h
@@ -70,6 +70,7 @@ typedef struct VirtIOBalloon {
     uint32_t host_features;
 
     bool qemu_4_0_config_size;
+    uint32_t poison_val;
 } VirtIOBalloon;
 
 #endif


^ permalink raw reply	[flat|nested] 29+ messages in thread

* [PATCH v17 QEMU 2/3] virtio-balloon: Add support for providing free page reports to host
  2020-02-11 22:45 [PATCH v17 0/9] mm / virtio: Provide support for free page reporting Alexander Duyck
                   ` (9 preceding siblings ...)
  2020-02-11 22:51 ` [PATCH v17 QEMU 1/3] virtio-ballon: Implement support for page poison tracking feature Alexander Duyck
@ 2020-02-11 22:51 ` Alexander Duyck
  2020-02-11 22:51 ` [PATCH v17 QEMU 3/3] virtio-balloon: Provide a interface for free page reporting Alexander Duyck
                   ` (2 subsequent siblings)
  13 siblings, 0 replies; 29+ messages in thread
From: Alexander Duyck @ 2020-02-11 22:51 UTC (permalink / raw)
  To: virtio-dev, kvm, mst, david, linux-kernel, linux-mm, akpm
  Cc: yang.zhang.wz, pagupta, konrad.wilk, nitesh, riel, willy,
	lcapitulino, dave.hansen, wei.w.wang, aarcange, pbonzini,
	dan.j.williams, mhocko, mgorman, alexander.h.duyck, vbabka,
	osalvador

From: Alexander Duyck <alexander.h.duyck@linux.intel.com>

Add support for the page reporting feature provided by virtio-balloon.
Reporting differs from the regular balloon functionality in that is is
much less durable than a standard memory balloon. Instead of creating a
list of pages that cannot be accessed the pages are only inaccessible
while they are being indicated to the virtio interface. Once the
interface has acknowledged them they are placed back into their respective
free lists and are once again accessible by the guest system.

Unlike a standard balloon we don't inflate and deflate the pages. Instead
we perform the reporting, and once the reporting is completed it is
assumed that the page has been dropped from the guest and will be faulted
back in the next time the page is accessed.

This patch is a subset of the UAPI patch that was submitted for the Linux
kernel. The original patch can be found at:
https://lore.kernel.org/lkml/20200211224657.29318.68624.stgit@localhost.localdomain/

Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
---
 include/standard-headers/linux/virtio_balloon.h |    1 +
 1 file changed, 1 insertion(+)

diff --git a/include/standard-headers/linux/virtio_balloon.h b/include/standard-headers/linux/virtio_balloon.h
index 9375ca2a70de..1c5f6d6f2de6 100644
--- a/include/standard-headers/linux/virtio_balloon.h
+++ b/include/standard-headers/linux/virtio_balloon.h
@@ -36,6 +36,7 @@
 #define VIRTIO_BALLOON_F_DEFLATE_ON_OOM	2 /* Deflate balloon on OOM */
 #define VIRTIO_BALLOON_F_FREE_PAGE_HINT	3 /* VQ to report free pages */
 #define VIRTIO_BALLOON_F_PAGE_POISON	4 /* Guest is using page poisoning */
+#define VIRTIO_BALLOON_F_REPORTING	5 /* Page reporting virtqueue */
 
 /* Size of a PFN in the balloon interface. */
 #define VIRTIO_BALLOON_PFN_SHIFT 12


^ permalink raw reply	[flat|nested] 29+ messages in thread

* [PATCH v17 QEMU 3/3] virtio-balloon: Provide a interface for free page reporting
  2020-02-11 22:45 [PATCH v17 0/9] mm / virtio: Provide support for free page reporting Alexander Duyck
                   ` (10 preceding siblings ...)
  2020-02-11 22:51 ` [PATCH v17 QEMU 2/3] virtio-balloon: Add support for providing free page reports to host Alexander Duyck
@ 2020-02-11 22:51 ` Alexander Duyck
  2020-02-11 22:53 ` [PATCH v17 QEMU 4/3 RFC] memory: Add support for MADV_FREE as mechanism to lazy discard pages Alexander Duyck
  2020-02-11 23:05 ` [PATCH v17 0/9] mm / virtio: Provide support for free page reporting Andrew Morton
  13 siblings, 0 replies; 29+ messages in thread
From: Alexander Duyck @ 2020-02-11 22:51 UTC (permalink / raw)
  To: virtio-dev, kvm, mst, david, linux-kernel, linux-mm, akpm
  Cc: yang.zhang.wz, pagupta, konrad.wilk, nitesh, riel, willy,
	lcapitulino, dave.hansen, wei.w.wang, aarcange, pbonzini,
	dan.j.williams, mhocko, mgorman, alexander.h.duyck, vbabka,
	osalvador

From: Alexander Duyck <alexander.h.duyck@linux.intel.com>

Add support for what I am referring to as "free page reporting".
Basically the idea is to function very similar to how the balloon works
in that we basically end up madvising the page as not being used. However
we don't really need to bother with any deflate type logic since the page
will be faulted back into the guest when it is read or written to.

This is meant to be a simplification of the existing balloon interface
to use for providing hints to what memory needs to be freed. I am assuming
this is safe to do as the deflate logic does not actually appear to do very
much other than tracking what subpages have been released and which ones
haven't.

Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
---
 hw/virtio/virtio-balloon.c         |   46 ++++++++++++++++++++++++++++++++++--
 include/hw/virtio/virtio-balloon.h |    2 +-
 2 files changed, 45 insertions(+), 3 deletions(-)

diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
index 455d85b7082f..5faafd2f62ac 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -321,6 +321,40 @@ static void balloon_stats_set_poll_interval(Object *obj, Visitor *v,
     balloon_stats_change_timer(s, 0);
 }
 
+static void virtio_balloon_handle_report(VirtIODevice *vdev, VirtQueue *vq)
+{
+    VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
+    VirtQueueElement *elem;
+
+    while ((elem = virtqueue_pop(vq, sizeof(VirtQueueElement)))) {
+    	unsigned int i;
+
+        for (i = 0; i < elem->in_num; i++) {
+            void *addr = elem->in_sg[i].iov_base;
+            size_t size = elem->in_sg[i].iov_len;
+            ram_addr_t ram_offset;
+            size_t rb_page_size;
+            RAMBlock *rb;
+
+            if (qemu_balloon_is_inhibited() || dev->poison_val)
+                continue;
+
+            rb = qemu_ram_block_from_host(addr, false, &ram_offset);
+            rb_page_size = qemu_ram_pagesize(rb);
+
+            /* For now we will simply ignore unaligned memory regions */
+            if ((ram_offset | size) & (rb_page_size - 1))
+                continue;
+
+            ram_block_discard_range(rb, ram_offset, size);
+        }
+
+        virtqueue_push(vq, elem, 0);
+        virtio_notify(vdev, vq);
+        g_free(elem);
+    }
+}
+
 static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq)
 {
     VirtIOBalloon *s = VIRTIO_BALLOON(vdev);
@@ -628,7 +662,8 @@ static size_t virtio_balloon_config_size(VirtIOBalloon *s)
         return sizeof(struct virtio_balloon_config);
     }
     if (virtio_has_feature(features, VIRTIO_BALLOON_F_PAGE_POISON) ||
-        virtio_has_feature(features, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
+        virtio_has_feature(features, VIRTIO_BALLOON_F_FREE_PAGE_HINT) ||
+        virtio_has_feature(features, VIRTIO_BALLOON_F_REPORTING)) {
         return sizeof(struct virtio_balloon_config);
     }
     return offsetof(struct virtio_balloon_config, free_page_report_cmd_id);
@@ -716,7 +751,8 @@ static uint64_t virtio_balloon_get_features(VirtIODevice *vdev, uint64_t f,
     VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
     f |= dev->host_features;
     virtio_add_feature(&f, VIRTIO_BALLOON_F_STATS_VQ);
-    if (virtio_has_feature(f, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
+    if (virtio_has_feature(f, VIRTIO_BALLOON_F_FREE_PAGE_HINT) ||
+        virtio_has_feature(f, VIRTIO_BALLOON_F_REPORTING)) {
         virtio_add_feature(&f, VIRTIO_BALLOON_F_PAGE_POISON);
     }
 
@@ -806,6 +842,10 @@ static void virtio_balloon_device_realize(DeviceState *dev, Error **errp)
     s->dvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output);
     s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats);
 
+    if (virtio_has_feature(s->host_features, VIRTIO_BALLOON_F_REPORTING)) {
+        s->rvq = virtio_add_queue(vdev, 32, virtio_balloon_handle_report);
+    }
+
     if (virtio_has_feature(s->host_features,
                            VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
         s->free_page_vq = virtio_add_queue(vdev, VIRTQUEUE_MAX_SIZE,
@@ -939,6 +979,8 @@ static Property virtio_balloon_properties[] = {
      */
     DEFINE_PROP_BOOL("qemu-4-0-config-size", VirtIOBalloon,
                      qemu_4_0_config_size, false),
+    DEFINE_PROP_BIT("unused-page-reporting", VirtIOBalloon, host_features,
+                    VIRTIO_BALLOON_F_REPORTING, true),
     DEFINE_PROP_LINK("iothread", VirtIOBalloon, iothread, TYPE_IOTHREAD,
                      IOThread *),
     DEFINE_PROP_END_OF_LIST(),
diff --git a/include/hw/virtio/virtio-balloon.h b/include/hw/virtio/virtio-balloon.h
index 7fe78e5c14d7..db5bf7127112 100644
--- a/include/hw/virtio/virtio-balloon.h
+++ b/include/hw/virtio/virtio-balloon.h
@@ -42,7 +42,7 @@ enum virtio_balloon_free_page_report_status {
 
 typedef struct VirtIOBalloon {
     VirtIODevice parent_obj;
-    VirtQueue *ivq, *dvq, *svq, *free_page_vq;
+    VirtQueue *ivq, *dvq, *svq, *free_page_vq, *rvq;
     uint32_t free_page_report_status;
     uint32_t num_pages;
     uint32_t actual;


^ permalink raw reply	[flat|nested] 29+ messages in thread

* [PATCH v17 QEMU 4/3 RFC] memory: Add support for MADV_FREE as mechanism to lazy discard pages
  2020-02-11 22:45 [PATCH v17 0/9] mm / virtio: Provide support for free page reporting Alexander Duyck
                   ` (11 preceding siblings ...)
  2020-02-11 22:51 ` [PATCH v17 QEMU 3/3] virtio-balloon: Provide a interface for free page reporting Alexander Duyck
@ 2020-02-11 22:53 ` Alexander Duyck
  2020-02-11 23:05 ` [PATCH v17 0/9] mm / virtio: Provide support for free page reporting Andrew Morton
  13 siblings, 0 replies; 29+ messages in thread
From: Alexander Duyck @ 2020-02-11 22:53 UTC (permalink / raw)
  To: virtio-dev, kvm, mst, david, linux-kernel, linux-mm, akpm
  Cc: yang.zhang.wz, pagupta, konrad.wilk, nitesh, riel, willy,
	lcapitulino, dave.hansen, wei.w.wang, aarcange, pbonzini,
	dan.j.williams, mhocko, mgorman, alexander.h.duyck, vbabka,
	osalvador

From: Alexander Duyck <alexander.h.duyck@linux.intel.com>

Add support for the MADV_FREE advice argument when discarding pages.
Specifically we add an option to perform a lazy discard for use with free
page reporting as this allows us to avoid expensive page zeroing in the
case that the system is not under memory pressure.

