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* [PATCH v6 0/6] mm / virtio: Provide support for unused page reporting
@ 2019-08-21 14:59 Alexander Duyck
  2019-08-21 14:59 ` [PATCH v6 1/6] mm: Adjust shuffle code to allow for future coalescing Alexander Duyck
                   ` (9 more replies)
  0 siblings, 10 replies; 16+ messages in thread
From: Alexander Duyck @ 2019-08-21 14:59 UTC (permalink / raw)
  To: nitesh, kvm, mst, david, dave.hansen, linux-kernel, willy,
	mhocko, linux-mm, akpm, virtio-dev, osalvador
  Cc: yang.zhang.wz, pagupta, riel, konrad.wilk, lcapitulino,
	wei.w.wang, aarcange, pbonzini, dan.j.williams,
	alexander.h.duyck

This series provides an asynchronous means of reporting to a hypervisor
that a guest page is no longer in use and can have the data associated
with it dropped. To do this I have implemented functionality that allows
for what I am referring to as unused page reporting

The functionality for this is fairly simple. When enabled it will allocate
statistics to track the number of reported pages in a given free area.
When the number of free pages exceeds this value plus a high water value,
currently 32, it will begin performing page reporting which consists of
pulling pages off of free list and placing them into a scatter list. The
scatterlist is then given to the page reporting device and it will perform
the required action to make the pages "reported", in the case of
virtio-balloon this results in the pages being madvised as MADV_DONTNEED
and as such they are forced out of the guest. After this they are placed
back on the free list, and an additional bit is added if they are not
merged indicating that they are a reported buddy page instead of a
standard buddy page. The cycle then repeats with additional non-reported
pages being pulled until the free areas all consist of reported pages.

I am leaving a number of things hard-coded such as limiting the lowest
order processed to PAGEBLOCK_ORDER, and have left it up to the guest to
determine what the limit is on how many pages it wants to allocate to
process the hints. The upper limit for this is based on the size of the
queue used to store the scattergather list.

My primary testing has just been to verify the memory is being freed after
allocation by running memhog 40g on a 40g guest and watching the total
free memory via /proc/meminfo on the host. With this I have verified most
of the memory is freed after each iteration. As far as performance I have
been mainly focusing on the will-it-scale/page_fault1 test running with
16 vcpus. I have modified it to use Transparent Huge Pages. With this I
see almost no difference, -0.08%, with the patches applied and the feature
disabled. I see a regression of -0.86% with the feature enabled, but the
madvise disabled in the hypervisor due to a device being assigned. With
the feature fully enabled I see a regression of -3.27% versus the baseline
without these patches applied. In my testing I found that most of the
overhead was due to the page zeroing that comes as a result of the pages
having to be faulted back into the guest.

One side effect of these patches is that the guest becomes much more
resilient in terms of NUMA locality. With the pages being freed and then
reallocated when used it allows for the pages to be much closer to the
active thread, and as a result there can be situations where this patch
set will out-perform the stock kernel when the guest memory is not local
to the guest vCPUs. To avoid that in my testing I set the affinity of all
the vCPUs and QEMU instance to the same node.

Changes from the RFC:
https://lore.kernel.org/lkml/20190530215223.13974.22445.stgit@localhost.localdomain/
Moved aeration requested flag out of aerator and into zone->flags.
Moved boundary out of free_area and into local variables for aeration.
Moved aeration cycle out of interrupt and into workqueue.
Left nr_free as total pages instead of splitting it between raw and aerated.
Combined size and physical address values in virtio ring into one 64b value.

Changes from v1:
https://lore.kernel.org/lkml/20190619222922.1231.27432.stgit@localhost.localdomain/
Dropped "waste page treatment" in favor of "page hinting"
Renamed files and functions from "aeration" to "page_hinting"
Moved from page->lru list to scatterlist
Replaced wait on refcnt in shutdown with RCU and cancel_delayed_work_sync
Virtio now uses scatterlist directly instead of intermediate array
Moved stats out of free_area, now in separate area and pointed to from zone
Merged patch 5 into patch 4 to improve review-ability
Updated various code comments throughout

Changes from v2:
https://lore.kernel.org/lkml/20190724165158.6685.87228.stgit@localhost.localdomain/
Dropped "page hinting" in favor of "page reporting"
Renamed files from "hinting" to "reporting"
Replaced "Hinted" page type with "Reported" page flag
Added support for page poisoning while hinting is active
Add QEMU patch that implements PAGE_POISON feature

Changes from v3:
https://lore.kernel.org/lkml/20190801222158.22190.96964.stgit@localhost.localdomain/
Added mutex lock around page reporting startup and shutdown
Fixed reference to "page aeration" in patch 2
Split page reporting function bit out into separate QEMU patch
Limited capacity of scatterlist to vq size - 1 instead of vq size
Added exception handling for case of virtio descriptor allocation failure

Changes from v4:
https://lore.kernel.org/lkml/20190807224037.6891.53512.stgit@localhost.localdomain/
Replaced spin_(un)lock with spin_(un)lock_irq in page_reporting_cycle()
Dropped if/continue for ternary operator in page_reporting_process()
Added checks for isolate and cma types to for_each_reporting_migratetype_order
Added virtio-dev, Michal Hocko, and Oscar Salvador to to:/cc:
Rebased on latest linux-next and QEMU git trees

Changes from v5:
https://lore.kernel.org/lkml/20190812213158.22097.30576.stgit@localhost.localdomain/
Replaced spin_(un)lock with spin_(un)lock_irq in page_reporting_startup()
Updated shuffle code to use "shuffle_pick_tail" and updated patch description
Dropped storage of order and migratettype while page is being reported
Used get_pfnblock_migratetype to determine migratetype of page
Renamed put_reported_page to free_reported_page, added order as argument
Dropped check for CMA type as I believe we should be reporting those
Added code to allow moving of reported pages into and out of isolation
Defined page reporting order as minimum of Huge Page size vs MAX_ORDER - 1
Cleaned up use of static branch usage for page_reporting_notify_enabled

---

Alexander Duyck (6):
      mm: Adjust shuffle code to allow for future coalescing
      mm: Move set/get_pcppage_migratetype to mmzone.h
      mm: Use zone and order instead of free area in free_list manipulators
      mm: Introduce Reported pages
      virtio-balloon: Pull page poisoning config out of free page hinting
      virtio-balloon: Add support for providing unused page reports to host


 drivers/virtio/Kconfig              |    1 
 drivers/virtio/virtio_balloon.c     |   84 ++++++++-
 include/linux/mmzone.h              |  124 ++++++++-----
 include/linux/page-flags.h          |   11 +
 include/linux/page_reporting.h      |  177 ++++++++++++++++++
 include/uapi/linux/virtio_balloon.h |    1 
 mm/Kconfig                          |    5 +
 mm/Makefile                         |    1 
 mm/internal.h                       |   18 ++
 mm/memory_hotplug.c                 |    1 
 mm/page_alloc.c                     |  216 ++++++++++++++++-------
 mm/page_reporting.c                 |  336 +++++++++++++++++++++++++++++++++++
 mm/shuffle.c                        |   40 +++-
 mm/shuffle.h                        |   12 +
 14 files changed, 896 insertions(+), 131 deletions(-)
 create mode 100644 include/linux/page_reporting.h
 create mode 100644 mm/page_reporting.c

--

^ permalink raw reply	[flat|nested] 16+ messages in thread

* [PATCH v6 1/6] mm: Adjust shuffle code to allow for future coalescing
  2019-08-21 14:59 [PATCH v6 0/6] mm / virtio: Provide support for unused page reporting Alexander Duyck
@ 2019-08-21 14:59 ` Alexander Duyck
  2019-08-21 14:59 ` [PATCH v6 2/6] mm: Move set/get_pcppage_migratetype to mmzone.h Alexander Duyck
                   ` (8 subsequent siblings)
  9 siblings, 0 replies; 16+ messages in thread
From: Alexander Duyck @ 2019-08-21 14:59 UTC (permalink / raw)
  To: nitesh, kvm, mst, david, dave.hansen, linux-kernel, willy,
	mhocko, linux-mm, akpm, virtio-dev, osalvador
  Cc: yang.zhang.wz, pagupta, riel, konrad.wilk, lcapitulino,
	wei.w.wang, aarcange, pbonzini, dan.j.williams,
	alexander.h.duyck

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.

While changing out the code I also opted to go for a bit more thread safe
approach to getting the boolean value. This way we can avoid possible cache
line bouncing of the batched entropy between CPUs.

Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
---
 include/linux/mmzone.h |   12 --------
 mm/page_alloc.c        |   70 +++++++++++++++++++++++++++---------------------
 mm/shuffle.c           |   40 ++++++++++++++++-----------
 mm/shuffle.h           |   12 ++++++++
 4 files changed, 75 insertions(+), 59 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 8b5f758942a2..62bfb5a280ce 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 5b799e11fba3..3f8d5afe61fa 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -878,6 +878,36 @@ 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
@@ -906,11 +936,12 @@ 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;
 
 	max_order = min_t(unsigned int, MAX_ORDER, pageblock_order + 1);
 
@@ -979,35 +1010,12 @@ 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;
-		}
-	}
-
-	if (is_shuffle_order(order))
-		add_to_free_area_random(page, &zone->free_area[order],
-				migratetype);
+	area = &zone->free_area[order];
+	if (is_shuffle_order(order) ? shuffle_pick_tail() :
+	    buddy_merge_likely(pfn, buddy_pfn, page, order))
+		add_to_free_area_tail(page, area, migratetype);
 	else
-		add_to_free_area(page, &zone->free_area[order], migratetype);
-
+		add_to_free_area(page, area, migratetype);
 }
 
 /*
diff --git a/mm/shuffle.c b/mm/shuffle.c
index 3ce12481b1dc..345cb4347455 100644
--- a/mm/shuffle.c
+++ b/mm/shuffle.c
@@ -4,7 +4,6 @@
 #include <linux/mm.h>
 #include <linux/init.h>
 #include <linux/mmzone.h>
-#include <linux/random.h>
 #include <linux/moduleparam.h>
 #include "internal.h"
 #include "shuffle.h"
@@ -183,25 +182,34 @@ 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)
+struct batched_bit_entropy {
+	unsigned long entropy_bool;
+	int position;
+};
+
+static DEFINE_PER_CPU(struct batched_bit_entropy, batched_entropy_bool);
+
+bool __shuffle_pick_tail(void)
 {
-	static u64 rand;
-	static u8 rand_bits;
+	struct batched_bit_entropy *batch;
+	unsigned long entropy;
+	int position;
 
 	/*
-	 * The lack of locking is deliberate. If 2 threads race to
-	 * update the rand state it just adds to the entropy.
+	 * We shouldn't need to disable IRQs as the only caller is
+	 * __free_one_page and it should only be called with the zone lock
+	 * held and either from IRQ context or with local IRQs disabled.
 	 */
-	if (rand_bits == 0) {
-		rand_bits = 64;
-		rand = get_random_u64();
+	batch = raw_cpu_ptr(&batched_entropy_bool);
+	position = batch->position;
+
+	if (--position < 0) {
+		batch->entropy_bool = get_random_long();
+		position = BITS_PER_LONG - 1;
 	}
 
-	if (rand & 1)
-		add_to_free_area(page, area, migratetype);
-	else
-		add_to_free_area_tail(page, area, migratetype);
-	rand_bits--;
-	rand >>= 1;
+	batch->position = position;
+	entropy = batch->entropy_bool;
+
+	return 1ul & (entropy >> position);
 }
diff --git a/mm/shuffle.h b/mm/shuffle.h
index 777a257a0d2f..0723eb97f22f 100644
--- a/mm/shuffle.h
+++ b/mm/shuffle.h
@@ -3,6 +3,7 @@
 #ifndef _MM_SHUFFLE_H
 #define _MM_SHUFFLE_H
 #include <linux/jump_label.h>
+#include <linux/random.h>
 
