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* [PATCH v2 0/5] mm: place pages to the freelist tail when onlining and undoing isolation
@ 2020-10-05 12:15 David Hildenbrand
  2020-10-05 12:15 ` [PATCH v2 1/5] mm/page_alloc: convert "report" flag of __free_one_page() to a proper flag David Hildenbrand
                   ` (4 more replies)
  0 siblings, 5 replies; 11+ messages in thread
From: David Hildenbrand @ 2020-10-05 12:15 UTC (permalink / raw)
  To: linux-kernel
  Cc: linux-mm, linux-hyperv, xen-devel, linux-acpi, Andrew Morton,
	Matthew Wilcox, David Hildenbrand, Alexander Duyck, Dave Hansen,
	Haiyang Zhang, K. Y. Srinivasan, Mel Gorman, Michael Ellerman,
	Michal Hocko, Michal Hocko, Mike Rapoport, Oscar Salvador,
	Pankaj Gupta, Scott Cheloha, Stephen Hemminger, Vlastimil Babka,
	Wei Liu, Wei Yang

When adding separate memory blocks via add_memory*() and onlining them
immediately, the metadata (especially the memmap) of the next block will be
placed onto one of the just added+onlined block. This creates a chain
of unmovable allocations: If the last memory block cannot get
offlined+removed() so will all dependent ones. We directly have unmovable
allocations all over the place.

This can be observed quite easily using virtio-mem, however, it can also
be observed when using DIMMs. The freshly onlined pages will usually be
placed to the head of the freelists, meaning they will be allocated next,
turning the just-added memory usually immediately un-removable. The
fresh pages are cold, prefering to allocate others (that might be hot)
also feels to be the natural thing to do.

It also applies to the hyper-v balloon xen-balloon, and ppc64 dlpar: when
adding separate, successive memory blocks, each memory block will have
unmovable allocations on them - for example gigantic pages will fail to
allocate.

While the ZONE_NORMAL doesn't provide any guarantees that memory can get
offlined+removed again (any kind of fragmentation with unmovable
allocations is possible), there are many scenarios (hotplugging a lot of
memory, running workload, hotunplug some memory/as much as possible) where
we can offline+remove quite a lot with this patchset.

a) To visualize the problem, a very simple example:

Start a VM with 4GB and 8GB of virtio-mem memory:

 [root@localhost ~]# lsmem
 RANGE                                 SIZE  STATE REMOVABLE  BLOCK
 0x0000000000000000-0x00000000bfffffff   3G online       yes   0-23
 0x0000000100000000-0x000000033fffffff   9G online       yes 32-103

 Memory block size:       128M
 Total online memory:      12G
 Total offline memory:      0B

Then try to unplug as much as possible using virtio-mem. Observe which
memory blocks are still around. Without this patch set:

 [root@localhost ~]# lsmem
 RANGE                                  SIZE  STATE REMOVABLE   BLOCK
 0x0000000000000000-0x00000000bfffffff    3G online       yes    0-23
 0x0000000100000000-0x000000013fffffff    1G online       yes   32-39
 0x0000000148000000-0x000000014fffffff  128M online       yes      41
 0x0000000158000000-0x000000015fffffff  128M online       yes      43
 0x0000000168000000-0x000000016fffffff  128M online       yes      45
 0x0000000178000000-0x000000017fffffff  128M online       yes      47
 0x0000000188000000-0x0000000197ffffff  256M online       yes   49-50
 0x00000001a0000000-0x00000001a7ffffff  128M online       yes      52
 0x00000001b0000000-0x00000001b7ffffff  128M online       yes      54
 0x00000001c0000000-0x00000001c7ffffff  128M online       yes      56
 0x00000001d0000000-0x00000001d7ffffff  128M online       yes      58
 0x00000001e0000000-0x00000001e7ffffff  128M online       yes      60
 0x00000001f0000000-0x00000001f7ffffff  128M online       yes      62
 0x0000000200000000-0x0000000207ffffff  128M online       yes      64
 0x0000000210000000-0x0000000217ffffff  128M online       yes      66
 0x0000000220000000-0x0000000227ffffff  128M online       yes      68
 0x0000000230000000-0x0000000237ffffff  128M online       yes      70
 0x0000000240000000-0x0000000247ffffff  128M online       yes      72
 0x0000000250000000-0x0000000257ffffff  128M online       yes      74
 0x0000000260000000-0x0000000267ffffff  128M online       yes      76
 0x0000000270000000-0x0000000277ffffff  128M online       yes      78
 0x0000000280000000-0x0000000287ffffff  128M online       yes      80
 0x0000000290000000-0x0000000297ffffff  128M online       yes      82
 0x00000002a0000000-0x00000002a7ffffff  128M online       yes      84
 0x00000002b0000000-0x00000002b7ffffff  128M online       yes      86
 0x00000002c0000000-0x00000002c7ffffff  128M online       yes      88
 0x00000002d0000000-0x00000002d7ffffff  128M online       yes      90
 0x00000002e0000000-0x00000002e7ffffff  128M online       yes      92
 0x00000002f0000000-0x00000002f7ffffff  128M online       yes      94
 0x0000000300000000-0x0000000307ffffff  128M online       yes      96
 0x0000000310000000-0x0000000317ffffff  128M online       yes      98
 0x0000000320000000-0x0000000327ffffff  128M online       yes     100
 0x0000000330000000-0x000000033fffffff  256M online       yes 102-103

 Memory block size:       128M
 Total online memory:     8.1G
 Total offline memory:      0B

With this patch set:

 [root@localhost ~]# lsmem
 RANGE                                 SIZE  STATE REMOVABLE BLOCK
 0x0000000000000000-0x00000000bfffffff   3G online       yes  0-23
 0x0000000100000000-0x000000013fffffff   1G online       yes 32-39

 Memory block size:       128M
 Total online memory:       4G
 Total offline memory:      0B

All memory can get unplugged, all memory block can get removed. Of course,
no workload ran and the system was basically idle, but it highlights the
issue - the fairly deterministic chain of unmovable allocations. When a
huge page for the 2MB memmap is needed, a just-onlined 4MB page will
be split. The remaining 2MB page will be used for the memmap of the next
memory block. So one memory block will hold the memmap of the two following
memory blocks. Finally the pages of the last-onlined memory block will get
used for the next bigger allocations - if any allocation is unmovable,
all dependent memory blocks cannot get unplugged and removed until that
allocation is gone.