To enable this I simply extended the ram_block_discard_range function to
add an extra parameter for "lazy" freeing. I then renamed the function,
wrapped it in a function defined using the original name and defaulting
lazy to false. From there I created a second wrapper for
ram_block_free_range and updated the page reporting code to use that.

Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
---
 exec.c                     |   39 +++++++++++++++++++++++++++------------
 hw/virtio/virtio-balloon.c |    2 +-
 include/exec/cpu-common.h  |    1 +
 3 files changed, 29 insertions(+), 13 deletions(-)

diff --git a/exec.c b/exec.c
index 67e520d18ea5..2266574eb06e 100644
--- a/exec.c
+++ b/exec.c
@@ -3881,15 +3881,8 @@ int qemu_ram_foreach_block(RAMBlockIterFunc func, void *opaque)
     return ret;
 }
 
-/*
- * Unmap pages of memory from start to start+length such that
- * they a) read as 0, b) Trigger whatever fault mechanism
- * the OS provides for postcopy.
- * The pages must be unmapped by the end of the function.
- * Returns: 0 on success, none-0 on failure
- *
- */
-int ram_block_discard_range(RAMBlock *rb, uint64_t start, size_t length)
+static int __ram_block_discard_range(RAMBlock *rb, uint64_t start,
+                                     size_t length, bool lazy)
 {
     int ret = -1;
 
@@ -3941,13 +3934,18 @@ int ram_block_discard_range(RAMBlock *rb, uint64_t start, size_t length)
 #endif
         }
         if (need_madvise) {
-            /* For normal RAM this causes it to be unmapped,
+#ifdef CONFIG_MADVISE
+#ifdef MADV_FREE
+            int advice = (lazy && !need_fallocate) ? MADV_FREE : MADV_DONTNEED;
+#else
+            int advice = MADV_DONTNEED;
+#endif
+            /* For normal RAM this causes it to be lazy freed or unmapped,
              * for shared memory it causes the local mapping to disappear
              * and to fall back on the file contents (which we just
              * fallocate'd away).
              */
-#if defined(CONFIG_MADVISE)
-            ret =  madvise(host_startaddr, length, MADV_DONTNEED);
+            ret =  madvise(host_startaddr, length, advice);
             if (ret) {
                 ret = -errno;
                 error_report("ram_block_discard_range: Failed to discard range "
@@ -3975,6 +3973,23 @@ err:
     return ret;
 }
 
+/*
+ * Unmap pages of memory from start to start+length such that
+ * they a) read as 0, b) Trigger whatever fault mechanism
+ * the OS provides for postcopy.
+ * The pages must be unmapped by the end of the function.
+ * Returns: 0 on success, none-0 on failure
+ *
+ */
+int ram_block_discard_range(RAMBlock *rb, uint64_t start, size_t length)
+{
+    return __ram_block_discard_range(rb, start, length, false);
+}
+
+int ram_block_free_range(RAMBlock *rb, uint64_t start, size_t length)
+{
+    return __ram_block_discard_range(rb, start, length, true);
+}
 bool ramblock_is_pmem(RAMBlock *rb)
 {
     return rb->flags & RAM_PMEM;
diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
index 5faafd2f62ac..7df92af73792 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -346,7 +346,7 @@ static void virtio_balloon_handle_report(VirtIODevice *vdev, VirtQueue *vq)
             if ((ram_offset | size) & (rb_page_size - 1))
                 continue;
 
-            ram_block_discard_range(rb, ram_offset, size);
+            ram_block_free_range(rb, ram_offset, size);
         }
 
         virtqueue_push(vq, elem, 0);
diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h
index 81753bbb3431..2bbd26784c63 100644
--- a/include/exec/cpu-common.h
+++ b/include/exec/cpu-common.h
@@ -104,6 +104,7 @@ typedef int (RAMBlockIterFunc)(RAMBlock *rb, void *opaque);
 
 int qemu_ram_foreach_block(RAMBlockIterFunc func, void *opaque);
 int ram_block_discard_range(RAMBlock *rb, uint64_t start, size_t length);
+int ram_block_free_range(RAMBlock *rb, uint64_t start, size_t length);
 
 #endif
 


^ permalink raw reply	[flat|nested] 29+ messages in thread

* Re: [PATCH v17 0/9] mm / virtio: Provide support for free page reporting
  2020-02-11 22:45 [PATCH v17 0/9] mm / virtio: Provide support for free page reporting Alexander Duyck
                   ` (12 preceding siblings ...)
  2020-02-11 22:53 ` [PATCH v17 QEMU 4/3 RFC] memory: Add support for MADV_FREE as mechanism to lazy discard pages Alexander Duyck
@ 2020-02-11 23:05 ` Andrew Morton
  2020-02-11 23:55   ` Alexander Duyck
  13 siblings, 1 reply; 29+ messages in thread
From: Andrew Morton @ 2020-02-11 23:05 UTC (permalink / raw)
  To: Alexander Duyck
  Cc: kvm, david, mst, linux-kernel, linux-mm, mgorman, yang.zhang.wz,
	pagupta, konrad.wilk, nitesh, riel, willy, lcapitulino,
	dave.hansen, wei.w.wang, aarcange, pbonzini, dan.j.williams,
	mhocko, alexander.h.duyck, vbabka, osalvador

On Tue, 11 Feb 2020 14:45:51 -0800 Alexander Duyck <alexander.duyck@gmail.com> wrote:

> This series provides an asynchronous means of reporting free guest pages
> to a hypervisor so that the memory associated with those pages can be
> dropped and reused by other processes and/or guests on the host. Using
> this it is possible to avoid unnecessary I/O to disk and greatly improve
> performance in the case of memory overcommit on the host.

"greatly improve" sounds nice.

> When enabled we will be performing a scan of free memory every 2 seconds
> while pages of sufficiently high order are being freed. In each pass at
> least one sixteenth of each free list will be reported. By doing this we
> avoid racing against other threads that may be causing a high amount of
> memory churn.
> 
> The lowest page order currently scanned when reporting pages is
> pageblock_order so that this feature will not interfere with the use of
> Transparent Huge Pages in the case of virtualization.
> 
> Currently this is only in use by virtio-balloon however there is the hope
> that at some point in the future other hypervisors might be able to make
> use of it. In the virtio-balloon/QEMU implementation the hypervisor is
> currently using MADV_DONTNEED to indicate to the host kernel that the page
> is currently free. It will be zeroed and faulted back into the guest the
> next time the page is accessed.
> 
> To track if a page is reported or not the Uptodate flag was repurposed and
> used as a Reported flag for Buddy pages. We walk though the free list
> isolating pages and adding them to the scatterlist until we either
> encounter the end of the list or have processed at least one sixteenth of
> the pages that were listed in nr_free prior to us starting. If we fill the
> scatterlist before we reach the end of the list we rotate the list so that
> the first unreported page we encounter is moved to the head of the list as
> that is where we will resume after we have freed the reported pages back
> into the tail of the list.
> 
> Below are the results from various benchmarks. I primarily focused on two
> tests. The first is the will-it-scale/page_fault2 test, and the other is
> a modified version of will-it-scale/page_fault1 that was enabled to use
> THP. I did this as it allows for better visibility into different parts
> of the memory subsystem. The guest is running with 32G for RAM on one
> node of a E5-2630 v3. The host has had some features such as CPU turbo
> disabled in the BIOS.
> 
> Test                   page_fault1 (THP)    page_fault2
> Name            tasks  Process Iter  STDEV  Process Iter  STDEV
> Baseline            1    1012402.50  0.14%     361855.25  0.81%
>                    16    8827457.25  0.09%    3282347.00  0.34%
> 
> Patches Applied     1    1007897.00  0.23%     361887.00  0.26%
>                    16    8784741.75  0.39%    3240669.25  0.48%
> 
> Patches Enabled     1    1010227.50  0.39%     359749.25  0.56%
>                    16    8756219.00  0.24%    3226608.75  0.97%
> 
> Patches Enabled     1    1050982.00  4.26%     357966.25  0.14%
>  page shuffle      16    8672601.25  0.49%    3223177.75  0.40%
> 
> Patches enabled     1    1003238.00  0.22%     360211.00  0.22%
>  shuffle w/ RFC    16    8767010.50  0.32%    3199874.00  0.71%

But these differences seem really small - around 1%?  I think we're
just showing not much harm was caused?

> The results above are for a baseline with a linux-next-20191219 kernel,
> that kernel with this patch set applied but page reporting disabled in
> virtio-balloon, the patches applied and page reporting fully enabled, the
> patches enabled with page shuffling enabled, and the patches applied with
> page shuffling enabled and an RFC patch that makes used of MADV_FREE in
> QEMU. These results include the deviation seen between the average value
> reported here versus the high and/or low value. I observed that during the
> test memory usage for the first three tests never dropped whereas with the
> patches fully enabled the VM would drop to using only a few GB of the
> host's memory when switching from memhog to page fault tests.