 /*
  * SHUFFLE_ENABLE is called from the command line enabling path, or by
@@ -22,6 +23,7 @@ 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))
@@ -43,6 +45,11 @@ static inline bool is_shuffle_order(int order)
 		return false;
 	return order >= SHUFFLE_ORDER;
 }
+
+static inline bool shuffle_pick_tail(void)
+{
+	return __shuffle_pick_tail();
+}
 #else
 static inline void shuffle_free_memory(pg_data_t *pgdat)
 {
@@ -60,5 +67,10 @@ static inline bool is_shuffle_order(int order)
 {
 	return false;
 }
+
+static inline bool shuffle_pick_tail(void)
+{
+	return false;
+}
 #endif
 #endif /* _MM_SHUFFLE_H */


^ permalink raw reply	[flat|nested] 16+ messages in thread

* [PATCH v6 2/6] mm: Move set/get_pcppage_migratetype to mmzone.h
  2019-08-21 14:59 [PATCH v6 0/6] mm / virtio: Provide support for unused page reporting Alexander Duyck
  2019-08-21 14:59 ` [PATCH v6 1/6] mm: Adjust shuffle code to allow for future coalescing Alexander Duyck
@ 2019-08-21 14:59 ` Alexander Duyck
  2019-08-21 14:59 ` [PATCH v6 3/6] mm: Use zone and order instead of free area in free_list manipulators Alexander Duyck
                   ` (7 subsequent siblings)
  9 siblings, 0 replies; 16+ messages in thread
From: Alexander Duyck @ 2019-08-21 14:59 UTC (permalink / raw)
  To: nitesh, kvm, mst, david, dave.hansen, linux-kernel, willy,
	mhocko, linux-mm, akpm, virtio-dev, osalvador
  Cc: yang.zhang.wz, pagupta, riel, konrad.wilk, lcapitulino,
	wei.w.wang, aarcange, pbonzini, dan.j.williams,
	alexander.h.duyck

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

In order to support page reporting it will be necessary to store and
retrieve the migratetype of a page. To enable that I am moving the set and
get operations for pcppage_migratetype into the mm/internal.h header so
that they can be used outside of the page_alloc.c file.

Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
---
 mm/internal.h   |   18 ++++++++++++++++++
 mm/page_alloc.c |   18 ------------------
 2 files changed, 18 insertions(+), 18 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index 0d5f720c75ab..e4a1a57bbd40 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -549,6 +549,24 @@ static inline bool is_migrate_highatomic_page(struct page *page)
 	return get_pageblock_migratetype(page) == MIGRATE_HIGHATOMIC;
 }
 
+/*
+ * A cached value of the page's pageblock's migratetype, used when the page is
+ * put on a pcplist. Used to avoid the pageblock migratetype lookup when
+ * freeing from pcplists in most cases, at the cost of possibly becoming stale.
+ * Also the migratetype set in the page does not necessarily match the pcplist
+ * index, e.g. page might have MIGRATE_CMA set but be on a pcplist with any
+ * other index - this ensures that it will be put on the correct CMA freelist.
+ */
+static inline int get_pcppage_migratetype(struct page *page)
+{
+	return page->index;
+}
+
+static inline void set_pcppage_migratetype(struct page *page, int migratetype)
+{
+	page->index = migratetype;
+}
+
 void setup_zone_pageset(struct zone *zone);
 extern struct page *alloc_new_node_page(struct page *page, unsigned long node);
 #endif	/* __MM_INTERNAL_H */
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3f8d5afe61fa..c1f9a80b3f28 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -185,24 +185,6 @@ static int __init early_init_on_free(char *buf)
 }
 early_param("init_on_free", early_init_on_free);
 
-/*
- * A cached value of the page's pageblock's migratetype, used when the page is
- * put on a pcplist. Used to avoid the pageblock migratetype lookup when
- * freeing from pcplists in most cases, at the cost of possibly becoming stale.
- * Also the migratetype set in the page does not necessarily match the pcplist
- * index, e.g. page might have MIGRATE_CMA set but be on a pcplist with any
- * other index - this ensures that it will be put on the correct CMA freelist.
- */
-static inline int get_pcppage_migratetype(struct page *page)
-{
-	return page->index;
-}
-
-static inline void set_pcppage_migratetype(struct page *page, int migratetype)
-{
-	page->index = migratetype;
-}
-
 #ifdef CONFIG_PM_SLEEP
 /*
  * The following functions are used by the suspend/hibernate code to temporarily


^ permalink raw reply	[flat|nested] 16+ messages in thread

* [PATCH v6 3/6] mm: Use zone and order instead of free area in free_list manipulators
  2019-08-21 14:59 [PATCH v6 0/6] mm / virtio: Provide support for unused page reporting Alexander Duyck
  2019-08-21 14:59 ` [PATCH v6 1/6] mm: Adjust shuffle code to allow for future coalescing Alexander Duyck
  2019-08-21 14:59 ` [PATCH v6 2/6] mm: Move set/get_pcppage_migratetype to mmzone.h Alexander Duyck
@ 2019-08-21 14:59 ` Alexander Duyck
  2019-08-21 14:59 ` [PATCH v6 4/6] mm: Introduce Reported pages Alexander Duyck
                   ` (6 subsequent siblings)
  9 siblings, 0 replies; 16+ messages in thread
From: Alexander Duyck @ 2019-08-21 14:59 UTC (permalink / raw)
  To: nitesh, kvm, mst, david, dave.hansen, linux-kernel, willy,
	mhocko, linux-mm, akpm, virtio-dev, osalvador
  Cc: yang.zhang.wz, pagupta, riel, konrad.wilk, lcapitulino,
	wei.w.wang, aarcange, pbonzini, dan.j.williams,
	alexander.h.duyck

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.

Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
---
 include/linux/mmzone.h |   70 ++++++++++++++++++++++++++----------------------
 mm/page_alloc.c        |   30 ++++++++-------------
 2 files changed, 49 insertions(+), 51 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 62bfb5a280ce..73b541cbeaae 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]);
@@ -795,6 +763,44 @@ static inline bool pgdat_is_empty(pg_data_t *pgdat)
 	return !pgdat->node_start_pfn && !pgdat->node_spanned_pages;
 }
 
+/* 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--;
+}
+
 #include <linux/memory_hotplug.h>
 
 void build_all_zonelists(pg_data_t *pgdat);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c1f9a80b3f28..fd01031f733d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -921,7 +921,6 @@ 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;
 
@@ -958,7 +957,7 @@ 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;
@@ -992,12 +991,11 @@ 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) ? shuffle_pick_tail() :
 	    buddy_merge_likely(pfn, buddy_pfn, page, order))
-		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);
 }
 
 /*
@@ -2001,13 +1999,11 @@ 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]);
@@ -2021,7 +2017,7 @@ 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);
 	}
 }
@@ -2179,8 +2175,8 @@ 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;
 	}
@@ -2188,7 +2184,6 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
 	return NULL;
 }
 
-
 /*
  * This array describes the order lists are fallen back to when
  * the free lists for the desirable migrate type are depleted
@@ -2254,7 +2249,7 @@ 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;
 	}
@@ -2370,7 +2365,6 @@ 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;
 
@@ -2441,8 +2435,7 @@ 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);
 }
 
 /*
@@ -3113,7 +3106,6 @@ 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;
@@ -3139,7 +3131,7 @@ 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
@@ -8560,7 +8552,7 @@ void zone_pcp_reset(struct zone *zone)
 		pr_info("remove from free list %lx %d %lx\n",
 			pfn, 1 << order, end_pfn);
 #endif
-		del_page_from_free_area(page, &zone->free_area[order]);
+		del_page_from_free_list(page, zone, order);
 		for (i = 0; i < (1 << order); i++)
 			SetPageReserved((page+i));
 		pfn += (1 << order);


^ permalink raw reply	[flat|nested] 16+ messages in thread

* [PATCH v6 4/6] mm: Introduce Reported pages
  2019-08-21 14:59 [PATCH v6 0/6] mm / virtio: Provide support for unused page reporting Alexander Duyck
                   ` (2 preceding siblings ...)
  2019-08-21 14:59 ` [PATCH v6 3/6] mm: Use zone and order instead of free area in free_list manipulators Alexander Duyck
@ 2019-08-21 14:59 ` Alexander Duyck
  2019-08-22 16:18   ` [virtio-dev] " Nitesh Narayan Lal
  2019-08-21 14:59 ` [PATCH v6 5/6] virtio-balloon: Pull page poisoning config out of free page hinting Alexander Duyck
                   ` (5 subsequent siblings)
  9 siblings, 1 reply; 16+ messages in thread
From: Alexander Duyck @ 2019-08-21 14:59 UTC (permalink / raw)
  To: nitesh, kvm, mst, david, dave.hansen, linux-kernel, willy,
	mhocko, linux-mm, akpm, virtio-dev, osalvador
  Cc: yang.zhang.wz, pagupta, riel, konrad.wilk, lcapitulino,
	wei.w.wang, aarcange, pbonzini, dan.j.williams,
	alexander.h.duyck

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.

It adds a set of pointers we shall call "boundary" which represents the
upper boundary between the unreported and reported pages. The general idea
is that in order for a page to cross from one side of the boundary to the
other it will need to go through the reporting process. Ultimately a
free_list has been fully processed when the boundary has been moved from
the tail all they way up to occupying the first entry in the list.

Doing this we should be able to make certain that we keep the reported
pages as one contiguous block in each free list. This will allow us to
efficiently manipulate the free lists whenever we need to go in and start
sending reports to the hypervisor that there are new pages that have been
freed and are no longer in use.

An added advantage to this approach is that we should be reducing the
overall memory footprint of the guest as it will be more likely to recycle
warm pages versus trying to allocate the reported pages that were likely
evicted from the guest memory.

Since we will only be reporting one zone at a time we keep the boundary
limited to being defined for just the zone we are currently reporting pages
from. Doing this we can keep the number of additional pointers needed quite
small. To flag that the boundaries are in place we use a single bit
in the zone to indicate that reporting and the boundaries are active.

The determination of when to start reporting is based on the tracking of
the number of free pages in a given area versus the number of reported
pages in that area. We keep track of the number of reported pages per
free_area in a separate zone specific area. We do this to avoid modifying
the free_area structure as this can lead to false sharing for the highest
order with the zone lock which leads to a noticeable performance
degradation.

Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
---
 include/linux/mmzone.h         |   52 ++++++
 include/linux/page-flags.h     |   11 +
 include/linux/page_reporting.h |  177 +++++++++++++++++++++
 mm/Kconfig                     |    5 +
 mm/Makefile                    |    1 
 mm/memory_hotplug.c            |    1 
 mm/page_alloc.c                |  114 +++++++++++++-
 mm/page_reporting.c            |  336 ++++++++++++++++++++++++++++++++++++++++
 8 files changed, 687 insertions(+), 10 deletions(-)
 create mode 100644 include/linux/page_reporting.h
 create mode 100644 mm/page_reporting.c

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 73b541cbeaae..4a80bb50b226 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -462,6 +462,14 @@ struct zone {
 	seqlock_t		span_seqlock;
 #endif
 
+#ifdef CONFIG_PAGE_REPORTING
+	/*
+	 * Pointer to reported page tracking statistics array. The size of
+	 * the array is MAX_ORDER - PAGE_REPORTING_MIN_ORDER. NULL when
+	 * unused page reporting is not present.
+	 */
+	unsigned long		*reported_pages;
+#endif
 	int initialized;
 
 	/* Write-intensive fields used from the page allocator */
@@ -537,6 +545,14 @@ enum zone_flags {
 	ZONE_BOOSTED_WATERMARK,		/* zone recently boosted watermarks.
 					 * Cleared when kswapd is woken.
 					 */
+	ZONE_PAGE_REPORTING_REQUESTED,	/* zone enabled page reporting and has
+					 * requested flushing the data out of
+					 * higher order pages.
+					 */
+	ZONE_PAGE_REPORTING_ACTIVE,	/* zone enabled page reporting and is
+					 * activly flushing the data out of
+					 * higher order pages.
+					 */
 };
 
 static inline unsigned long zone_managed_pages(struct zone *zone)
@@ -763,6 +779,8 @@ static inline bool pgdat_is_empty(pg_data_t *pgdat)
 	return !pgdat->node_start_pfn && !pgdat->node_spanned_pages;
 }
 
+#include <linux/page_reporting.h>
+
 /* 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)
@@ -777,24 +795,48 @@ static inline void add_to_free_list(struct page *page, struct zone *zone,
 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];
+	struct list_head *tail = get_unreported_tail(zone, order, migratetype);
 
-	list_add_tail(&page->lru, &area->free_list[migratetype]);
-	area->nr_free++;
+	/*
+	 * To prevent the unreported pages from being interleaved with the
+	 * reported ones while we are actively processing pages we will use
+	 * the head of the reported pages to determine the tail of the free
+	 * list.
+	 */
+	list_add_tail(&page->lru, tail);
+	zone->free_area[order].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];
+	struct list_head *tail = get_unreported_tail(zone, order, migratetype);
+
+	/*
+	 * We must get the tail for our target list before moving the page on
+	 * the reported list as we will possibly be replacing the tail page of
+	 * the list with our current page if it is reported.
+	 */
+	if (unlikely(PageReported(page)))
+		move_page_to_reported_list(page, zone, migratetype);
 
-	list_move(&page->lru, &area->free_list[migratetype]);
+	/*
+	 * To prevent unreported pages from being mixed with the reported
+	 * ones we add pages to the tail of the list. By doing this the function
+	 * above can either label them as included in the reported list or not
+	 * and the result will be consistent.
+	 */
+	list_move_tail(&page->lru, tail);
 }
 
 static inline void del_page_from_free_list(struct page *page, struct zone *zone,
 					   unsigned int order)
 {
+	/* remove page from reported list, and clear reported state */
+	if (unlikely(PageReported(page)))
+		del_page_from_reported_list(page, zone);
+
 	list_del(&page->lru);
 	__ClearPageBuddy(page);
 	set_page_private(page, 0);
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index f91cb8898ff0..759a3b3956f2 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,
+
+	/* Buddy pages. Used to track which pages have been 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..5d434a7f8e16
--- /dev/null
+++ b/include/linux/page_reporting.h
@@ -0,0 +1,177 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_PAGE_REPORTING_H
+#define _LINUX_PAGE_REPORTING_H
+
+#include <linux/mmzone.h>
+#include <linux/jump_label.h>
+#include <linux/pageblock-flags.h>
+
+#if defined(CONFIG_HUGETLB_PAGE) && HUGETLB_PAGE_ORDER < MAX_ORDER
+#define PAGE_REPORTING_MIN_ORDER	HUGETLB_PAGE_ORDER
+#else
+#define PAGE_REPORTING_MIN_ORDER	(MAX_ORDER - 1)
+#endif
+#define PAGE_REPORTING_HWM		32
+
+#ifdef CONFIG_PAGE_REPORTING
+struct page_reporting_dev_info {
+	/* function that alters pages to make them "reported" */
+	void (*report)(struct page_reporting_dev_info *phdev,
+		       unsigned int nents);
+
+	/* scatterlist containing pages to be processed */
+	struct scatterlist *sg;
+
+	/*
+	 * Upper limit on the number of pages that the react function
+	 * expects to be placed into the batch list to be processed.
+	 */
+	unsigned long capacity;
+
+	/* work struct for processing reports */
+	struct delayed_work work;
+
+	/*
+	 * The number of zones requesting reporting, plus one additional if
+	 * processing thread is active.
+	 */
+	atomic_t refcnt;
+};
+
+/* Boundary functions */
+struct list_head *__page_reporting_get_boundary(unsigned int order,
+						int migratetype);
+void page_reporting_del_from_boundary(struct page *page, struct zone *zone);
+void page_reporting_add_to_boundary(struct page *page, struct zone *zone,
+				    int migratetype);
+void page_reporting_move_to_boundary(struct page *page, struct zone *zone,
+				     int migratetype);
+
+/* Reported page accessors, defined in page_alloc.c */
+struct page *get_unreported_page(struct zone *zone, unsigned int order,
+				 int migratetype);
+void free_reported_page(struct page *page, unsigned int order);
+
+/* Tear-down and bring-up for page reporting devices */
+void page_reporting_shutdown(struct page_reporting_dev_info *phdev);
+int page_reporting_startup(struct page_reporting_dev_info *phdev);
+
+void __page_reporting_free_stats(struct zone *zone);
+void __page_reporting_request(struct zone *zone);
+#endif /* CONFIG_PAGE_REPORTING */
+
+/*
+ * Method for obtaining the tail of the free list. Using this allows for
+ * tail insertions of unreported pages into the region that is currently
+ * being scanned so as to avoid interleaving reported and unreported pages.
+ */
+static inline struct list_head *
+get_unreported_tail(struct zone *zone, unsigned int order, int migratetype)
+{
+#ifdef CONFIG_PAGE_REPORTING
+	if (order >= PAGE_REPORTING_MIN_ORDER &&
+	    test_bit(ZONE_PAGE_REPORTING_ACTIVE, &zone->flags))
+		return __page_reporting_get_boundary(order, migratetype);
+#endif
+	return &zone->free_area[order].free_list[migratetype];
+}
+
+/*
+ * Functions for adding/removing pages from reported end of list.
+ * All of them expect the zone lock to be held to maintain
+ * consistency of the reported list as a subset of the free list.
+ */
+static inline void add_page_to_reported_list(struct page *page,
+					     struct zone *zone,
+					     int order,
+					     int migratetype)
+{
+#ifdef CONFIG_PAGE_REPORTING
+	/* flag page as reported */
+	__SetPageReported(page);
+
+	/* update areated page accounting */
+	zone->reported_pages[order - PAGE_REPORTING_MIN_ORDER]++;
+
+	/* update boundary of new migratetype and record it */
+	page_reporting_add_to_boundary(page, zone, migratetype);
+#endif
+}
+
+static inline void del_page_from_reported_list(struct page *page,
+					       struct zone *zone)
+{
+#ifdef CONFIG_PAGE_REPORTING
+	/* push boundary back if we removed the upper boundary */
+	if (test_bit(ZONE_PAGE_REPORTING_ACTIVE, &zone->flags))
+		page_reporting_del_from_boundary(page, zone);
+
+	/* page_private will contain the page order, so just use it directly */
+	zone->reported_pages[page_private(page) - PAGE_REPORTING_MIN_ORDER]--;
+
+	/* clear the flag so we can report on it when it returns */
+	__ClearPageReported(page);
+#endif
+}
+
+static inline void move_page_to_reported_list(struct page *page,
+					      struct zone *zone,
+					      int migratetype)
+{
+#ifdef CONFIG_PAGE_REPORTING
+	page_reporting_move_to_boundary(page, zone, migratetype);
+#endif
+}
+
+/* Free reported_pages and reset reported page tracking count to 0 */
+static inline void page_reporting_reset(struct zone *zone)
+{
+#ifdef CONFIG_PAGE_REPORTING
+	if (zone->reported_pages)
+		__page_reporting_free_stats(zone);
+#endif
+}
+
+DECLARE_STATIC_KEY_FALSE(page_reporting_notify_enabled);
+
+/**
+ * page_reporting_notify_free - Free page notification to start page processing
+ * @zone: Pointer to current zone of last page processed
+ * @order: Order of last page added to zone
+ *
+ * This function is meant to act as a screener for __page_reporting_request
+ * 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(struct zone *zone, int order)
+{
+#ifdef CONFIG_PAGE_REPORTING
+	unsigned long nr_reported;
+
+	/* Called from hot path in __free_one_page() */
+	if (!static_branch_unlikely(&page_reporting_notify_enabled))
+		return;
+
+	/* Limit notifications only to higher order pages */
+	if (order < PAGE_REPORTING_MIN_ORDER)
+		return;
+
+	/* Do not bother with tests if we have already requested reporting */
+	if (test_bit(ZONE_PAGE_REPORTING_REQUESTED, &zone->flags))
+		return;
+
+	/* If reported_pages is not populated, assume 0 */
+	nr_reported = zone->reported_pages ?
+		    zone->reported_pages[order - PAGE_REPORTING_MIN_ORDER] : 0;
+
+	/* Only request it if we have enough to begin the page reporting */
+	if (zone->free_area[order].nr_free < nr_reported + PAGE_REPORTING_HWM)
+		return;
+
+	/* This is slow, but should be called very rarely */
+	__page_reporting_request(zone);
+#endif
+}
+#endif /*_LINUX_PAGE_REPORTING_H */
diff --git a/mm/Kconfig b/mm/Kconfig
index a5dae9a7eb51..be1a5db50df5 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -237,6 +237,11 @@ config COMPACTION
           linux-mm@kvack.org.
 
 #
+# support for unused page reporting
+config PAGE_REPORTING
+	bool
+
+#
 # support for page migration
 #
 config MIGRATION
diff --git a/mm/Makefile b/mm/Makefile
index d11de59e9c3c..4dcf09cd8280 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -104,3 +104,4 @@ obj-$(CONFIG_PERCPU_STATS) += percpu-stats.o
 obj-$(CONFIG_ZONE_DEVICE) += memremap.o
 obj-$(CONFIG_HMM_MIRROR) += hmm.o
 obj-$(CONFIG_MEMFD_CREATE) += memfd.o
+obj-$(CONFIG_PAGE_REPORTING) += page_reporting.o
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 32a5386758ce..d0b813567ff4 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1614,6 +1614,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
 	if (!populated_zone(zone)) {
 		zone_pcp_reset(zone);
 		build_all_zonelists(NULL);
+		page_reporting_reset(zone);
 	} else
 		zone_pcp_update(zone);
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index fd01031f733d..d3f19e09a507 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -68,6 +68,7 @@
 #include <linux/lockdep.h>
 #include <linux/nmi.h>
 #include <linux/psi.h>
+#include <linux/page_reporting.h>
 
 #include <asm/sections.h>
 #include <asm/tlbflush.h>
@@ -916,7 +917,7 @@ static inline struct capture_control *task_capc(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 reported)
 {
 	struct capture_control *capc = task_capc(zone);
 	unsigned long uninitialized_var(buddy_pfn);
@@ -991,11 +992,20 @@ static inline void __free_one_page(struct page *page,
 done_merging:
 	set_page_order(page, order);
 
-	if (is_shuffle_order(order) ? shuffle_pick_tail() :
-	    buddy_merge_likely(pfn, buddy_pfn, page, order))
+	if (reported ||
+	    (is_shuffle_order(order) ? shuffle_pick_tail() :
+	     buddy_merge_likely(pfn, buddy_pfn, page, order)))
 		add_to_free_list_tail(page, zone, order, migratetype);
 	else
 		add_to_free_list(page, zone, order, migratetype);
+
+	/*
+	 * No need to notify on a reported page as the total count of
+	 * unreported pages will not have increased since we have essentially
+	 * merged the reported page with one or more unreported pages.
+	 */
+	if (!reported)
+		page_reporting_notify_free(zone, order);
 }
 
 /*
@@ -1306,7 +1316,7 @@ 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, false);
 		trace_mm_page_pcpu_drain(page, 0, mt);
 	}
 	spin_unlock(&zone->lock);
@@ -1322,7 +1332,7 @@ 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, false);
 	spin_unlock(&zone->lock);
 }
 
@@ -2184,6 +2194,100 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
 	return NULL;
 }
 