And this is the "great improvement", yes?

Is it possible to measure the end-user-visible benefits of this?

> Any of the overhead visible with this patch set enabled seems due to page
> faults caused by accessing the reported pages and the host zeroing the page
> before giving it back to the guest. This overhead is much more visible when
> using THP than with standard 4K pages. In addition page shuffling seemed to
> increase the amount of faults generated due to an increase in memory churn.
> The overehad is reduced when using MADV_FREE as we can avoid the extra
> zeroing of the pages when they are reintroduced to the host, as can be seen
> when the RFC is applied with shuffling enabled.
> 
> The overall guest size is kept fairly small to only a few GB while the test
> is running. If the host memory were oversubscribed this patch set should
> result in a performance improvement as swapping memory in the host can be
> avoided.

"should result".  Can we firm this up a lot?

^ permalink raw reply	[flat|nested] 29+ messages in thread

* Re: [PATCH v17 0/9] mm / virtio: Provide support for free page reporting
  2020-02-11 23:05 ` [PATCH v17 0/9] mm / virtio: Provide support for free page reporting Andrew Morton
@ 2020-02-11 23:55   ` Alexander Duyck
  2020-02-12  0:19     ` Andrew Morton
  0 siblings, 1 reply; 29+ messages in thread
From: Alexander Duyck @ 2020-02-11 23:55 UTC (permalink / raw)
  To: Andrew Morton, Alexander Duyck
  Cc: kvm, david, mst, linux-kernel, linux-mm, mgorman, yang.zhang.wz,
	pagupta, konrad.wilk, nitesh, riel, willy, lcapitulino,
	dave.hansen, wei.w.wang, aarcange, pbonzini, dan.j.williams,
	mhocko, vbabka, osalvador

On Tue, 2020-02-11 at 15:05 -0800, Andrew Morton wrote:
> On Tue, 11 Feb 2020 14:45:51 -0800 Alexander Duyck <alexander.duyck@gmail.com> wrote:
> 
> > This series provides an asynchronous means of reporting free guest pages
> > to a hypervisor so that the memory associated with those pages can be
> > dropped and reused by other processes and/or guests on the host. Using
> > this it is possible to avoid unnecessary I/O to disk and greatly improve
> > performance in the case of memory overcommit on the host.
> 
> "greatly improve" sounds nice.
> 
> > When enabled we will be performing a scan of free memory every 2 seconds
> > while pages of sufficiently high order are being freed. In each pass at
> > least one sixteenth of each free list will be reported. By doing this we
> > avoid racing against other threads that may be causing a high amount of
> > memory churn.
> > 
> > The lowest page order currently scanned when reporting pages is
> > pageblock_order so that this feature will not interfere with the use of
> > Transparent Huge Pages in the case of virtualization.
> > 
> > Currently this is only in use by virtio-balloon however there is the hope
> > that at some point in the future other hypervisors might be able to make
> > use of it. In the virtio-balloon/QEMU implementation the hypervisor is
> > currently using MADV_DONTNEED to indicate to the host kernel that the page
> > is currently free. It will be zeroed and faulted back into the guest the
> > next time the page is accessed.
> > 
> > To track if a page is reported or not the Uptodate flag was repurposed and
> > used as a Reported flag for Buddy pages. We walk though the free list
> > isolating pages and adding them to the scatterlist until we either
> > encounter the end of the list or have processed at least one sixteenth of
> > the pages that were listed in nr_free prior to us starting. If we fill the
> > scatterlist before we reach the end of the list we rotate the list so that
> > the first unreported page we encounter is moved to the head of the list as
> > that is where we will resume after we have freed the reported pages back
> > into the tail of the list.
> > 
> > Below are the results from various benchmarks. I primarily focused on two
> > tests. The first is the will-it-scale/page_fault2 test, and the other is
> > a modified version of will-it-scale/page_fault1 that was enabled to use
> > THP. I did this as it allows for better visibility into different parts
> > of the memory subsystem. The guest is running with 32G for RAM on one
> > node of a E5-2630 v3. The host has had some features such as CPU turbo
> > disabled in the BIOS.
> > 
> > Test                   page_fault1 (THP)    page_fault2
> > Name            tasks  Process Iter  STDEV  Process Iter  STDEV
> > Baseline            1    1012402.50  0.14%     361855.25  0.81%
> >                    16    8827457.25  0.09%    3282347.00  0.34%
> > 
> > Patches Applied     1    1007897.00  0.23%     361887.00  0.26%
> >                    16    8784741.75  0.39%    3240669.25  0.48%
> > 
> > Patches Enabled     1    1010227.50  0.39%     359749.25  0.56%
> >                    16    8756219.00  0.24%    3226608.75  0.97%
> > 
> > Patches Enabled     1    1050982.00  4.26%     357966.25  0.14%
> >  page shuffle      16    8672601.25  0.49%    3223177.75  0.40%
> > 
> > Patches enabled     1    1003238.00  0.22%     360211.00  0.22%
> >  shuffle w/ RFC    16    8767010.50  0.32%    3199874.00  0.71%
> 
> But these differences seem really small - around 1%?  I think we're
> just showing not much harm was caused?

Yes. Basically I am just showing the iterations are not negatively
impacted. The big difference between the cases where it is enabled versus
the cases where it is not is that the guest memory footprint is much
smaller in the enabled cases than in the baseline or "Applied" cases.

> > The results above are for a baseline with a linux-next-20191219 kernel,
> > that kernel with this patch set applied but page reporting disabled in
> > virtio-balloon, the patches applied and page reporting fully enabled, the
> > patches enabled with page shuffling enabled, and the patches applied with
> > page shuffling enabled and an RFC patch that makes used of MADV_FREE in
> > QEMU. These results include the deviation seen between the average value
> > reported here versus the high and/or low value. I observed that during the
> > test memory usage for the first three tests never dropped whereas with the
> > patches fully enabled the VM would drop to using only a few GB of the
> > host's memory when switching from memhog to page fault tests.
> 
> And this is the "great improvement", yes?

Yes, this is the great improvement. Basically what we get is effectively
auto-ballooning so the guests aren't having to go to swap when they start
to get loaded up since they are returning the memory to the host when they
are done with it.

> Is it possible to measure the end-user-visible benefits of this?

If I clear the page cache on my host via drop_caches, fire up my 32G VM,
and run the following commands:
  memhog 32g
  echo 3 > /proc/sys/vm/drop_caches

On the host I just have to monitor /proc/meminfo and I can see the
difference. I get the following results on the host, in the enabled case
it takes about 30 seconds for it to settle into the final state since I
only report page a bit at a time:
Baseline/Applied
  MemTotal:    131963012 kB
  MemFree:      95189740 kB

Enabled:
  MemTotal:    131963012 kB
  MemFree:     126459472 kB

This is what I was referring to with the comment above. I had a test I was
running back around the first RFC that consisted of bringing up enough VMs
so that there was a bit of memory overcommit and then having the VMs in
turn run memhog. As I recall the difference between the two was  something
like a couple minutes to run through all the VMs as the memhog would take
up to 40+ seconds for one that was having to pull from swap while it took
only 5 to 7 seconds for the VMs that were all running the page hinting.

I had referenced it here in the RFC:
https://lore.kernel.org/lkml/20190204181118.12095.38300.stgit@localhost.localdomain/

I have been verifying the memory has been getting freed but didn't feel
like the test added much value so I haven't added it to the cover page for
a while since the time could vary widely and is dependent on things like
the disk type used for the host swap since my SSD is likely faster than
spinning rust, but may not be as fast as other SSDs on the market. Since
the disk speed can play such a huge role I wasn't comfortable posting
numbers since the benefits could vary so widely.

> > Any of the overhead visible with this patch set enabled seems due to page
> > faults caused by accessing the reported pages and the host zeroing the page
> > before giving it back to the guest. This overhead is much more visible when
> > using THP than with standard 4K pages. In addition page shuffling seemed to
> > increase the amount of faults generated due to an increase in memory churn.
> > The overehad is reduced when using MADV_FREE as we can avoid the extra
> > zeroing of the pages when they are reintroduced to the host, as can be seen
> > when the RFC is applied with shuffling enabled.
> > 
> > The overall guest size is kept fairly small to only a few GB while the test
> > is running. If the host memory were oversubscribed this patch set should
> > result in a performance improvement as swapping memory in the host can be
> > avoided.
> 
> "should result".  Can we firm this up a lot?

I said "should result" here because if the guests are using all of their
memory then the free page reporting won't make a difference since you have
to have free pages before they can be reported. Also we cannot use free
page reporting in the cases such as when a device is direct assigned into
the guest as that currently prevents us from disassociating a page from
the guest.





^ permalink raw reply	[flat|nested] 29+ messages in thread

* Re: [PATCH v17 0/9] mm / virtio: Provide support for free page reporting
  2020-02-11 23:55   ` Alexander Duyck
@ 2020-02-12  0:19     ` Andrew Morton
  2020-02-12  1:19       ` Alexander Duyck
  2020-02-18 16:37       ` Alexander Duyck
  0 siblings, 2 replies; 29+ messages in thread
From: Andrew Morton @ 2020-02-12  0:19 UTC (permalink / raw)
  To: Alexander Duyck
  Cc: Alexander Duyck, kvm, david, mst, linux-kernel, linux-mm,
	mgorman, yang.zhang.wz, pagupta, konrad.wilk, nitesh, riel,
	willy, lcapitulino, dave.hansen, wei.w.wang, aarcange, pbonzini,
	dan.j.williams, mhocko, vbabka, osalvador

On Tue, 11 Feb 2020 15:55:31 -0800 Alexander Duyck <alexander.h.duyck@linux.intel.com> wrote:

> On the host I just have to monitor /proc/meminfo and I can see the
> difference. I get the following results on the host, in the enabled case
> it takes about 30 seconds for it to settle into the final state since I
> only report page a bit at a time:
> Baseline/Applied
>   MemTotal:    131963012 kB
>   MemFree:      95189740 kB
> 
> Enabled:
>   MemTotal:    131963012 kB
>   MemFree:     126459472 kB
> 
> This is what I was referring to with the comment above. I had a test I was
> running back around the first RFC that consisted of bringing up enough VMs
> so that there was a bit of memory overcommit and then having the VMs in
> turn run memhog. As I recall the difference between the two was  something
> like a couple minutes to run through all the VMs as the memhog would take
> up to 40+ seconds for one that was having to pull from swap while it took
> only 5 to 7 seconds for the VMs that were all running the page hinting.
> 
> I had referenced it here in the RFC:
> https://lore.kernel.org/lkml/20190204181118.12095.38300.stgit@localhost.localdomain/
> 
> I have been verifying the memory has been getting freed but didn't feel
> like the test added much value so I haven't added it to the cover page for
> a while since the time could vary widely and is dependent on things like
> the disk type used for the host swap since my SSD is likely faster than
> spinning rust, but may not be as fast as other SSDs on the market. Since
> the disk speed can play such a huge role I wasn't comfortable posting
> numbers since the benefits could vary so widely.

OK, thanks.  I'll add the patches to the mm pile.  The new
mm/page_reporting.c is unreviewed afaict, so I guess you own that for
now ;)

It would be very nice to get some feedback from testers asserting "yes,
this really helped my workload" but I understand this sort of testing
is hard to obtain at this stage.


^ permalink raw reply	[flat|nested] 29+ messages in thread

* Re: [PATCH v17 0/9] mm / virtio: Provide support for free page reporting
  2020-02-12  0:19     ` Andrew Morton
@ 2020-02-12  1:19       ` Alexander Duyck
  2020-02-18 16:37       ` Alexander Duyck
  1 sibling, 0 replies; 29+ messages in thread
From: Alexander Duyck @ 2020-02-12  1:19 UTC (permalink / raw)
  To: Andrew Morton
  Cc: Alexander Duyck, kvm list, David Hildenbrand, Michael S. Tsirkin,
	LKML, linux-mm, Mel Gorman, Yang Zhang, Pankaj Gupta,
	Konrad Rzeszutek Wilk, Nitesh Narayan Lal, Rik van Riel,
	Matthew Wilcox, lcapitulino, Dave Hansen, Wang, Wei W,
	Andrea Arcangeli, Paolo Bonzini, Dan Williams, Michal Hocko,
	Vlastimil Babka, Oscar Salvador

On Tue, Feb 11, 2020 at 4:19 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Tue, 11 Feb 2020 15:55:31 -0800 Alexander Duyck <alexander.h.duyck@linux.intel.com> wrote:
>
> > On the host I just have to monitor /proc/meminfo and I can see the
> > difference. I get the following results on the host, in the enabled case
> > it takes about 30 seconds for it to settle into the final state since I
> > only report page a bit at a time:
> > Baseline/Applied
> >   MemTotal:    131963012 kB
> >   MemFree:      95189740 kB
> >
> > Enabled:
> >   MemTotal:    131963012 kB
> >   MemFree:     126459472 kB
> >
> > This is what I was referring to with the comment above. I had a test I was
> > running back around the first RFC that consisted of bringing up enough VMs
> > so that there was a bit of memory overcommit and then having the VMs in
> > turn run memhog. As I recall the difference between the two was  something
> > like a couple minutes to run through all the VMs as the memhog would take
> > up to 40+ seconds for one that was having to pull from swap while it took
> > only 5 to 7 seconds for the VMs that were all running the page hinting.
> >
> > I had referenced it here in the RFC:
> > https://lore.kernel.org/lkml/20190204181118.12095.38300.stgit@localhost.localdomain/
> >
> > I have been verifying the memory has been getting freed but didn't feel
> > like the test added much value so I haven't added it to the cover page for
> > a while since the time could vary widely and is dependent on things like
> > the disk type used for the host swap since my SSD is likely faster than
> > spinning rust, but may not be as fast as other SSDs on the market. Since
> > the disk speed can play such a huge role I wasn't comfortable posting
> > numbers since the benefits could vary so widely.
>
> OK, thanks.  I'll add the patches to the mm pile.  The new
> mm/page_reporting.c is unreviewed afaict, so I guess you own that for
> now ;)

I will see what I can do to get some additional review of those
patches. There has been some review, but I rewrote that block after
suggestions as I had to split it out over several patches to account
for the gains from the changes in patches 7 and 8.

> It would be very nice to get some feedback from testers asserting "yes,
> this really helped my workload" but I understand this sort of testing
> is hard to obtain at this stage.

Without the QEMU patches applied there isn't much that this patch set
can do on its own, so that is another piece I have to work on. Yet
another reason to make sure it does no harm if it is not enabled.

So far the one that surprised me the most is that somebody from Huawei
was working to add device pass-thru support to it already.
https://lore.kernel.org/lkml/1578408399-20092-1-git-send-email-weiqi4@huawei.com/

Thanks.

- Alex

^ permalink raw reply	[flat|nested] 29+ messages in thread

* Re: [PATCH v17 0/9] mm / virtio: Provide support for free page reporting
  2020-02-12  0:19     ` Andrew Morton
  2020-02-12  1:19       ` Alexander Duyck
@ 2020-02-18 16:37       ` Alexander Duyck
  2020-02-19  8:49         ` Mel Gorman
  2020-02-19 15:06         ` Mel Gorman
  1 sibling, 2 replies; 29+ messages in thread
From: Alexander Duyck @ 2020-02-18 16:37 UTC (permalink / raw)
  To: mgorman
  Cc: Andrew Morton, Alexander Duyck, kvm, david, mst, linux-kernel,
	linux-mm, yang.zhang.wz, pagupta, konrad.wilk, nitesh, riel,
	willy, lcapitulino, dave.hansen, wei.w.wang, aarcange, pbonzini,
	dan.j.williams, mhocko, vbabka, osalvador

On Tue, 2020-02-11 at 16:19 -0800, Andrew Morton wrote:
> On Tue, 11 Feb 2020 15:55:31 -0800 Alexander Duyck <alexander.h.duyck@linux.intel.com> wrote:
> 
> > On the host I just have to monitor /proc/meminfo and I can see the
> > difference. I get the following results on the host, in the enabled case
> > it takes about 30 seconds for it to settle into the final state since I
> > only report page a bit at a time:
> > Baseline/Applied
> >   MemTotal:    131963012 kB
> >   MemFree:      95189740 kB
> > 
> > Enabled:
> >   MemTotal:    131963012 kB
> >   MemFree:     126459472 kB
> > 
> > This is what I was referring to with the comment above. I had a test I was
> > running back around the first RFC that consisted of bringing up enough VMs
> > so that there was a bit of memory overcommit and then having the VMs in
> > turn run memhog. As I recall the difference between the two was  something
> > like a couple minutes to run through all the VMs as the memhog would take
> > up to 40+ seconds for one that was having to pull from swap while it took
> > only 5 to 7 seconds for the VMs that were all running the page hinting.
> > 
> > I had referenced it here in the RFC:
> > https://lore.kernel.org/lkml/20190204181118.12095.38300.stgit@localhost.localdomain/
> > 
> > I have been verifying the memory has been getting freed but didn't feel
> > like the test added much value so I haven't added it to the cover page for
> > a while since the time could vary widely and is dependent on things like
> > the disk type used for the host swap since my SSD is likely faster than
> > spinning rust, but may not be as fast as other SSDs on the market. Since
> > the disk speed can play such a huge role I wasn't comfortable posting
> > numbers since the benefits could vary so widely.
> 
> OK, thanks.  I'll add the patches to the mm pile.  The new
> mm/page_reporting.c is unreviewed afaict, so I guess you own that for
> now ;)
> 
> It would be very nice to get some feedback from testers asserting "yes,
> this really helped my workload" but I understand this sort of testing
> is hard to obtain at this stage.
> 

Mel,

Any ETA on when you would be available to review these patches? They are
now in Andrew's tree and in linux-next. I am hoping to get any remaining
review from the community sorted out in the next few weeks so I can move
onto focusing on how best to exert pressure on the page cache so that we
can keep the guest memory footprint small.

Thanks.

- Alex


^ permalink raw reply	[flat|nested] 29+ messages in thread

* Re: [PATCH v17 0/9] mm / virtio: Provide support for free page reporting
  2020-02-18 16:37       ` Alexander Duyck
@ 2020-02-19  8:49         ` Mel Gorman
  2020-02-19 15:06         ` Mel Gorman
  1 sibling, 0 replies; 29+ messages in thread
From: Mel Gorman @ 2020-02-19  8:49 UTC (permalink / raw)
  To: Alexander Duyck
  Cc: Andrew Morton, Alexander Duyck, kvm, david, mst, linux-kernel,
	linux-mm, yang.zhang.wz, pagupta, konrad.wilk, nitesh, riel,
	willy, lcapitulino, dave.hansen, wei.w.wang, aarcange, pbonzini,
	dan.j.williams, mhocko, vbabka, osalvador