+#ifdef CONFIG_PAGE_REPORTING
+/**
+ * free_reported_page - Return a now-reported page back where we got it
+ * @page: Page that was reported
+ *
+ * This function will pull the migratetype and order information out
+ * of the page and attempt to return it where it found it. If the page
+ * is added to the free list without changes we will mark it as being
+ * reported.
+ */
+void free_reported_page(struct page *page, unsigned int order)
+{
+	struct zone *zone = page_zone(page);
+	unsigned long pfn;
+	unsigned int mt;
+
+	/* zone lock should be held when this function is called */
+	lockdep_assert_held(&zone->lock);
+
+	pfn = page_to_pfn(page);
+	mt = get_pfnblock_migratetype(page, pfn);
+	__free_one_page(page, pfn, zone, order, mt, true);
+
+	/*
+	 * If page was not comingled with another page we can consider
+	 * the result to be "reported" since part of the page hasn't been
+	 * modified, otherwise we would need to report on the new larger
+	 * page.
+	 */
+	if (PageBuddy(page) && page_order(page) == order)
+		add_page_to_reported_list(page, zone, order, mt);
+}
+
+/**
+ * get_unreported_page - Pull an unreported page from the free_list
+ * @zone: Zone to draw pages from
+ * @order: Order to draw pages from
+ * @mt: Migratetype to draw pages from
+ *
+ * This function will obtain a page from the free list. It will start by
+ * attempting to pull from the tail of the free list and if that is already
+ * reported on it will instead pull the head if that is unreported.
+ *
+ * The page will have the migrate type and order stored in the page
+ * metadata. While being processed the page will not be avaialble for
+ * allocation.
+ *
+ * Return: page pointer if raw page found, otherwise NULL
+ */
+struct page *get_unreported_page(struct zone *zone, unsigned int order, int mt)
+{
+	struct list_head *tail = get_unreported_tail(zone, order, mt);
+	struct free_area *area = &(zone->free_area[order]);
+	struct list_head *list = &area->free_list[mt];
+	struct page *page;
+
+	/* zone lock should be held when this function is called */
+	lockdep_assert_held(&zone->lock);
+
+	/* Find a page of the appropriate size in the preferred list */
+	page = list_last_entry(tail, struct page, lru);
+	list_for_each_entry_from_reverse(page, list, lru) {
+		/* If we entered this loop then the "raw" list isn't empty */
+
+		/* If the page is reported try the head of the list */
+		if (PageReported(page)) {
+			page = list_first_entry(list, struct page, lru);
+
+			/*
+			 * If both the head and tail are reported then reset
+			 * the boundary so that we read as an empty list
+			 * next time and bail out.
+			 */
+			if (PageReported(page)) {
+				page_reporting_add_to_boundary(page, zone, mt);
+				break;
+			}
+		}
+
+		del_page_from_free_list(page, zone, order);
+
+		/*
+		 * Page will not be available for allocation while we are
+		 * processing it so update the freepage state.
+		 */
+		__mod_zone_freepage_state(zone, -(1 << order), mt);
+
+		return page;
+	}
+
+	return NULL;
+}
+#endif /* CONFIG_PAGE_REPORTING */
+
 /*
  * This array describes the order lists are fallen back to when
  * the free lists for the desirable migrate type are depleted
diff --git a/mm/page_reporting.c b/mm/page_reporting.c
new file mode 100644
index 000000000000..b6858592bcfa
--- /dev/null
+++ b/mm/page_reporting.c
@@ -0,0 +1,336 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/mm.h>
+#include <linux/mmzone.h>
+#include <linux/page-isolation.h>
+#include <linux/gfp.h>
+#include <linux/export.h>
+#include <linux/delay.h>
+#include <linux/slab.h>
+#include <linux/scatterlist.h>
+#include "internal.h"
+
+static struct page_reporting_dev_info __rcu *ph_dev_info __read_mostly;
+
+struct list_head *boundary[MAX_ORDER - PAGE_REPORTING_MIN_ORDER][MIGRATE_TYPES];
+
+static void page_reporting_reset_boundary(struct zone *zone, unsigned int order,
+					  unsigned int migratetype)
+{
+	boundary[order - PAGE_REPORTING_MIN_ORDER][migratetype] =
+			&zone->free_area[order].free_list[migratetype];
+}
+
+#define for_each_reporting_migratetype_order(_order, _type) \
+	for (_order = MAX_ORDER; _order-- != PAGE_REPORTING_MIN_ORDER;) \
+		for (_type = MIGRATE_TYPES; _type--;) \
+			if (!is_migrate_isolate(_type))
+
+static int page_reporting_populate_metadata(struct zone *zone)
+{
+	unsigned int order, mt;
+
+	/*
+	 * We need to make sure we have somewhere to store the tracking
+	 * data for how many reported pages are in the zone. To do that
+	 * we need to make certain zone->reported_pages is populated.
+	 */
+	if (!zone->reported_pages) {
+		zone->reported_pages =
+			kcalloc(MAX_ORDER - PAGE_REPORTING_MIN_ORDER,
+				sizeof(unsigned long),
+				GFP_KERNEL);
+		if (!zone->reported_pages)
+			return -ENOMEM;
+	}
+
+	/* Update boundary data to reflect the zone we are currently working */
+	for_each_reporting_migratetype_order(order, mt)
+		page_reporting_reset_boundary(zone, order, mt);
+
+	return 0;
+}
+
+struct list_head *__page_reporting_get_boundary(unsigned int order,
+						int migratetype)
+{
+	return boundary[order - PAGE_REPORTING_MIN_ORDER][migratetype];
+}
+
+void page_reporting_del_from_boundary(struct page *page, struct zone *zone)
+{
+	unsigned int order = page_private(page) - PAGE_REPORTING_MIN_ORDER;
+	int mt = get_pcppage_migratetype(page);
+	struct list_head **tail = &boundary[order][mt];
+
+	if (*tail == &page->lru)
+		*tail = page->lru.next;
+}
+
+void page_reporting_add_to_boundary(struct page *page, struct zone *zone,
+				    int migratetype)
+{
+	unsigned int order = page_private(page) - PAGE_REPORTING_MIN_ORDER;
+
+	boundary[order][migratetype] = &page->lru;
+	set_pcppage_migratetype(page, migratetype);
+}
+
+void page_reporting_move_to_boundary(struct page *page, struct zone *zone,
+				     int dest_mt)
+{
+	unsigned int order = page_private(page) - PAGE_REPORTING_MIN_ORDER;
+
+	/*
+	 * We essentially have two options available to us. The first is to
+	 * move the page from the boundary list on one migratetype to the
+	 * list for the new migratetype assuming reporting is still active.
+	 *
+	 * The other option is to clear the reported state of the page as
+	 * we will not be adding it to the group of pages that were already
+	 * reported. It is cheaper to just rereport such pages then go
+	 * through and do a special search to skip over them.
+	 */
+	if (test_bit(ZONE_PAGE_REPORTING_ACTIVE, &zone->flags)) {
+		int src_mt = get_pcppage_migratetype(page);
+		struct list_head **tail = &boundary[order][src_mt];
+
+		if (*tail == &page->lru)
+			*tail = page->lru.next;
+
+		boundary[order][dest_mt] = &page->lru;
+		set_pcppage_migratetype(page, dest_mt);
+	} else if (!is_migrate_isolate(dest_mt)) {
+		zone->reported_pages[order]--;
+		__ClearPageReported(page);
+	}
+}
+
+static unsigned int page_reporting_fill(struct zone *zone,
+					struct page_reporting_dev_info *phdev)
+{
+	struct scatterlist *sg = phdev->sg;
+	unsigned int order, mt, count = 0;
+
+	sg_init_table(phdev->sg, phdev->capacity);
+
+	for_each_reporting_migratetype_order(order, mt) {
+		struct page *page;
+
+		/*
+		 * Pull pages from free list until we have drained
+		 * it or we have reached capacity.
+		 */
+		while ((page = get_unreported_page(zone, order, mt))) {
+			sg_set_page(&sg[count], page, PAGE_SIZE << order, 0);
+
+			if (++count == phdev->capacity)
+				return count;
+		}
+	}
+
+	/* mark end of scatterlist due to underflow */
+	if (count)
+		sg_mark_end(&sg[count - 1]);
+
+	/*
+	 * If there are no longer enough free pages to fully populate
+	 * the scatterlist, then we can just shut it down for this zone.
+	 */
+	__clear_bit(ZONE_PAGE_REPORTING_REQUESTED, &zone->flags);
+	atomic_dec(&phdev->refcnt);
+
+	return count;
+}
+
+static void page_reporting_drain(struct page_reporting_dev_info *phdev)
+{
+	struct scatterlist *sg = phdev->sg;
+
+	/*
+	 * Drain the now reported pages back into their respective
+	 * free lists/areas. We assume at least one page is populated.
+	 */
+	do {
+		free_reported_page(sg_page(sg), get_order(sg->length));
+	} while (!sg_is_last(sg++));
+}
+
+/*
+ * The page reporting cycle consists of 4 stages, fill, report, drain, and idle.
+ * We will cycle through the first 3 stages until we fail to obtain any
+ * pages, in that case we will switch to idle.
+ */
+static void page_reporting_cycle(struct zone *zone,
+				 struct page_reporting_dev_info *phdev)
+{
+	/*
+	 * Guarantee boundaries and stats are populated before we
+	 * start placing reported pages in the zone.
+	 */
+	if (page_reporting_populate_metadata(zone))
+		return;
+
+	spin_lock_irq(&zone->lock);
+
+	/* set bit indicating boundaries are present */
+	__set_bit(ZONE_PAGE_REPORTING_ACTIVE, &zone->flags);
+
+	do {
+		/* Pull pages out of allocator into a scaterlist */
+		unsigned int nents = page_reporting_fill(zone, phdev);
+
+		/* no pages were acquired, give up */
+		if (!nents)
+			break;
+
+		spin_unlock_irq(&zone->lock);
+
+		/* begin processing pages in local list */
+		phdev->report(phdev, nents);
+
+		spin_lock_irq(&zone->lock);
+
+		/*
+		 * We should have a scatterlist of pages that have been
+		 * processed. Return them to their original free lists.
+		 */
+		page_reporting_drain(phdev);
+
+		/* keep pulling pages till there are none to pull */
+	} while (test_bit(ZONE_PAGE_REPORTING_REQUESTED, &zone->flags));
+
+	/* processing of the zone is complete, we can disable boundaries */
+	__clear_bit(ZONE_PAGE_REPORTING_ACTIVE, &zone->flags);
+
+	spin_unlock_irq(&zone->lock);
+}
+
+static void page_reporting_process(struct work_struct *work)
+{
+	struct delayed_work *d_work = to_delayed_work(work);
+	struct page_reporting_dev_info *phdev =
+		container_of(d_work, struct page_reporting_dev_info, work);
+	struct zone *zone = first_online_pgdat()->node_zones;
+
+	do {
+		if (test_bit(ZONE_PAGE_REPORTING_REQUESTED, &zone->flags))
+			page_reporting_cycle(zone, phdev);
+
+		/* Move to next zone, if at end of list start over */
+		zone = next_zone(zone) ? : first_online_pgdat()->node_zones;
+
+		/*
+		 * As long as refcnt has not reached zero there are still
+		 * zones to be processed.
+		 */
+	} while (atomic_read(&phdev->refcnt));
+}
+
+/* request page reporting on this zone */
+void __page_reporting_request(struct zone *zone)
+{
+	struct page_reporting_dev_info *phdev;
+
+	rcu_read_lock();
+
+	/*
+	 * We use RCU to protect the ph_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.
+	 */
+	phdev = rcu_dereference(ph_dev_info);
+	if (unlikely(!phdev))
+		return;
+
+	/*
+	 * We can use separate test and set operations here as there
+	 * is nothing else that can set or clear this bit while we are
+	 * holding the zone lock. The advantage to doing it this way is
+	 * that we don't have to dirty the cacheline unless we are
+	 * changing the value.
+	 */
+	__set_bit(ZONE_PAGE_REPORTING_REQUESTED, &zone->flags);
+
+	/*
+	 * Delay the start of work to allow a sizable queue to
+	 * build. For now we are limiting this to running no more
+	 * than 10 times per second.
+	 */
+	if (!atomic_fetch_inc(&phdev->refcnt))
+		schedule_delayed_work(&phdev->work, HZ / 10);
+
+	rcu_read_unlock();
+}
+
+void __page_reporting_free_stats(struct zone *zone)
+{
+	/* free reported_page statisitics */
+	kfree(zone->reported_pages);
+	zone->reported_pages = NULL;
+}
+
+static DEFINE_MUTEX(page_reporting_mutex);
+DEFINE_STATIC_KEY_FALSE(page_reporting_notify_enabled);
+
+void page_reporting_shutdown(struct page_reporting_dev_info *phdev)
+{
+	mutex_lock(&page_reporting_mutex);
+
+	if (rcu_access_pointer(ph_dev_info) == phdev) {
+		/* Disable page reporting notification */
+		static_branch_disable(&page_reporting_notify_enabled);
+		RCU_INIT_POINTER(ph_dev_info, NULL);
+		synchronize_rcu();
+
+		/* Flush any existing work, and lock it out */
+		cancel_delayed_work_sync(&phdev->work);
+
+		/* Free scatterlist */
+		kfree(phdev->sg);
+		phdev->sg = NULL;
+	}
+
+	mutex_unlock(&page_reporting_mutex);
+}
+EXPORT_SYMBOL_GPL(page_reporting_shutdown);
+
+int page_reporting_startup(struct page_reporting_dev_info *phdev)
+{
+	struct zone *zone;
+	int err = 0;
+
+	mutex_lock(&page_reporting_mutex);
+
+	/* nothing to do if already in use */
+	if (rcu_access_pointer(ph_dev_info)) {
+		err = -EBUSY;
+		goto err_out;
+	}
+
+	/* allocate scatterlist to store pages being reported on */
+	phdev->sg = kcalloc(phdev->capacity, sizeof(*phdev->sg), GFP_KERNEL);
+	if (!phdev->sg) {
+		err = -ENOMEM;
+		goto err_out;
+	}
+
+	/* initialize refcnt and work structures */
+	atomic_set(&phdev->refcnt, 0);
+	INIT_DELAYED_WORK(&phdev->work, &page_reporting_process);
+
+	/* assign device, and begin initial flush of populated zones */
+	rcu_assign_pointer(ph_dev_info, phdev);
+	for_each_populated_zone(zone) {
+		spin_lock_irq(&zone->lock);
+		__page_reporting_request(zone);
+		spin_unlock_irq(&zone->lock);
+	}
+
+	/* enable page reporting notification */
+	static_branch_enable(&page_reporting_notify_enabled);
+err_out:
+	mutex_unlock(&page_reporting_mutex);
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(page_reporting_startup);