On Tue, Feb 18, 2020 at 08:37:46AM -0800, Alexander Duyck wrote:
> On Tue, 2020-02-11 at 16:19 -0800, Andrew Morton wrote:
> > On Tue, 11 Feb 2020 15:55:31 -0800 Alexander Duyck <alexander.h.duyck@linux.intel.com> wrote:
> > 
> > > On the host I just have to monitor /proc/meminfo and I can see the
> > > difference. I get the following results on the host, in the enabled case
> > > it takes about 30 seconds for it to settle into the final state since I
> > > only report page a bit at a time:
> > > Baseline/Applied
> > >   MemTotal:    131963012 kB
> > >   MemFree:      95189740 kB
> > > 
> > > Enabled:
> > >   MemTotal:    131963012 kB
> > >   MemFree:     126459472 kB
> > > 
> > > This is what I was referring to with the comment above. I had a test I was
> > > running back around the first RFC that consisted of bringing up enough VMs
> > > so that there was a bit of memory overcommit and then having the VMs in
> > > turn run memhog. As I recall the difference between the two was  something
> > > like a couple minutes to run through all the VMs as the memhog would take
> > > up to 40+ seconds for one that was having to pull from swap while it took
> > > only 5 to 7 seconds for the VMs that were all running the page hinting.
> > > 
> > > I had referenced it here in the RFC:
> > > https://lore.kernel.org/lkml/20190204181118.12095.38300.stgit@localhost.localdomain/
> > > 
> > > I have been verifying the memory has been getting freed but didn't feel
> > > like the test added much value so I haven't added it to the cover page for
> > > a while since the time could vary widely and is dependent on things like
> > > the disk type used for the host swap since my SSD is likely faster than
> > > spinning rust, but may not be as fast as other SSDs on the market. Since
> > > the disk speed can play such a huge role I wasn't comfortable posting
> > > numbers since the benefits could vary so widely.
> > 
> > OK, thanks.  I'll add the patches to the mm pile.  The new
> > mm/page_reporting.c is unreviewed afaict, so I guess you own that for
> > now ;)
> > 
> > It would be very nice to get some feedback from testers asserting "yes,
> > this really helped my workload" but I understand this sort of testing
> > is hard to obtain at this stage.
> > 
> 
> Mel,
> 
> Any ETA on when you would be available to review these patches? They are
> now in Andrew's tree and in linux-next. I am hoping to get any remaining
> review from the community sorted out in the next few weeks so I can move
> onto focusing on how best to exert pressure on the page cache so that we
> can keep the guest memory footprint small.
> 

I hope to get to it soon. I'm trying to finalise a scheduler-related
series that reconciles NUMA and CPU balancing and it's occupying much of
my attention available for mainline development :(

-- 
Mel Gorman
SUSE Labs

^ permalink raw reply	[flat|nested] 29+ messages in thread

* Re: [PATCH v17 3/9] mm: Add function __putback_isolated_page
  2020-02-11 22:46 ` [PATCH v17 3/9] mm: Add function __putback_isolated_page Alexander Duyck
@ 2020-02-19 14:33   ` Mel Gorman
  0 siblings, 0 replies; 29+ messages in thread
From: Mel Gorman @ 2020-02-19 14:33 UTC (permalink / raw)
  To: Alexander Duyck
  Cc: kvm, david, mst, linux-kernel, linux-mm, akpm, yang.zhang.wz,
	pagupta, konrad.wilk, nitesh, riel, willy, lcapitulino,
	dave.hansen, wei.w.wang, aarcange, pbonzini, dan.j.williams,
	mhocko, alexander.h.duyck, vbabka, osalvador

On Tue, Feb 11, 2020 at 02:46:24PM -0800, Alexander Duyck wrote:
> From: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> 
> There are cases where we would benefit from avoiding having to go through
> the allocation and free cycle to return an isolated page.
> 
> Examples for this might include page poisoning in which we isolate a page
> and then put it back in the free list without ever having actually
> allocated it.
> 
> This will enable us to also avoid notifiers for the future free page
> reporting which will need to avoid retriggering page reporting when
> returning pages that have been reported on.
> 
> Acked-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>

Ok, the prior code that used post_alloc_hook to make the isolated page seem
like a normally allocated page followed by a free seems strange anyway. As
well as being expensive, isolated pages can end up on the per-cpu lists
which is probably not what is desired. I *think* what you've done is ok so

Acked-by: Mel Gorman <mgorman@techsingularity.net>

-- 
Mel Gorman
SUSE Labs

^ permalink raw reply	[flat|nested] 29+ messages in thread

* Re: [PATCH v17 4/9] mm: Introduce Reported pages
  2020-02-11 22:46 ` [PATCH v17 4/9] mm: Introduce Reported pages Alexander Duyck
@ 2020-02-19 14:55   ` Mel Gorman
  2020-02-20 18:44     ` Alexander Duyck
  0 siblings, 1 reply; 29+ messages in thread
From: Mel Gorman @ 2020-02-19 14:55 UTC (permalink / raw)
  To: Alexander Duyck
  Cc: kvm, david, mst, linux-kernel, linux-mm, akpm, yang.zhang.wz,
	pagupta, konrad.wilk, nitesh, riel, willy, lcapitulino,
	dave.hansen, wei.w.wang, aarcange, pbonzini, dan.j.williams,
	mhocko, alexander.h.duyck, vbabka, osalvador

On Tue, Feb 11, 2020 at 02:46:35PM -0800, Alexander Duyck wrote:
> diff --git a/mm/page_reporting.c b/mm/page_reporting.c
> new file mode 100644
> index 000000000000..1047c6872d4f
> --- /dev/null
> +++ b/mm/page_reporting.c
> @@ -0,0 +1,319 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/mm.h>
> +#include <linux/mmzone.h>
> +#include <linux/page_reporting.h>
> +#include <linux/gfp.h>
> +#include <linux/export.h>
> +#include <linux/delay.h>
> +#include <linux/scatterlist.h>
> +
> +#include "page_reporting.h"
> +#include "internal.h"
> +
> +#define PAGE_REPORTING_DELAY	(2 * HZ)

I assume there is nothing special about 2 seconds other than "do some
progress every so often".

> +static struct page_reporting_dev_info __rcu *pr_dev_info __read_mostly;
> +
> +enum {
> +	PAGE_REPORTING_IDLE = 0,
> +	PAGE_REPORTING_REQUESTED,
> +	PAGE_REPORTING_ACTIVE
> +};
> +
> +/* request page reporting */
> +static void
> +__page_reporting_request(struct page_reporting_dev_info *prdev)
> +{
> +	unsigned int state;
> +
> +	/* Check to see if we are in desired state */
> +	state = atomic_read(&prdev->state);
> +	if (state == PAGE_REPORTING_REQUESTED)
> +		return;
> +
> +	/*
> +	 *  If reporting is already active there is nothing we need to do.
> +	 *  Test against 0 as that represents PAGE_REPORTING_IDLE.
> +	 */
> +	state = atomic_xchg(&prdev->state, PAGE_REPORTING_REQUESTED);
> +	if (state != PAGE_REPORTING_IDLE)
> +		return;
> +
> +	/*
> +	 * Delay the start of work to allow a sizable queue to build. For
> +	 * now we are limiting this to running no more than once every
> +	 * couple of seconds.
> +	 */
> +	schedule_delayed_work(&prdev->work, PAGE_REPORTING_DELAY);
> +}

Seems a fair use of atomics.

> +static int
> +page_reporting_cycle(struct page_reporting_dev_info *prdev, struct zone *zone,
> +		     unsigned int order, unsigned int mt,
> +		     struct scatterlist *sgl, unsigned int *offset)
> +{
> +	struct free_area *area = &zone->free_area[order];
> +	struct list_head *list = &area->free_list[mt];
> +	unsigned int page_len = PAGE_SIZE << order;
> +	struct page *page, *next;
> +	int err = 0;
> +
> +	/*
> +	 * Perform early check, if free area is empty there is
> +	 * nothing to process so we can skip this free_list.
> +	 */
> +	if (list_empty(list))
> +		return err;
> +
> +	spin_lock_irq(&zone->lock);
> +
> +	/* loop through free list adding unreported pages to sg list */
> +	list_for_each_entry_safe(page, next, list, lru) {
> +		/* We are going to skip over the reported pages. */
> +		if (PageReported(page))
> +			continue;
> +
> +		/* Attempt to pull page from list */
> +		if (!__isolate_free_page(page, order))
> +			break;
> +

Might want to note that you are breaking because the only reason to fail
the isolation is that watermarks are not met and we are likely under
memory pressure. It's not a big issue.

However, while I think this is correct, it's hard to follow. This loop can
be broken out of with pages still on the scatter gather list. The current
flow guarantees that err will not be set at this point so the caller
cleans it up so we always drain the list either here or in the caller.

While I think it works, it's a bit fragile. I recommend putting a comment
above this noting why it's safe and put a VM_WARN_ON_ONCE(err) before the
break in case someone tries to change this in a years time and does not
spot that the flow to reach page_reporting_drain *somewhere* is critical.

> +		/* Add page to scatter list */
> +		--(*offset);
> +		sg_set_page(&sgl[*offset], page, page_len, 0);
> +
> +		/* If scatterlist isn't full grab more pages */
> +		if (*offset)
> +			continue;
> +
> +		/* release lock before waiting on report processing */
> +		spin_unlock_irq(&zone->lock);
> +
> +		/* begin processing pages in local list */
> +		err = prdev->report(prdev, sgl, PAGE_REPORTING_CAPACITY);
> +
> +		/* reset offset since the full list was reported */
> +		*offset = PAGE_REPORTING_CAPACITY;
> +
> +		/* reacquire zone lock and resume processing */
> +		spin_lock_irq(&zone->lock);
> +
> +		/* flush reported pages from the sg list */
> +		page_reporting_drain(prdev, sgl, PAGE_REPORTING_CAPACITY, !err);
> +
> +		/*
> +		 * Reset next to first entry, the old next isn't valid
> +		 * since we dropped the lock to report the pages
> +		 */
> +		next = list_first_entry(list, struct page, lru);
> +
> +		/* exit on error */
> +		if (err)
> +			break;
> +	}
> +
> +	spin_unlock_irq(&zone->lock);
> +
> +	return err;
> +}

I complained about the use of zone lock before but in this version, I
think I'm ok with it. The lock is held for the free list manipulations
which is what it's for. The state management with atomics seems
reasonable.

Otherwise I think this is ok and I think the implementation right. Of
great importance to me was the allocator fast paths but they seem to be
adequately protected by a static branch so

Acked-by: Mel Gorman <mgorman@techsingularity.net>

The ack applies regardless of whether you decide to document and
defensively protect page_reporting_cycle against losing pages on the
scatter/gather list but I do recommend it.