^ permalink raw reply	[flat|nested] 16+ messages in thread

* [PATCH v6 5/6] virtio-balloon: Pull page poisoning config out of free page hinting
  2019-08-21 14:59 [PATCH v6 0/6] mm / virtio: Provide support for unused page reporting Alexander Duyck
                   ` (3 preceding siblings ...)
  2019-08-21 14:59 ` [PATCH v6 4/6] mm: Introduce Reported pages Alexander Duyck
@ 2019-08-21 14:59 ` Alexander Duyck
  2019-08-21 15:00 ` [PATCH v6 6/6] virtio-balloon: Add support for providing unused page reports to host Alexander Duyck
                   ` (4 subsequent siblings)
  9 siblings, 0 replies; 16+ messages in thread
From: Alexander Duyck @ 2019-08-21 14:59 UTC (permalink / raw)
  To: nitesh, kvm, mst, david, dave.hansen, linux-kernel, willy,
	mhocko, linux-mm, akpm, virtio-dev, osalvador
  Cc: yang.zhang.wz, pagupta, riel, konrad.wilk, lcapitulino,
	wei.w.wang, aarcange, pbonzini, dan.j.williams,
	alexander.h.duyck

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 unused page reporting. As such pull it out and make it a
separate bit of config in the probe function.

In addition we can actually wrap the code in a check for NO_SANITY. If we
don't care what is actually in the page we can just default to 0 and leave
it there.

Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
---
 drivers/virtio/virtio_balloon.c |   19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 226fbb995fb0..2c19457ab573 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -842,7 +842,6 @@ 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) {
@@ -909,11 +908,19 @@ 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)) {
-			memset(&poison_val, PAGE_POISON, sizeof(poison_val));
-			virtio_cwrite(vb->vdev, struct virtio_balloon_config,
-				      poison_val, &poison_val);
-		}
+	}
+	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) {
+		__u32 poison_val = 0;
+
+#if !defined(CONFIG_PAGE_POISONING_NO_SANITY)
+		/*
+		 * Let hypervisor know that we are expecting a specific
+		 * value to be written back in unused pages.
+		 */
+		memset(&poison_val, PAGE_POISON, sizeof(poison_val));
+#endif
+		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


^ permalink raw reply	[flat|nested] 16+ messages in thread

* [PATCH v6 6/6] virtio-balloon: Add support for providing unused page reports to host
  2019-08-21 14:59 [PATCH v6 0/6] mm / virtio: Provide support for unused page reporting Alexander Duyck
                   ` (4 preceding siblings ...)
  2019-08-21 14:59 ` [PATCH v6 5/6] virtio-balloon: Pull page poisoning config out of free page hinting Alexander Duyck
@ 2019-08-21 15:00 ` Alexander Duyck
  2019-08-21 15:00 ` [PATCH v6 QEMU 1/3] virtio-ballon: Implement support for page poison tracking feature Alexander Duyck
                   ` (3 subsequent siblings)
  9 siblings, 0 replies; 16+ messages in thread
From: Alexander Duyck @ 2019-08-21 15:00 UTC (permalink / raw)
  To: nitesh, kvm, mst, david, dave.hansen, linux-kernel, willy,
	mhocko, linux-mm, akpm, virtio-dev, osalvador
  Cc: yang.zhang.wz, pagupta, riel, konrad.wilk, lcapitulino,
	wei.w.wang, aarcange, pbonzini, dan.j.williams,
	alexander.h.duyck

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.

Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
---
 drivers/virtio/Kconfig              |    1 +
 drivers/virtio/virtio_balloon.c     |   65 +++++++++++++++++++++++++++++++++++
 include/uapi/linux/virtio_balloon.h |    1 +
 3 files changed, 67 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 2c19457ab573..52f9eeda1877 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
@@ -37,6 +38,9 @@
 #define VIRTIO_BALLOON_FREE_PAGE_SIZE \
 	(1 << (VIRTIO_BALLOON_FREE_PAGE_ORDER + PAGE_SHIFT))
 
+/*  limit on the number of pages that can be on the reporting vq */
+#define VIRTIO_BALLOON_VRING_HINTS_MAX	16
+
 #ifdef CONFIG_BALLOON_COMPACTION
 static struct vfsmount *balloon_mnt;
 #endif
@@ -46,6 +50,7 @@ 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
 };
 
@@ -113,6 +118,10 @@ struct virtio_balloon {
 
 	/* To register a shrinker to shrink memory upon memory pressure */
 	struct shrinker shrinker;
+
+	/* Unused page reporting device */
+	struct virtqueue *reporting_vq;
+	struct page_reporting_dev_info ph_dev_info;
 };
 
 static struct virtio_device_id id_table[] = {
@@ -152,6 +161,32 @@ static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
 
 }
 
+void virtballoon_unused_page_report(struct page_reporting_dev_info *ph_dev_info,
+				    unsigned int nents)
+{
+	struct virtio_balloon *vb =
+		container_of(ph_dev_info, struct virtio_balloon, ph_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, ph_dev_info->sg, nents, vb,
+				  GFP_NOWAIT | __GFP_NOWARN);
+
+	/*
+	 * In the extremely unlikely case that something has changed and we
+	 * are able to trigger an error we will simply display a warning
+	 * and exit without actually processing the pages.
+	 */
+	if (WARN_ON(err))
+		return;
+
+	virtqueue_kick(vq);
+
+	/* When host has read buffer, this completes via balloon_ack */
+	wait_event(vb->acked, virtqueue_get_buf(vq, &unused));
+}
+
 static void set_page_pfns(struct virtio_balloon *vb,
 			  __virtio32 pfns[], struct page *page)
 {
@@ -476,6 +511,7 @@ static int init_vqs(struct virtio_balloon *vb)
 	names[VIRTIO_BALLOON_VQ_DEFLATE] = "deflate";
 	names[VIRTIO_BALLOON_VQ_STATS] = 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";
@@ -487,11 +523,19 @@ 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)
 		return err;
 
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING))
+		vb->reporting_vq = vqs[VIRTIO_BALLOON_VQ_REPORTING];
+
 	vb->inflate_vq = vqs[VIRTIO_BALLOON_VQ_INFLATE];
 	vb->deflate_vq = vqs[VIRTIO_BALLOON_VQ_DEFLATE];
 	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
@@ -931,12 +975,30 @@ static int virtballoon_probe(struct virtio_device *vdev)
 		if (err)
 			goto out_del_balloon_wq;
 	}
+
+	vb->ph_dev_info.report = virtballoon_unused_page_report;
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) {
+		unsigned int capacity;
+
+		capacity = min_t(unsigned int,
+				 virtqueue_get_vring_size(vb->reporting_vq) - 1,
+				 VIRTIO_BALLOON_VRING_HINTS_MAX);
+		vb->ph_dev_info.capacity = capacity;
+
+		err = page_reporting_startup(&vb->ph_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);
@@ -965,6 +1027,8 @@ 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_shutdown(&vb->ph_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);
@@ -1034,6 +1098,7 @@ 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] 16+ messages in thread

* [PATCH v6 QEMU 1/3] virtio-ballon: Implement support for page poison tracking feature
  2019-08-21 14:59 [PATCH v6 0/6] mm / virtio: Provide support for unused page reporting Alexander Duyck
                   ` (5 preceding siblings ...)
  2019-08-21 15:00 ` [PATCH v6 6/6] virtio-balloon: Add support for providing unused page reports to host Alexander Duyck
@ 2019-08-21 15:00 ` Alexander Duyck
  2019-08-21 15:00 ` [PATCH v6 QEMU 2/3] virtio-balloon: Add bit to notify guest of unused page reporting Alexander Duyck
                   ` (2 subsequent siblings)
  9 siblings, 0 replies; 16+ messages in thread
From: Alexander Duyck @ 2019-08-21 15:00 UTC (permalink / raw)
  To: nitesh, kvm, mst, david, dave.hansen, linux-kernel, linux-mm,
	akpm, virtio-dev
  Cc: yang.zhang.wz, pagupta, riel, konrad.wilk, willy, lcapitulino,
	wei.w.wang, aarcange, pbonzini, dan.j.williams, mhocko,
	alexander.h.duyck, 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 25de15430710..003b3ebcfdfb 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -530,6 +530,15 @@ 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;
@@ -617,12 +626,10 @@ 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);
 }
 
@@ -633,6 +640,7 @@ 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 =
@@ -696,6 +704,8 @@ 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);
 }
 
@@ -705,6 +715,9 @@ 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;
 }
@@ -846,6 +859,8 @@ 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)
@@ -908,6 +923,8 @@ 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] 16+ messages in thread

* [PATCH v6 QEMU 2/3] virtio-balloon: Add bit to notify guest of unused page reporting
  2019-08-21 14:59 [PATCH v6 0/6] mm / virtio: Provide support for unused page reporting Alexander Duyck
                   ` (6 preceding siblings ...)
  2019-08-21 15:00 ` [PATCH v6 QEMU 1/3] virtio-ballon: Implement support for page poison tracking feature Alexander Duyck
@ 2019-08-21 15:00 ` Alexander Duyck
  2019-08-21 15:00 ` [PATCH v6 QEMU 3/3] virtio-balloon: Provide a interface for " Alexander Duyck
  2019-08-22 10:43 ` [PATCH v6 0/6] mm / virtio: Provide support " Pankaj Gupta
  9 siblings, 0 replies; 16+ messages in thread
From: Alexander Duyck @ 2019-08-21 15:00 UTC (permalink / raw)
  To: nitesh, kvm, mst, david, dave.hansen, linux-kernel, linux-mm,
	akpm, virtio-dev
  Cc: yang.zhang.wz, pagupta, riel, konrad.wilk, willy, lcapitulino,
	wei.w.wang, aarcange, pbonzini, dan.j.williams, mhocko,
	alexander.h.duyck, osalvador

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

Add a bit for the page reporting feature provided by virtio-balloon.

This patch should be replaced once the feature is added to the Linux kernel
and the bit is backported into this exported kernel header.

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] 16+ messages in thread

* [PATCH v6 QEMU 3/3] virtio-balloon: Provide a interface for unused page reporting
  2019-08-21 14:59 [PATCH v6 0/6] mm / virtio: Provide support for unused page reporting Alexander Duyck
                   ` (7 preceding siblings ...)
  2019-08-21 15:00 ` [PATCH v6 QEMU 2/3] virtio-balloon: Add bit to notify guest of unused page reporting Alexander Duyck
@ 2019-08-21 15:00 ` " Alexander Duyck
  2019-08-22 10:43 ` [PATCH v6 0/6] mm / virtio: Provide support " Pankaj Gupta
  9 siblings, 0 replies; 16+ messages in thread
From: Alexander Duyck @ 2019-08-21 15:00 UTC (permalink / raw)
  To: nitesh, kvm, mst, david, dave.hansen, linux-kernel, linux-mm,
	akpm, virtio-dev
  Cc: yang.zhang.wz, pagupta, riel, konrad.wilk, willy, lcapitulino,
	wei.w.wang, aarcange, pbonzini, dan.j.williams, mhocko,
	alexander.h.duyck, osalvador

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

Add support for what I am referring to as "unused 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 003b3ebcfdfb..7a30df63bc77 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -320,6 +320,40 @@ 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);
@@ -627,7 +661,8 @@ 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);
@@ -715,7 +750,8 @@ 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);
     }
 
@@ -805,6 +841,10 @@ 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,
@@ -931,6 +971,8 @@ 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] 16+ messages in thread

* Re: [PATCH v6 0/6] mm / virtio: Provide support for unused page reporting
  2019-08-21 14:59 [PATCH v6 0/6] mm / virtio: Provide support for unused page reporting Alexander Duyck
                   ` (8 preceding siblings ...)
  2019-08-21 15:00 ` [PATCH v6 QEMU 3/3] virtio-balloon: Provide a interface for " Alexander Duyck
@ 2019-08-22 10:43 ` " Pankaj Gupta
  2019-08-22 15:32   ` Alexander Duyck
  9 siblings, 1 reply; 16+ messages in thread
From: Pankaj Gupta @ 2019-08-22 10:43 UTC (permalink / raw)
  To: Alexander Duyck
  Cc: nitesh, kvm, mst, david, dave hansen, linux-kernel, willy,
	mhocko, linux-mm, akpm, virtio-dev, osalvador, yang zhang wz,
	riel, konrad wilk, lcapitulino, wei w wang, aarcange, pbonzini,
	dan j williams, alexander h duyck


> 
> This series provides an asynchronous means of reporting to a hypervisor
> that a guest page is no longer in use and can have the data associated
> with it dropped. To do this I have implemented functionality that allows
> for what I am referring to as unused page reporting
> 
> The functionality for this is fairly simple. When enabled it will allocate
> statistics to track the number of reported pages in a given free area.
> When the number of free pages exceeds this value plus a high water value,
> currently 32, it will begin performing page reporting which consists of
> pulling pages off of free list and placing them into a scatter list. The
> scatterlist is then given to the page reporting device and it will perform
> the required action to make the pages "reported", in the case of
> virtio-balloon this results in the pages being madvised as MADV_DONTNEED
> and as such they are forced out of the guest. After this they are placed
> back on the free list, and an additional bit is added if they are not
> merged indicating that they are a reported buddy page instead of a
> standard buddy page. The cycle then repeats with additional non-reported
> pages being pulled until the free areas all consist of reported pages.
> 
> I am leaving a number of things hard-coded such as limiting the lowest
> order processed to PAGEBLOCK_ORDER, and have left it up to the guest to
> determine what the limit is on how many pages it wants to allocate to
> process the hints. The upper limit for this is based on the size of the
> queue used to store the scattergather list.
> 
> My primary testing has just been to verify the memory is being freed after
> allocation by running memhog 40g on a 40g guest and watching the total
> free memory via /proc/meminfo on the host. With this I have verified most
> of the memory is freed after each iteration. 

I tried to go through the entire patch series. I can see you reported a
-3.27 drop from the baseline. If its because of re-faulting the page after
host has freed them? Can we avoid freeing all the pages from the guest free_area
and keep some pages(maybe some mixed order), so that next allocation is done from
the guest itself than faulting to host. This will work with real workload where
allocation and deallocation happen at regular intervals. 

This can be further optimized based on other factors like host memory pressure etc.

Thanks,
Pankaj       

As far as performance I have
> been mainly focusing on the will-it-scale/page_fault1 test running with
> 16 vcpus. I have modified it to use Transparent Huge Pages. With this I
> see almost no difference, -0.08%, with the patches applied and the feature
> disabled. I see a regression of -0.86% with the feature enabled, but the
> madvise disabled in the hypervisor due to a device being assigned. With
> the feature fully enabled I see a regression of -3.27% versus the baseline
> without these patches applied. In my testing I found that most of the
> overhead was due to the page zeroing that comes as a result of the pages
> having to be faulted back into the guest.
> 
> One side effect of these patches is that the guest becomes much more
> resilient in terms of NUMA locality. With the pages being freed and then
> reallocated when used it allows for the pages to be much closer to the
> active thread, and as a result there can be situations where this patch
> set will out-perform the stock kernel when the guest memory is not local
> to the guest vCPUs. To avoid that in my testing I set the affinity of all
> the vCPUs and QEMU instance to the same node.
> 
> Changes from the RFC:
> https://lore.kernel.org/lkml/20190530215223.13974.22445.stgit@localhost.localdomain/
> Moved aeration requested flag out of aerator and into zone->flags.
> Moved boundary out of free_area and into local variables for aeration.
> Moved aeration cycle out of interrupt and into workqueue.
> Left nr_free as total pages instead of splitting it between raw and aerated.
> Combined size and physical address values in virtio ring into one 64b value.
> 
> Changes from v1:
> https://lore.kernel.org/lkml/20190619222922.1231.27432.stgit@localhost.localdomain/
> Dropped "waste page treatment" in favor of "page hinting"
> Renamed files and functions from "aeration" to "page_hinting"
> Moved from page->lru list to scatterlist
> Replaced wait on refcnt in shutdown with RCU and cancel_delayed_work_sync
> Virtio now uses scatterlist directly instead of intermediate array
> Moved stats out of free_area, now in separate area and pointed to from zone
> Merged patch 5 into patch 4 to improve review-ability
> Updated various code comments throughout
> 
> Changes from v2:
> https://lore.kernel.org/lkml/20190724165158.6685.87228.stgit@localhost.localdomain/
> Dropped "page hinting" in favor of "page reporting"
> Renamed files from "hinting" to "reporting"
> Replaced "Hinted" page type with "Reported" page flag
> Added support for page poisoning while hinting is active
> Add QEMU patch that implements PAGE_POISON feature
> 
> Changes from v3:
> https://lore.kernel.org/lkml/20190801222158.22190.96964.stgit@localhost.localdomain/
> Added mutex lock around page reporting startup and shutdown
> Fixed reference to "page aeration" in patch 2
> Split page reporting function bit out into separate QEMU patch
> Limited capacity of scatterlist to vq size - 1 instead of vq size
> Added exception handling for case of virtio descriptor allocation failure
> 
> Changes from v4:
> https://lore.kernel.org/lkml/20190807224037.6891.53512.stgit@localhost.localdomain/
> Replaced spin_(un)lock with spin_(un)lock_irq in page_reporting_cycle()
> Dropped if/continue for ternary operator in page_reporting_process()
> Added checks for isolate and cma types to
> for_each_reporting_migratetype_order
> Added virtio-dev, Michal Hocko, and Oscar Salvador to to:/cc:
> Rebased on latest linux-next and QEMU git trees
> 
> Changes from v5:
> https://lore.kernel.org/lkml/20190812213158.22097.30576.stgit@localhost.localdomain/
> Replaced spin_(un)lock with spin_(un)lock_irq in page_reporting_startup()
> Updated shuffle code to use "shuffle_pick_tail" and updated patch description
> Dropped storage of order and migratettype while page is being reported
> Used get_pfnblock_migratetype to determine migratetype of page
> Renamed put_reported_page to free_reported_page, added order as argument
> Dropped check for CMA type as I believe we should be reporting those
> Added code to allow moving of reported pages into and out of isolation
> Defined page reporting order as minimum of Huge Page size vs MAX_ORDER - 1
> Cleaned up use of static branch usage for page_reporting_notify_enabled
> 
> ---
> 
> Alexander Duyck (6):
>       mm: Adjust shuffle code to allow for future coalescing
>       mm: Move set/get_pcppage_migratetype to mmzone.h
>       mm: Use zone and order instead of free area in free_list manipulators
>       mm: Introduce Reported pages
>       virtio-balloon: Pull page poisoning config out of free page hinting
>       virtio-balloon: Add support for providing unused page reports to host
> 
> 
>  drivers/virtio/Kconfig              |    1
>  drivers/virtio/virtio_balloon.c     |   84 ++++++++-
>  include/linux/mmzone.h              |  124 ++++++++-----
>  include/linux/page-flags.h          |   11 +
>  include/linux/page_reporting.h      |  177 ++++++++++++++++++
>  include/uapi/linux/virtio_balloon.h |    1
>  mm/Kconfig                          |    5 +
>  mm/Makefile                         |    1
>  mm/internal.h                       |   18 ++
>  mm/memory_hotplug.c                 |    1
>  mm/page_alloc.c                     |  216 ++++++++++++++++-------
>  mm/page_reporting.c                 |  336
>  +++++++++++++++++++++++++++++++++++
>  mm/shuffle.c                        |   40 +++-
>  mm/shuffle.h                        |   12 +
>  14 files changed, 896 insertions(+), 131 deletions(-)
>  create mode 100644 include/linux/page_reporting.h
>  create mode 100644 mm/page_reporting.c
> 
> --
> 
> 

^ permalink raw reply	[flat|nested] 16+ messages in thread

* Re: [PATCH v6 0/6] mm / virtio: Provide support for unused page reporting
  2019-08-22 10:43 ` [PATCH v6 0/6] mm / virtio: Provide support " Pankaj Gupta
@ 2019-08-22 15:32   ` Alexander Duyck
  2019-08-23  5:16     ` Pankaj Gupta
  0 siblings, 1 reply; 16+ messages in thread
From: Alexander Duyck @ 2019-08-22 15:32 UTC (permalink / raw)
  To: Pankaj Gupta, Alexander Duyck
  Cc: nitesh, kvm, mst, david, dave hansen, linux-kernel, willy,
	mhocko, linux-mm, akpm, virtio-dev, osalvador, yang zhang wz,
	riel, konrad wilk, lcapitulino, wei w wang, aarcange, pbonzini,
	dan j williams