-- 
Mel Gorman
SUSE Labs

^ permalink raw reply	[flat|nested] 29+ messages in thread

* Re: [PATCH v17 7/9] mm/page_reporting: Rotate reported pages to the tail of the list
  2020-02-11 22:47 ` [PATCH v17 7/9] mm/page_reporting: Rotate reported pages to the tail of the list Alexander Duyck
@ 2020-02-19 14:59   ` Mel Gorman
  0 siblings, 0 replies; 29+ messages in thread
From: Mel Gorman @ 2020-02-19 14:59 UTC (permalink / raw)
  To: Alexander Duyck
  Cc: kvm, david, mst, linux-kernel, linux-mm, akpm, yang.zhang.wz,
	pagupta, konrad.wilk, nitesh, riel, willy, lcapitulino,
	dave.hansen, wei.w.wang, aarcange, pbonzini, dan.j.williams,
	mhocko, alexander.h.duyck, vbabka, osalvador

On Tue, Feb 11, 2020 at 02:47:08PM -0800, Alexander Duyck wrote:
> From: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> 
> Rather than walking over the same pages again and again to get to the pages
> that have yet to be reported we can save ourselves a significant amount of
> time by simply rotating the list so that when we have a full list of
> reported pages the head of the list is pointing to the next non-reported
> page. Doing this should save us some significant time when processing each
> free list.
> 
> This doesn't gain us much in the standard case as all of the non-reported
> pages should be near the top of the list already. However in the case of
> page shuffling this results in a noticeable improvement. Below are the
> will-it-scale page_fault1 w/ THP numbers for 16 tasks with and without
> this patch.
> 
> Without:
> tasks   processes       processes_idle  threads         threads_idle
> 16      8093776.25      0.17            5393242.00      38.20
> 
> With:
> tasks   processes       processes_idle  threads         threads_idle
> 16      8283274.75      0.17            5594261.00      38.15
> 
> Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>

Thanks for pulling this patch out and noting its impact. I think the
rotation is ok and if it turns out I missed something, it'll be
relatively easy to back out just the optimisation and leave the rest of
the feature intact.

Acked-by: Mel Gorman <mgorman@techsingularity.net>

-- 
Mel Gorman
SUSE Labs

^ permalink raw reply	[flat|nested] 29+ messages in thread

* Re: [PATCH v17 8/9] mm/page_reporting: Add budget limit on how many pages can be reported per pass
  2020-02-11 22:47 ` [PATCH v17 8/9] mm/page_reporting: Add budget limit on how many pages can be reported per pass Alexander Duyck
@ 2020-02-19 15:02   ` Mel Gorman
  0 siblings, 0 replies; 29+ messages in thread
From: Mel Gorman @ 2020-02-19 15:02 UTC (permalink / raw)
  To: Alexander Duyck
  Cc: kvm, david, mst, linux-kernel, linux-mm, akpm, yang.zhang.wz,
	pagupta, konrad.wilk, nitesh, riel, willy, lcapitulino,
	dave.hansen, wei.w.wang, aarcange, pbonzini, dan.j.williams,
	mhocko, alexander.h.duyck, vbabka, osalvador

On Tue, Feb 11, 2020 at 02:47:19PM -0800, Alexander Duyck wrote:
> From: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> 
> In order to keep ourselves from reporting pages that are just going to be
> reused again in the case of heavy churn we can put a limit on how many
> total pages we will process per pass. Doing this will allow the worker
> thread to go into idle much more quickly so that we avoid competing with
> other threads that might be allocating or freeing pages.
> 
> The logic added here will limit the worker thread to no more than one
> sixteenth of the total free pages in a given area per list. Once that limit
> is reached it will update the state so that at the end of the pass we will
> reschedule the worker to try again in 2 seconds when the memory churn has
> hopefully settled down.
> 
> Again this optimization doesn't show much of a benefit in the standard case
> as the memory churn is minmal. However with page allocator shuffling
> enabled the gain is quite noticeable. Below are the results with a THP
> enabled version of the will-it-scale page_fault1 test showing the
> improvement in iterations for 16 processes or threads.
> 
> Without:
> tasks   processes       processes_idle  threads         threads_idle
> 16      8283274.75      0.17            5594261.00      38.15
> 
> With:
> tasks   processes       processes_idle  threads         threads_idle
> 16      8767010.50      0.21            5791312.75      36.98
> 
> Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>

Seems fair. The test case you used would have been pounding on the zone
lock at fairly high frequency so it represents a worst-case scenario but
not necessarily an unrealistic one

Acked-by: Mel Gorman <mgorman@techsingularity.net>

-- 
Mel Gorman
SUSE Labs

^ permalink raw reply	[flat|nested] 29+ messages in thread

* Re: [PATCH v17 0/9] mm / virtio: Provide support for free page reporting
  2020-02-18 16:37       ` Alexander Duyck
  2020-02-19  8:49         ` Mel Gorman
@ 2020-02-19 15:06         ` Mel Gorman
  1 sibling, 0 replies; 29+ messages in thread
From: Mel Gorman @ 2020-02-19 15:06 UTC (permalink / raw)
  To: Alexander Duyck
  Cc: Andrew Morton, Alexander Duyck, kvm, david, mst, linux-kernel,
	linux-mm, yang.zhang.wz, pagupta, konrad.wilk, nitesh, riel,
	willy, lcapitulino, dave.hansen, wei.w.wang, aarcange, pbonzini,
	dan.j.williams, mhocko, vbabka, osalvador

On Tue, Feb 18, 2020 at 08:37:46AM -0800, Alexander Duyck wrote:
> On Tue, 2020-02-11 at 16:19 -0800, Andrew Morton wrote:
> > On Tue, 11 Feb 2020 15:55:31 -0800 Alexander Duyck <alexander.h.duyck@linux.intel.com> wrote:
> > 
> > > On the host I just have to monitor /proc/meminfo and I can see the
> > > difference. I get the following results on the host, in the enabled case
> > > it takes about 30 seconds for it to settle into the final state since I
> > > only report page a bit at a time:
> > > Baseline/Applied
> > >   MemTotal:    131963012 kB
> > >   MemFree:      95189740 kB
> > > 
> > > Enabled:
> > >   MemTotal:    131963012 kB
> > >   MemFree:     126459472 kB
> > > 
> > > This is what I was referring to with the comment above. I had a test I was
> > > running back around the first RFC that consisted of bringing up enough VMs
> > > so that there was a bit of memory overcommit and then having the VMs in
> > > turn run memhog. As I recall the difference between the two was  something
> > > like a couple minutes to run through all the VMs as the memhog would take
> > > up to 40+ seconds for one that was having to pull from swap while it took
> > > only 5 to 7 seconds for the VMs that were all running the page hinting.
> > > 
> > > I had referenced it here in the RFC:
> > > https://lore.kernel.org/lkml/20190204181118.12095.38300.stgit@localhost.localdomain/
> > > 
> > > I have been verifying the memory has been getting freed but didn't feel
> > > like the test added much value so I haven't added it to the cover page for
> > > a while since the time could vary widely and is dependent on things like
> > > the disk type used for the host swap since my SSD is likely faster than
> > > spinning rust, but may not be as fast as other SSDs on the market. Since
> > > the disk speed can play such a huge role I wasn't comfortable posting
> > > numbers since the benefits could vary so widely.
> > 
> > OK, thanks.  I'll add the patches to the mm pile.  The new
> > mm/page_reporting.c is unreviewed afaict, so I guess you own that for
> > now ;)
> > 
> > It would be very nice to get some feedback from testers asserting "yes,
> > this really helped my workload" but I understand this sort of testing
> > is hard to obtain at this stage.
> > 
> 
> Mel,
> 
> Any ETA on when you would be available to review these patches? They are
> now in Andrew's tree and in linux-next. I am hoping to get any remaining
> review from the community sorted out in the next few weeks so I can move
> onto focusing on how best to exert pressure on the page cache so that we
> can keep the guest memory footprint small.
> 

Sorry for the delay but I got through most of the patches -- I ignored
the qemu ones. Overall I think it's fine, while I made a suggestion on
how one section can be a bit more defensive, I don't consider it
mandatory to update the series.

Last time I got upset by the use of zone lock, premature optimisation and
some potential page allocator overhead. Now how you use the zone lock is
justified and I think the state managed by atomics is ok. The optimisations
are split out and so if there is a bug lurking in there, they can be
backed out relatively easily and it was easier to review the series in
this way. Finally, the overhead to the page allocator when the feature
is disabled should be non-existent as it's protected by a static branch
so I have no further objections.

Thanks!

-- 
Mel Gorman
SUSE Labs

^ permalink raw reply	[flat|nested] 29+ messages in thread

* Re: [PATCH v17 4/9] mm: Introduce Reported pages
  2020-02-19 14:55   ` Mel Gorman
@ 2020-02-20 18:44     ` Alexander Duyck
  2020-02-20 22:35       ` Mel Gorman
  0 siblings, 1 reply; 29+ messages in thread
From: Alexander Duyck @ 2020-02-20 18:44 UTC (permalink / raw)
  To: Mel Gorman, Alexander Duyck
  Cc: kvm, david, mst, linux-kernel, linux-mm, akpm, yang.zhang.wz,
	pagupta, konrad.wilk, nitesh, riel, willy, lcapitulino,
	dave.hansen, wei.w.wang, aarcange, pbonzini, dan.j.williams,
	mhocko, vbabka, osalvador

On Wed, 2020-02-19 at 14:55 +0000, Mel Gorman wrote:
> On Tue, Feb 11, 2020 at 02:46:35PM -0800, Alexander Duyck wrote:
> > diff --git a/mm/page_reporting.c b/mm/page_reporting.c
> > new file mode 100644
> > index 000000000000..1047c6872d4f
> > --- /dev/null
> > +++ b/mm/page_reporting.c
> > @@ -0,0 +1,319 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +#include <linux/mm.h>
> > +#include <linux/mmzone.h>
> > +#include <linux/page_reporting.h>
> > +#include <linux/gfp.h>
> > +#include <linux/export.h>
> > +#include <linux/delay.h>
> > +#include <linux/scatterlist.h>
> > +
> > +#include "page_reporting.h"
> > +#include "internal.h"
> > +
> > +#define PAGE_REPORTING_DELAY	(2 * HZ)
> 
> I assume there is nothing special about 2 seconds other than "do some
> progress every so often".

Yes, nothing special. I played around with a few different values. I just
settled on 2 seconds as I figured with that and 1/16 of the list per pass
it came out to about 30 seconds which I felt is about the right time for a
fully utilized system to settle back to the inactive state.