On Thu, 2019-08-22 at 06:43 -0400, Pankaj Gupta wrote:
> > This series provides an asynchronous means of reporting to a hypervisor
> > that a guest page is no longer in use and can have the data associated
> > with it dropped. To do this I have implemented functionality that allows
> > for what I am referring to as unused page reporting
> > 
> > The functionality for this is fairly simple. When enabled it will allocate
> > statistics to track the number of reported pages in a given free area.
> > When the number of free pages exceeds this value plus a high water value,
> > currently 32, it will begin performing page reporting which consists of
> > pulling pages off of free list and placing them into a scatter list. The
> > scatterlist is then given to the page reporting device and it will perform
> > the required action to make the pages "reported", in the case of
> > virtio-balloon this results in the pages being madvised as MADV_DONTNEED
> > and as such they are forced out of the guest. After this they are placed
> > back on the free list, and an additional bit is added if they are not
> > merged indicating that they are a reported buddy page instead of a
> > standard buddy page. The cycle then repeats with additional non-reported
> > pages being pulled until the free areas all consist of reported pages.
> > 
> > I am leaving a number of things hard-coded such as limiting the lowest
> > order processed to PAGEBLOCK_ORDER, and have left it up to the guest to
> > determine what the limit is on how many pages it wants to allocate to
> > process the hints. The upper limit for this is based on the size of the
> > queue used to store the scattergather list.
> > 
> > My primary testing has just been to verify the memory is being freed after
> > allocation by running memhog 40g on a 40g guest and watching the total
> > free memory via /proc/meminfo on the host. With this I have verified most
> > of the memory is freed after each iteration. 
> 
> I tried to go through the entire patch series. I can see you reported a
> -3.27 drop from the baseline. If its because of re-faulting the page after
> host has freed them? Can we avoid freeing all the pages from the guest free_area
> and keep some pages(maybe some mixed order), so that next allocation is done from
> the guest itself than faulting to host. This will work with real workload where
> allocation and deallocation happen at regular intervals. 
> 
> This can be further optimized based on other factors like host memory pressure etc.
> 
> Thanks,
> Pankaj  

When I originally started implementing and testing this code I was seeing
less than a 1% regression. I didn't feel like that was really an accurate
result since it wasn't putting much stress on the changed code so I have
modified my tests and kernel so that I have memory shuffting and THP
enabled. In addition I have gone out of my way to lock things down to a
single NUMA node on my host system as the code I had would sometimes
perform better than baseline when running the test due to the fact that
memory was being freed back to the hose and then reallocated which
actually allowed for better NUMA locality.

The general idea was I wanted to know what the worst case penalty would be
for running this code, and it turns out most of that is just the cost of
faulting back in the pages. By enabling memory shuffling I am forcing the
memory to churn as pages are added to both the head and tail of the
free_list. The test itself was modified so that it didn't allocate order 0
pages and instead was allocating transparent huge pages so the effects
were as visible as possible. Without that the page faulting overhead would
mostly fall into the noise of having to allocate the memory as order 0
pages, that is what I had essentially seen earlier when I was running the
stock page_fault1 test.

This code does no hinting on anything smaller than either MAX_ORDER - 1 or
HUGETLB_PAGE_ORDER pages, and it only starts when there are at least 32 of
them available to hint on. This results in us not starting to perform the
hinting until there is 64MB to 128MB of memory sitting in the higher order
regions of the zone.

The hinting itself stops as soon as we run out of unhinted pages to pull
from. When this occurs we let any pages that are freed after that
accumulate until we get back to 32 pages being free in a given order.
During this time we should build up the cache of warm pages that you
mentioned, assuming that shuffling is not enabled.

As far as further optimizations I don't think there is anything here that
prevents us from doing that. For now I am focused on just getting the
basics in place so we have a foundation to start from.

Thanks.

- Alex


^ permalink raw reply	[flat|nested] 16+ messages in thread

* Re: [virtio-dev] [PATCH v6 4/6] mm: Introduce Reported pages
  2019-08-21 14:59 ` [PATCH v6 4/6] mm: Introduce Reported pages Alexander Duyck
@ 2019-08-22 16:18   ` " Nitesh Narayan Lal
  2019-08-22 16:24     ` Alexander Duyck
  0 siblings, 1 reply; 16+ messages in thread
From: Nitesh Narayan Lal @ 2019-08-22 16:18 UTC (permalink / raw)
  To: Alexander Duyck, kvm, mst, david, dave.hansen, linux-kernel,
	willy, mhocko, linux-mm, akpm, virtio-dev, osalvador
  Cc: yang.zhang.wz, pagupta, riel, konrad.wilk, lcapitulino,
	wei.w.wang, aarcange, pbonzini, dan.j.williams,
	alexander.h.duyck


On 8/21/19 10:59 AM, Alexander Duyck wrote:
> 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.
>
> It adds a set of pointers we shall call "boundary" which represents the
> upper boundary between the unreported and reported pages. The general idea
> is that in order for a page to cross from one side of the boundary to the
> other it will need to go through the reporting process. Ultimately a
> free_list has been fully processed when the boundary has been moved from
> the tail all they way up to occupying the first entry in the list.
>
> Doing this we should be able to make certain that we keep the reported
> pages as one contiguous block in each free list. This will allow us to
> efficiently manipulate the free lists whenever we need to go in and start
> sending reports to the hypervisor that there are new pages that have been
> freed and are no longer in use.
>
> An added advantage to this approach is that we should be reducing the
> overall memory footprint of the guest as it will be more likely to recycle
> warm pages versus trying to allocate the reported pages that were likely
> evicted from the guest memory.
>
> Since we will only be reporting one zone at a time we keep the boundary
> limited to being defined for just the zone we are currently reporting pages
> from. Doing this we can keep the number of additional pointers needed quite
> small. To flag that the boundaries are in place we use a single bit
> in the zone to indicate that reporting and the boundaries are active.
>
> The determination of when to start reporting is based on the tracking of
> the number of free pages in a given area versus the number of reported
> pages in that area. We keep track of the number of reported pages per
> free_area in a separate zone specific area. We do this to avoid modifying
> the free_area structure as this can lead to false sharing for the highest
> order with the zone lock which leads to a noticeable performance
> degradation.
[...]
> +
> +/* request page reporting on this zone */
> +void __page_reporting_request(struct zone *zone)
> +{
> +	struct page_reporting_dev_info *phdev;
> +
> +	rcu_read_lock();
> +
> +	/*
> +	 * We use RCU to protect the ph_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.
> +	 */
> +	phdev = rcu_dereference(ph_dev_info);
> +	if (unlikely(!phdev))
> +		return;
> +

Just a minor comment here.
Although this is unlikely to trigger still I think you should release the
rcu_read_lock before returning.

> +	/*
> +	 * We can use separate test and set operations here as there
> +	 * is nothing else that can set or clear this bit while we are
> +	 * holding the zone lock. The advantage to doing it this way is
> +	 * that we don't have to dirty the cacheline unless we are
> +	 * changing the value.
> +	 */
> +	__set_bit(ZONE_PAGE_REPORTING_REQUESTED, &zone->flags);
> +
> +	/*
> +	 * Delay the start of work to allow a sizable queue to
> +	 * build. For now we are limiting this to running no more
> +	 * than 10 times per second.
> +	 */
> +	if (!atomic_fetch_inc(&phdev->refcnt))
> +		schedule_delayed_work(&phdev->work, HZ / 10);
> +
> +	rcu_read_unlock();
> +}
> +
[...]
> +	}
> +
> +	/* enable page reporting notification */
> +	static_branch_enable(&page_reporting_notify_enabled);
> +err_out:
> +	mutex_unlock(&page_reporting_mutex);
> +
> +	return err;
> +}
> +EXPORT_SYMBOL_GPL(page_reporting_startup);
>
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org
> For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org
>
-- 
Thanks
Nitesh


^ permalink raw reply	[flat|nested] 16+ messages in thread

* Re: [virtio-dev] [PATCH v6 4/6] mm: Introduce Reported pages
  2019-08-22 16:18   ` [virtio-dev] " Nitesh Narayan Lal
@ 2019-08-22 16:24     ` Alexander Duyck
  0 siblings, 0 replies; 16+ messages in thread
From: Alexander Duyck @ 2019-08-22 16:24 UTC (permalink / raw)
  To: Nitesh Narayan Lal
  Cc: kvm list, Michael S. Tsirkin, David Hildenbrand, Dave Hansen,
	LKML, Matthew Wilcox, Michal Hocko, linux-mm, Andrew Morton,
	virtio-dev, Oscar Salvador, Yang Zhang, Pankaj Gupta,
	Rik van Riel, Konrad Rzeszutek Wilk, lcapitulino, Wang, Wei W,
	Andrea Arcangeli, Paolo Bonzini, Dan Williams, Alexander Duyck

On Thu, Aug 22, 2019 at 9:19 AM Nitesh Narayan Lal <nitesh@redhat.com> wrote:
>
>
> On 8/21/19 10:59 AM, Alexander Duyck wrote:
> > 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.
> >
> > It adds a set of pointers we shall call "boundary" which represents the
> > upper boundary between the unreported and reported pages. The general idea
> > is that in order for a page to cross from one side of the boundary to the
> > other it will need to go through the reporting process. Ultimately a
> > free_list has been fully processed when the boundary has been moved from
> > the tail all they way up to occupying the first entry in the list.
> >
> > Doing this we should be able to make certain that we keep the reported
> > pages as one contiguous block in each free list. This will allow us to
> > efficiently manipulate the free lists whenever we need to go in and start
> > sending reports to the hypervisor that there are new pages that have been
> > freed and are no longer in use.
> >
> > An added advantage to this approach is that we should be reducing the
> > overall memory footprint of the guest as it will be more likely to recycle
> > warm pages versus trying to allocate the reported pages that were likely
> > evicted from the guest memory.
> >
> > Since we will only be reporting one zone at a time we keep the boundary
> > limited to being defined for just the zone we are currently reporting pages
> > from. Doing this we can keep the number of additional pointers needed quite
> > small. To flag that the boundaries are in place we use a single bit
> > in the zone to indicate that reporting and the boundaries are active.
> >
> > The determination of when to start reporting is based on the tracking of
> > the number of free pages in a given area versus the number of reported
> > pages in that area. We keep track of the number of reported pages per
> > free_area in a separate zone specific area. We do this to avoid modifying
> > the free_area structure as this can lead to false sharing for the highest
> > order with the zone lock which leads to a noticeable performance
> > degradation.
> [...]
> > +
> > +/* request page reporting on this zone */
> > +void __page_reporting_request(struct zone *zone)
> > +{
> > +     struct page_reporting_dev_info *phdev;
> > +
> > +     rcu_read_lock();
> > +
> > +     /*
> > +      * We use RCU to protect the ph_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.
> > +      */
> > +     phdev = rcu_dereference(ph_dev_info);
> > +     if (unlikely(!phdev))
> > +             return;
> > +
>
> Just a minor comment here.
> Although this is unlikely to trigger still I think you should release the
> rcu_read_lock before returning.

Thanks for catching that. I will have that fixed for next version.