> > 
> > +static int
> > +page_reporting_cycle(struct page_reporting_dev_info *prdev, struct zone *zone,
> > +		     unsigned int order, unsigned int mt,
> > +		     struct scatterlist *sgl, unsigned int *offset)
> > +{
> > +	struct free_area *area = &zone->free_area[order];
> > +	struct list_head *list = &area->free_list[mt];
> > +	unsigned int page_len = PAGE_SIZE << order;
> > +	struct page *page, *next;
> > +	int err = 0;
> > +
> > +	/*
> > +	 * Perform early check, if free area is empty there is
> > +	 * nothing to process so we can skip this free_list.
> > +	 */
> > +	if (list_empty(list))
> > +		return err;
> > +
> > +	spin_lock_irq(&zone->lock);
> > +
> > +	/* loop through free list adding unreported pages to sg list */
> > +	list_for_each_entry_safe(page, next, list, lru) {
> > +		/* We are going to skip over the reported pages. */
> > +		if (PageReported(page))
> > +			continue;
> > +
> > +		/* Attempt to pull page from list */
> > +		if (!__isolate_free_page(page, order))
> > +			break;
> > +
> 
> Might want to note that you are breaking because the only reason to fail
> the isolation is that watermarks are not met and we are likely under
> memory pressure. It's not a big issue.
> 
> However, while I think this is correct, it's hard to follow. This loop can
> be broken out of with pages still on the scatter gather list. The current
> flow guarantees that err will not be set at this point so the caller
> cleans it up so we always drain the list either here or in the caller.

I can probably submit a follow-up patch to update the comments. The reason
for not returning an error is because I didn't consider it an error that
we encountered the watermark and were not able to pull any more pages.
Instead I considered that the "stop" point for this pass and have it just
exit out of the loop and flush the data.

At the start of the next pass we will check against the low watermark
instead of the minimum watermark and if that check fails we will simply
stop reporting pages for the zone until additional pages are freed.

I can probably also update the description for page_reporting_cycle since
it may not be clear that the output for this is a partially filled in-
progress scatterlist so we always have to reporting any remaining entries
at the end of processing a given zone. It might make more sense if I move
the bits related to "leftover" in page_reporting_process_zone into their
own function.

> While I think it works, it's a bit fragile. I recommend putting a comment
> above this noting why it's safe and put a VM_WARN_ON_ONCE(err) before the
> break in case someone tries to change this in a years time and does not
> spot that the flow to reach page_reporting_drain *somewhere* is critical.

I assume this isn't about this section, but the section below?

> > +		/* Add page to scatter list */
> > +		--(*offset);
> > +		sg_set_page(&sgl[*offset], page, page_len, 0);
> > +
> > +		/* If scatterlist isn't full grab more pages */
> > +		if (*offset)
> > +			continue;
> > +
> > +		/* release lock before waiting on report processing */
> > +		spin_unlock_irq(&zone->lock);
> > +
> > +		/* begin processing pages in local list */
> > +		err = prdev->report(prdev, sgl, PAGE_REPORTING_CAPACITY);
> > +

So one thing I can do is probably add a comment here as well to more
thoroughly explain the reason why we wait to call the break until we are
in the block below.

> > +		/* reset offset since the full list was reported */
> > +		*offset = PAGE_REPORTING_CAPACITY;
> > +
> > +		/* reacquire zone lock and resume processing */
> > +		spin_lock_irq(&zone->lock);
> > +
> > +		/* flush reported pages from the sg list */
> > +		page_reporting_drain(prdev, sgl, PAGE_REPORTING_CAPACITY, !err);
> > +
> > +		/*
> > +		 * Reset next to first entry, the old next isn't valid
> > +		 * since we dropped the lock to report the pages
> > +		 */
> > +		next = list_first_entry(list, struct page, lru);
> > +
> > +		/* exit on error */
> > +		if (err)
> > +			break;

And I assume you meant to add the VM_WARN_ON_ONCE here? The statement
above wouldn't make much sense since err would always be 0.

> > +	}
> > +
> > +	spin_unlock_irq(&zone->lock);
> > +
> > +	return err;
> > +}
> 
> I complained about the use of zone lock before but in this version, I
> think I'm ok with it. The lock is held for the free list manipulations
> which is what it's for. The state management with atomics seems
> reasonable.
> 
> Otherwise I think this is ok and I think the implementation right. Of
> great importance to me was the allocator fast paths but they seem to be
> adequately protected by a static branch so
> 
> Acked-by: Mel Gorman <mgorman@techsingularity.net>
> 
> The ack applies regardless of whether you decide to document and
> defensively protect page_reporting_cycle against losing pages on the
> scatter/gather list but I do recommend it.

Thanks for reviewing this. I appreciate the feedback.

- Alex



^ permalink raw reply	[flat|nested] 29+ messages in thread

* Re: [PATCH v17 4/9] mm: Introduce Reported pages
  2020-02-20 18:44     ` Alexander Duyck
@ 2020-02-20 22:35       ` Mel Gorman
  2020-02-21 19:25         ` Alexander Duyck
  0 siblings, 1 reply; 29+ messages in thread
From: Mel Gorman @ 2020-02-20 22:35 UTC (permalink / raw)
  To: Alexander Duyck
  Cc: Alexander Duyck, kvm, david, mst, linux-kernel, linux-mm, akpm,
	yang.zhang.wz, pagupta, konrad.wilk, nitesh, riel, willy,
	lcapitulino, dave.hansen, wei.w.wang, aarcange, pbonzini,
	dan.j.williams, mhocko, vbabka, osalvador

On Thu, Feb 20, 2020 at 10:44:21AM -0800, Alexander Duyck wrote:
> > > +static int
> > > +page_reporting_cycle(struct page_reporting_dev_info *prdev, struct zone *zone,
> > > +		     unsigned int order, unsigned int mt,
> > > +		     struct scatterlist *sgl, unsigned int *offset)
> > > +{
> > > +	struct free_area *area = &zone->free_area[order];
> > > +	struct list_head *list = &area->free_list[mt];
> > > +	unsigned int page_len = PAGE_SIZE << order;
> > > +	struct page *page, *next;
> > > +	int err = 0;
> > > +
> > > +	/*
> > > +	 * Perform early check, if free area is empty there is
> > > +	 * nothing to process so we can skip this free_list.
> > > +	 */
> > > +	if (list_empty(list))
> > > +		return err;
> > > +
> > > +	spin_lock_irq(&zone->lock);
> > > +
> > > +	/* loop through free list adding unreported pages to sg list */
> > > +	list_for_each_entry_safe(page, next, list, lru) {
> > > +		/* We are going to skip over the reported pages. */
> > > +		if (PageReported(page))
> > > +			continue;
> > > +
> > > +		/* Attempt to pull page from list */
> > > +		if (!__isolate_free_page(page, order))
> > > +			break;
> > > +
> > 
> > Might want to note that you are breaking because the only reason to fail
> > the isolation is that watermarks are not met and we are likely under
> > memory pressure. It's not a big issue.
> > 
> > However, while I think this is correct, it's hard to follow. This loop can
> > be broken out of with pages still on the scatter gather list. The current
> > flow guarantees that err will not be set at this point so the caller
> > cleans it up so we always drain the list either here or in the caller.
> 
> I can probably submit a follow-up patch to update the comments. The reason
> for not returning an error is because I didn't consider it an error that
> we encountered the watermark and were not able to pull any more pages.
> Instead I considered that the "stop" point for this pass and have it just
> exit out of the loop and flush the data.
> 

I don't consider it an error and I don't think you should return an
error. The comment just needs to explain that the draining happens in
the caller in this case. That should be enough of a warning to a future
developer to double check the flow after any changes to make sure the
drain is reached.

> > While I think it works, it's a bit fragile. I recommend putting a comment
> > above this noting why it's safe and put a VM_WARN_ON_ONCE(err) before the
> > break in case someone tries to change this in a years time and does not
> > spot that the flow to reach page_reporting_drain *somewhere* is critical.
> 
> I assume this isn't about this section, but the section below?
> 

I meant something like

if (!__isolate_free_page(page, order)) {
	VM_WARN_ON_ONCE(err);
	break;
}

Because at this point it's possible there are entries that should go
through page_reporting_drain() but the caller will not call
page_reporting_drain() in the event of an error.

-- 
Mel Gorman
SUSE Labs

^ permalink raw reply	[flat|nested] 29+ messages in thread

* Re: [PATCH v17 4/9] mm: Introduce Reported pages
  2020-02-20 22:35       ` Mel Gorman
@ 2020-02-21 19:25         ` Alexander Duyck
  2020-02-21 20:19           ` Mel Gorman
  0 siblings, 1 reply; 29+ messages in thread
From: Alexander Duyck @ 2020-02-21 19:25 UTC (permalink / raw)
  To: Mel Gorman
  Cc: Alexander Duyck, kvm, david, mst, linux-kernel, linux-mm, akpm,
	yang.zhang.wz, pagupta, konrad.wilk, nitesh, riel, willy,
	lcapitulino, dave.hansen, wei.w.wang, aarcange, pbonzini,
	dan.j.williams, mhocko, vbabka, osalvador

On Thu, 2020-02-20 at 22:35 +0000, Mel Gorman wrote:
> On Thu, Feb 20, 2020 at 10:44:21AM -0800, Alexander Duyck wrote:
> > > > +static int
> > > > +page_reporting_cycle(struct page_reporting_dev_info *prdev, struct zone *zone,
> > > > +		     unsigned int order, unsigned int mt,
> > > > +		     struct scatterlist *sgl, unsigned int *offset)
> > > > +{
> > > > +	struct free_area *area = &zone->free_area[order];
> > > > +	struct list_head *list = &area->free_list[mt];
> > > > +	unsigned int page_len = PAGE_SIZE << order;
> > > > +	struct page *page, *next;
> > > > +	int err = 0;
> > > > +
> > > > +	/*
> > > > +	 * Perform early check, if free area is empty there is
> > > > +	 * nothing to process so we can skip this free_list.
> > > > +	 */
> > > > +	if (list_empty(list))
> > > > +		return err;
> > > > +
> > > > +	spin_lock_irq(&zone->lock);
> > > > +
> > > > +	/* loop through free list adding unreported pages to sg list */
> > > > +	list_for_each_entry_safe(page, next, list, lru) {
> > > > +		/* We are going to skip over the reported pages. */
> > > > +		if (PageReported(page))
> > > > +			continue;
> > > > +
> > > > +		/* Attempt to pull page from list */
> > > > +		if (!__isolate_free_page(page, order))
> > > > +			break;
> > > > +
> > > 
> > > Might want to note that you are breaking because the only reason to fail
> > > the isolation is that watermarks are not met and we are likely under
> > > memory pressure. It's not a big issue.
> > > 
> > > However, while I think this is correct, it's hard to follow. This loop can
> > > be broken out of with pages still on the scatter gather list. The current
> > > flow guarantees that err will not be set at this point so the caller
> > > cleans it up so we always drain the list either here or in the caller.
> > 
> > I can probably submit a follow-up patch to update the comments. The reason
> > for not returning an error is because I didn't consider it an error that
> > we encountered the watermark and were not able to pull any more pages.
> > Instead I considered that the "stop" point for this pass and have it just
> > exit out of the loop and flush the data.
> > 
> 
> I don't consider it an error and I don't think you should return an
> error. The comment just needs to explain that the draining happens in
> the caller in this case. That should be enough of a warning to a future
> developer to double check the flow after any changes to make sure the
> drain is reached.

The comment I can do, that shouldn't be an issue. The point I was getting
at is that a separate drain call is expected for this any time the
function is not returning an error, and the only way it can return an
error is if there was a reporting issue.

> > > While I think it works, it's a bit fragile. I recommend putting a comment
> > > above this noting why it's safe and put a VM_WARN_ON_ONCE(err) before the
> > > break in case someone tries to change this in a years time and does not
> > > spot that the flow to reach page_reporting_drain *somewhere* is critical.
> > 
> > I assume this isn't about this section, but the section below?
> > 
> 
> I meant something like
> 
> if (!__isolate_free_page(page, order)) {
> 	VM_WARN_ON_ONCE(err);
> 	break;
> }
> 
> Because at this point it's possible there are entries that should go
> through page_reporting_drain() but the caller will not call
> page_reporting_drain() in the event of an error.

I would think adding that would confuse things even more. There is a break
statement at the end of the loop that will break out if err is set. So we
should never hit the VM_WARN_ON_ONCE because err should always be 0 before
we even attempt to isolate the page. I think something like the following
would probably make more sense:

        err = page_reporting_cycle(prdev, zone, order, mt,
                                   sgl, &offset);
        if (err) {
                /*
                 * We should have drained the scatterlist
                 * prior to exiting page_reporting_cycle if
                 * we encountered an error. If we did not
                 * then this could result in a memory leak.
                 * Verify that the end of the scatterlist
                 * was cleared prior to us getting here.
                 */
                sgl = &sgl[PAGE_REPORTING_CAPACITY - 1];
                VM_WARN_ON_ONCE(sg_page(sgl));
                return err;
        }

With that we are more-or-less making certain that they called
page_reporting_drain which will zero the scatterlist.


^ permalink raw reply	[flat|nested] 29+ messages in thread

* Re: [PATCH v17 4/9] mm: Introduce Reported pages
  2020-02-21 19:25         ` Alexander Duyck
@ 2020-02-21 20:19           ` Mel Gorman
  0 siblings, 0 replies; 29+ messages in thread
From: Mel Gorman @ 2020-02-21 20:19 UTC (permalink / raw)
  To: Alexander Duyck
  Cc: Alexander Duyck, kvm, david, mst, linux-kernel, linux-mm, akpm,
	yang.zhang.wz, pagupta, konrad.wilk, nitesh, riel, willy,
	lcapitulino, dave.hansen, wei.w.wang, aarcange, pbonzini,
	dan.j.williams, mhocko, vbabka, osalvador

On Fri, Feb 21, 2020 at 11:25:49AM -0800, Alexander Duyck wrote:
> On Thu, 2020-02-20 at 22:35 +0000, Mel Gorman wrote:
> > On Thu, Feb 20, 2020 at 10:44:21AM -0800, Alexander Duyck wrote:
> > > > > +static int
> > > > > +page_reporting_cycle(struct page_reporting_dev_info *prdev, struct zone *zone,
> > > > > +		     unsigned int order, unsigned int mt,
> > > > > +		     struct scatterlist *sgl, unsigned int *offset)
> > > > > +{
> > > > > +	struct free_area *area = &zone->free_area[order];
> > > > > +	struct list_head *list = &area->free_list[mt];
> > > > > +	unsigned int page_len = PAGE_SIZE << order;
> > > > > +	struct page *page, *next;
> > > > > +	int err = 0;
> > > > > +
> > > > > +	/*
> > > > > +	 * Perform early check, if free area is empty there is
> > > > > +	 * nothing to process so we can skip this free_list.
> > > > > +	 */
> > > > > +	if (list_empty(list))
> > > > > +		return err;
> > > > > +
> > > > > +	spin_lock_irq(&zone->lock);
> > > > > +
> > > > > +	/* loop through free list adding unreported pages to sg list */
> > > > > +	list_for_each_entry_safe(page, next, list, lru) {
> > > > > +		/* We are going to skip over the reported pages. */
> > > > > +		if (PageReported(page))
> > > > > +			continue;
> > > > > +
> > > > > +		/* Attempt to pull page from list */
> > > > > +		if (!__isolate_free_page(page, order))
> > > > > +			break;
> > > > > +
> > > > 
> > > > Might want to note that you are breaking because the only reason to fail
> > > > the isolation is that watermarks are not met and we are likely under
> > > > memory pressure. It's not a big issue.
> > > > 
> > > > However, while I think this is correct, it's hard to follow. This loop can
> > > > be broken out of with pages still on the scatter gather list. The current
> > > > flow guarantees that err will not be set at this point so the caller
> > > > cleans it up so we always drain the list either here or in the caller.
> > > 
> > > I can probably submit a follow-up patch to update the comments. The reason
> > > for not returning an error is because I didn't consider it an error that
> > > we encountered the watermark and were not able to pull any more pages.
> > > Instead I considered that the "stop" point for this pass and have it just
> > > exit out of the loop and flush the data.
> > > 
> > 
> > I don't consider it an error and I don't think you should return an
> > error. The comment just needs to explain that the draining happens in
> > the caller in this case. That should be enough of a warning to a future
> > developer to double check the flow after any changes to make sure the
> > drain is reached.
> 
> The comment I can do, that shouldn't be an issue. The point I was getting
> at is that a separate drain call is expected for this any time the
> function is not returning an error, and the only way it can return an
> error is if there was a reporting issue.
> 

I'm not suggesting you return an error. I'm suggesting you put a warn in
before you break due to watermarks *if* there is an error. It should
*never* trigger unless someone modifies the flow and breaks it in which
case the warning will not kill the system but give a strong hint to the
developer that they need to think a bit more.

It's ok to leave it out because at this point, it's a distraction and I
do not see a problem with the current code.

-- 
Mel Gorman
SUSE Labs

^ permalink raw reply	[flat|nested] 29+ messages in thread

end of thread, other threads:[~2020-02-21 20:19 UTC | newest]

Thread overview: 29+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-02-11 22:45 [PATCH v17 0/9] mm / virtio: Provide support for free page reporting Alexander Duyck
2020-02-11 22:46 ` [PATCH v17 1/9] mm: Adjust shuffle code to allow for future coalescing Alexander Duyck
2020-02-11 22:46 ` [PATCH v17 2/9] mm: Use zone and order instead of free area in free_list manipulators Alexander Duyck
2020-02-11 22:46 ` [PATCH v17 3/9] mm: Add function __putback_isolated_page Alexander Duyck
2020-02-19 14:33   ` Mel Gorman
2020-02-11 22:46 ` [PATCH v17 4/9] mm: Introduce Reported pages Alexander Duyck
2020-02-19 14:55   ` Mel Gorman
2020-02-20 18:44     ` Alexander Duyck
2020-02-20 22:35       ` Mel Gorman
2020-02-21 19:25         ` Alexander Duyck
2020-02-21 20:19           ` Mel Gorman
2020-02-11 22:46 ` [PATCH v17 5/9] virtio-balloon: Pull page poisoning config out of free page hinting Alexander Duyck
2020-02-11 22:46 ` [PATCH v17 6/9] virtio-balloon: Add support for providing free page reports to host Alexander Duyck
2020-02-11 22:47 ` [PATCH v17 7/9] mm/page_reporting: Rotate reported pages to the tail of the list Alexander Duyck
2020-02-19 14:59   ` Mel Gorman
2020-02-11 22:47 ` [PATCH v17 8/9] mm/page_reporting: Add budget limit on how many pages can be reported per pass Alexander Duyck
2020-02-19 15:02   ` Mel Gorman
2020-02-11 22:47 ` [PATCH v17 9/9] mm/page_reporting: Add free page reporting documentation Alexander Duyck
2020-02-11 22:51 ` [PATCH v17 QEMU 1/3] virtio-ballon: Implement support for page poison tracking feature Alexander Duyck
2020-02-11 22:51 ` [PATCH v17 QEMU 2/3] virtio-balloon: Add support for providing free page reports to host Alexander Duyck
2020-02-11 22:51 ` [PATCH v17 QEMU 3/3] virtio-balloon: Provide a interface for free page reporting Alexander Duyck
2020-02-11 22:53 ` [PATCH v17 QEMU 4/3 RFC] memory: Add support for MADV_FREE as mechanism to lazy discard pages Alexander Duyck
2020-02-11 23:05 ` [PATCH v17 0/9] mm / virtio: Provide support for free page reporting Andrew Morton
2020-02-11 23:55   ` Alexander Duyck
2020-02-12  0:19     ` Andrew Morton
2020-02-12  1:19       ` Alexander Duyck
2020-02-18 16:37       ` Alexander Duyck
2020-02-19  8:49         ` Mel Gorman
2020-02-19 15:06         ` Mel Gorman

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