- Alex

^ permalink raw reply	[flat|nested] 16+ messages in thread

* Re: [PATCH v6 0/6] mm / virtio: Provide support for unused page reporting
  2019-08-22 15:32   ` Alexander Duyck
@ 2019-08-23  5:16     ` Pankaj Gupta
  2019-08-23 15:02       ` Alexander Duyck
  0 siblings, 1 reply; 16+ messages in thread
From: Pankaj Gupta @ 2019-08-23  5:16 UTC (permalink / raw)
  To: Alexander Duyck
  Cc: Alexander Duyck, nitesh, kvm, mst, david, dave hansen,
	linux-kernel, willy, mhocko, linux-mm, akpm, virtio-dev,
	osalvador, yang zhang wz, riel, konrad wilk, lcapitulino,
	wei w wang, aarcange, pbonzini, dan j williams


> On Thu, 2019-08-22 at 06:43 -0400, Pankaj Gupta wrote:
> > > This series provides an asynchronous means of reporting to a hypervisor
> > > that a guest page is no longer in use and can have the data associated
> > > with it dropped. To do this I have implemented functionality that allows
> > > for what I am referring to as unused page reporting
> > > 
> > > The functionality for this is fairly simple. When enabled it will
> > > allocate
> > > statistics to track the number of reported pages in a given free area.
> > > When the number of free pages exceeds this value plus a high water value,
> > > currently 32, it will begin performing page reporting which consists of
> > > pulling pages off of free list and placing them into a scatter list. The
> > > scatterlist is then given to the page reporting device and it will
> > > perform
> > > the required action to make the pages "reported", in the case of
> > > virtio-balloon this results in the pages being madvised as MADV_DONTNEED
> > > and as such they are forced out of the guest. After this they are placed
> > > back on the free list, and an additional bit is added if they are not
> > > merged indicating that they are a reported buddy page instead of a
> > > standard buddy page. The cycle then repeats with additional non-reported
> > > pages being pulled until the free areas all consist of reported pages.
> > > 
> > > I am leaving a number of things hard-coded such as limiting the lowest
> > > order processed to PAGEBLOCK_ORDER, and have left it up to the guest to
> > > determine what the limit is on how many pages it wants to allocate to
> > > process the hints. The upper limit for this is based on the size of the
> > > queue used to store the scattergather list.
> > > 
> > > My primary testing has just been to verify the memory is being freed
> > > after
> > > allocation by running memhog 40g on a 40g guest and watching the total
> > > free memory via /proc/meminfo on the host. With this I have verified most
> > > of the memory is freed after each iteration.
> > 
> > I tried to go through the entire patch series. I can see you reported a
> > -3.27 drop from the baseline. If its because of re-faulting the page after
> > host has freed them? Can we avoid freeing all the pages from the guest
> > free_area
> > and keep some pages(maybe some mixed order), so that next allocation is
> > done from
> > the guest itself than faulting to host. This will work with real workload
> > where
> > allocation and deallocation happen at regular intervals.
> > 
> > This can be further optimized based on other factors like host memory
> > pressure etc.
> > 
> > Thanks,
> > Pankaj
> 
> When I originally started implementing and testing this code I was seeing
> less than a 1% regression. I didn't feel like that was really an accurate
> result since it wasn't putting much stress on the changed code so I have
> modified my tests and kernel so that I have memory shuffting and THP
> enabled. In addition I have gone out of my way to lock things down to a
> single NUMA node on my host system as the code I had would sometimes
> perform better than baseline when running the test due to the fact that
> memory was being freed back to the hose and then reallocated which
> actually allowed for better NUMA locality.
> 
> The general idea was I wanted to know what the worst case penalty would be
> for running this code, and it turns out most of that is just the cost of
> faulting back in the pages. By enabling memory shuffling I am forcing the
> memory to churn as pages are added to both the head and tail of the
> free_list. The test itself was modified so that it didn't allocate order 0
> pages and instead was allocating transparent huge pages so the effects
> were as visible as possible. Without that the page faulting overhead would
> mostly fall into the noise of having to allocate the memory as order 0
> pages, that is what I had essentially seen earlier when I was running the
> stock page_fault1 test.

Right. I think the reason is this test is allocating THP's in guest, host side
you are still using order 0 pages, I assume?

> 
> This code does no hinting on anything smaller than either MAX_ORDER - 1 or
> HUGETLB_PAGE_ORDER pages, and it only starts when there are at least 32 of
> them available to hint on. This results in us not starting to perform the
> hinting until there is 64MB to 128MB of memory sitting in the higher order
> regions of the zone.

o.k

> 
> The hinting itself stops as soon as we run out of unhinted pages to pull
> from. When this occurs we let any pages that are freed after that
> accumulate until we get back to 32 pages being free in a given order.
> During this time we should build up the cache of warm pages that you
> mentioned, assuming that shuffling is not enabled.

I was thinking about something like retaining pages to a lower watermark here.
Looks like we still might have few lower order pages in free list if they are
not merged to orders which are hinted. 

> 
> As far as further optimizations I don't think there is anything here that
> prevents us from doing that. For now I am focused on just getting the
> basics in place so we have a foundation to start from.

Agree. Thanks for explaining.

Best rgards,
Pankaj

> 
> Thanks.
> 
> - Alex
> 
> 

^ permalink raw reply	[flat|nested] 16+ messages in thread

* Re: [PATCH v6 0/6] mm / virtio: Provide support for unused page reporting
  2019-08-23  5:16     ` Pankaj Gupta
@ 2019-08-23 15:02       ` Alexander Duyck
  0 siblings, 0 replies; 16+ messages in thread
From: Alexander Duyck @ 2019-08-23 15:02 UTC (permalink / raw)
  To: Pankaj Gupta
  Cc: Alexander Duyck, nitesh, kvm, mst, david, dave hansen,
	linux-kernel, willy, mhocko, linux-mm, akpm, virtio-dev,
	osalvador, yang zhang wz, riel, konrad wilk, lcapitulino,
	wei w wang, aarcange, pbonzini, dan j williams

On Fri, 2019-08-23 at 01:16 -0400, Pankaj Gupta wrote:
> > On Thu, 2019-08-22 at 06:43 -0400, Pankaj Gupta wrote:
> > > > This series provides an asynchronous means of reporting to a hypervisor
> > > > that a guest page is no longer in use and can have the data associated
> > > > with it dropped. To do this I have implemented functionality that allows
> > > > for what I am referring to as unused page reporting
> > > > 
> > > > The functionality for this is fairly simple. When enabled it will
> > > > allocate
> > > > statistics to track the number of reported pages in a given free area.
> > > > When the number of free pages exceeds this value plus a high water value,
> > > > currently 32, it will begin performing page reporting which consists of
> > > > pulling pages off of free list and placing them into a scatter list. The
> > > > scatterlist is then given to the page reporting device and it will
> > > > perform
> > > > the required action to make the pages "reported", in the case of
> > > > virtio-balloon this results in the pages being madvised as MADV_DONTNEED
> > > > and as such they are forced out of the guest. After this they are placed
> > > > back on the free list, and an additional bit is added if they are not
> > > > merged indicating that they are a reported buddy page instead of a
> > > > standard buddy page. The cycle then repeats with additional non-reported
> > > > pages being pulled until the free areas all consist of reported pages.
> > > > 
> > > > I am leaving a number of things hard-coded such as limiting the lowest
> > > > order processed to PAGEBLOCK_ORDER, and have left it up to the guest to
> > > > determine what the limit is on how many pages it wants to allocate to
> > > > process the hints. The upper limit for this is based on the size of the
> > > > queue used to store the scattergather list.
> > > > 
> > > > My primary testing has just been to verify the memory is being freed
> > > > after
> > > > allocation by running memhog 40g on a 40g guest and watching the total
> > > > free memory via /proc/meminfo on the host. With this I have verified most
> > > > of the memory is freed after each iteration.
> > > 
> > > I tried to go through the entire patch series. I can see you reported a
> > > -3.27 drop from the baseline. If its because of re-faulting the page after
> > > host has freed them? Can we avoid freeing all the pages from the guest
> > > free_area
> > > and keep some pages(maybe some mixed order), so that next allocation is
> > > done from
> > > the guest itself than faulting to host. This will work with real workload
> > > where
> > > allocation and deallocation happen at regular intervals.
> > > 
> > > This can be further optimized based on other factors like host memory
> > > pressure etc.
> > > 
> > > Thanks,
> > > Pankaj
> > 
> > When I originally started implementing and testing this code I was seeing
> > less than a 1% regression. I didn't feel like that was really an accurate
> > result since it wasn't putting much stress on the changed code so I have
> > modified my tests and kernel so that I have memory shuffting and THP
> > enabled. In addition I have gone out of my way to lock things down to a
> > single NUMA node on my host system as the code I had would sometimes
> > perform better than baseline when running the test due to the fact that
> > memory was being freed back to the hose and then reallocated which
> > actually allowed for better NUMA locality.
> > 
> > The general idea was I wanted to know what the worst case penalty would be
> > for running this code, and it turns out most of that is just the cost of
> > faulting back in the pages. By enabling memory shuffling I am forcing the
> > memory to churn as pages are added to both the head and tail of the
> > free_list. The test itself was modified so that it didn't allocate order 0
> > pages and instead was allocating transparent huge pages so the effects
> > were as visible as possible. Without that the page faulting overhead would
> > mostly fall into the noise of having to allocate the memory as order 0
> > pages, that is what I had essentially seen earlier when I was running the
> > stock page_fault1 test.
> 
> Right. I think the reason is this test is allocating THP's in guest, host side
> you are still using order 0 pages, I assume?

No, on host side they should be huge pages as well. Most of the cost for
the fault is the page zeroing I believe since we are having to zero a 2MB
page twice, once in the host and once in the guest.

Basically if I disable THP in the guest the results are roughly half what
they are with THP enabled, and the difference between the patchset and
baseline drops to less than 1%.

> > This code does no hinting on anything smaller than either MAX_ORDER - 1 or
> > HUGETLB_PAGE_ORDER pages, and it only starts when there are at least 32 of
> > them available to hint on. This results in us not starting to perform the
> > hinting until there is 64MB to 128MB of memory sitting in the higher order
> > regions of the zone.
> 
> o.k
> 
> > The hinting itself stops as soon as we run out of unhinted pages to pull
> > from. When this occurs we let any pages that are freed after that
> > accumulate until we get back to 32 pages being free in a given order.
> > During this time we should build up the cache of warm pages that you
> > mentioned, assuming that shuffling is not enabled.
> 
> I was thinking about something like retaining pages to a lower watermark here.
> Looks like we still might have few lower order pages in free list if they are
> not merged to orders which are hinted. 

Right. We should have everything below the reporting order untouched and
as such it will not be faulted. It is only if the page gets merged back up
to reporting order that we will reported it, and only if we have at least
32 of them available.

> > As far as further optimizations I don't think there is anything here that
> > prevents us from doing that. For now I am focused on just getting the
> > basics in place so we have a foundation to start from.
> 
> Agree. Thanks for explaining.
> 
> Best rgards,
> Pankaj

Thanks.

- Alex


^ permalink raw reply	[flat|nested] 16+ messages in thread

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Thread overview: 16+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-08-21 14:59 [PATCH v6 0/6] mm / virtio: Provide support for unused page reporting Alexander Duyck
2019-08-21 14:59 ` [PATCH v6 1/6] mm: Adjust shuffle code to allow for future coalescing Alexander Duyck
2019-08-21 14:59 ` [PATCH v6 2/6] mm: Move set/get_pcppage_migratetype to mmzone.h Alexander Duyck
2019-08-21 14:59 ` [PATCH v6 3/6] mm: Use zone and order instead of free area in free_list manipulators Alexander Duyck
2019-08-21 14:59 ` [PATCH v6 4/6] mm: Introduce Reported pages Alexander Duyck
2019-08-22 16:18   ` [virtio-dev] " Nitesh Narayan Lal
2019-08-22 16:24     ` Alexander Duyck
2019-08-21 14:59 ` [PATCH v6 5/6] virtio-balloon: Pull page poisoning config out of free page hinting Alexander Duyck
2019-08-21 15:00 ` [PATCH v6 6/6] virtio-balloon: Add support for providing unused page reports to host Alexander Duyck
2019-08-21 15:00 ` [PATCH v6 QEMU 1/3] virtio-ballon: Implement support for page poison tracking feature Alexander Duyck
2019-08-21 15:00 ` [PATCH v6 QEMU 2/3] virtio-balloon: Add bit to notify guest of unused page reporting Alexander Duyck
2019-08-21 15:00 ` [PATCH v6 QEMU 3/3] virtio-balloon: Provide a interface for " Alexander Duyck
2019-08-22 10:43 ` [PATCH v6 0/6] mm / virtio: Provide support " Pankaj Gupta
2019-08-22 15:32   ` Alexander Duyck
2019-08-23  5:16     ` Pankaj Gupta
2019-08-23 15:02       ` Alexander Duyck

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