Note that with bigger memory blocks (e.g., 256MB), *all* memory
blocks are dependent and none can get unplugged again!

b) Experiment with memory intensive workload

I performed an experiment with an older version of this patch set
(before we used undo_isolate_page_range() in online_pages():
Hotplug 56GB to a VM with an initial 4GB, onlining all memory to
ZONE_NORMAL right from the kernel when adding it. I then run various
memory intensive workloads that consume most system memory for a total of
45 minutes. Once finished, I try to unplug as much memory as possible.

With this change, I am able to remove via virtio-mem (adding individual
128MB memory blocks) 413 out of 448 added memory blocks. Via individual
(256MB) DIMMs 380 out of 448 added memory blocks. (I don't have any numbers
without this patchset, but looking at the above example, it's at most half
of the 448 memory blocks for virtio-mem, and most probably none for DIMMs).

Again, there are workloads that might behave very differently due to the
nature of ZONE_NORMAL.

This change also affects (besodes memory onlining):
- Other users of undo_isolate_page_range(): Pages are always placed to the
  tail.
-- When memory offlining fails
-- When memory isolation fails after having isolated some pageblocks
-- When alloc_contig_range() either succeeds or fails
- Other users of __putback_isolated_page(): Pages are always placed to the
  tail.
-- Free page reporting
- Other users of __free_pages_core()
-- AFAIKs, any memory that is getting exposed to the buddy during boot.
   IIUC we will now usually allocate memory from lower addresses within
   a zone first (especially during boot).
- Other users of generic_online_page()
-- Hyper-V balloon

v1 -> v2:
- Avoid changing indentation/alignment of function parameters
- Minor spelling fixes
- "mm/page_alloc: convert "report" flag of __free_one_page() to a proper
   flag"
-- fop_t -> fpi_t
-- Clarify/extend documentation of FPI_SKIP_REPORT_NOTIFY
- "mm/page_alloc: move pages to tail in move_to_free_list()"
-- Perform change for all move_to_free_list()/move_freepages_block() users
   to simplify.
-- Adjust subject/description accordingly.
- "mm/page_alloc: place pages to tail in __free_pages_core()"
-- s/init_single_page/__init_single_page/

RFC -> v1:
- Tweak some patch descriptions
- "mm/page_alloc: place pages to tail in __putback_isolated_page()"
-- FOP_TO_TAIL now has higher precedence than page shuffling
-- Add a note that nothing should rely on FOP_TO_TAIL for correctness
- "mm/page_alloc: always move pages to the tail of the freelist in
   unset_migratetype_isolate()"
-- Use "bool" parameter for move_freepages_block() as requested
- "mm/page_alloc: place pages to tail in __free_pages_core()"
-- Eliminate set_page_refcounted() + page_ref_dec() and add a comment
- "mm/memory_hotplug: update comment regarding zone shuffling"
-- Added

David Hildenbrand (5):
  mm/page_alloc: convert "report" flag of __free_one_page() to a proper
    flag
  mm/page_alloc: place pages to tail in __putback_isolated_page()
  mm/page_alloc: move pages to tail in move_to_free_list()
  mm/page_alloc: place pages to tail in __free_pages_core()
  mm/memory_hotplug: update comment regarding zone shuffling

 mm/memory_hotplug.c | 11 +++---
 mm/page_alloc.c     | 84 +++++++++++++++++++++++++++++++++++----------
 mm/page_isolation.c |  5 +++
 3 files changed, 75 insertions(+), 25 deletions(-)

-- 
2.26.2


^ permalink raw reply	[flat|nested] 11+ messages in thread

* [PATCH v2 1/5] mm/page_alloc: convert "report" flag of __free_one_page() to a proper flag
  2020-10-05 12:15 [PATCH v2 0/5] mm: place pages to the freelist tail when onlining and undoing isolation David Hildenbrand
@ 2020-10-05 12:15 ` David Hildenbrand
  2020-10-05 12:15 ` [PATCH v2 2/5] mm/page_alloc: place pages to tail in __putback_isolated_page() David Hildenbrand
                   ` (3 subsequent siblings)
  4 siblings, 0 replies; 11+ messages in thread
From: David Hildenbrand @ 2020-10-05 12:15 UTC (permalink / raw)
  To: linux-kernel
  Cc: linux-mm, linux-hyperv, xen-devel, linux-acpi, Andrew Morton,
	Matthew Wilcox, David Hildenbrand, Alexander Duyck,
	Vlastimil Babka, Oscar Salvador, Wei Yang, Pankaj Gupta,
	Michal Hocko, Mel Gorman, Michal Hocko, Dave Hansen,
	Mike Rapoport

Let's prepare for additional flags and avoid long parameter lists of bools.
Follow-up patches will also make use of the flags in __free_pages_ok().

Reviewed-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Mike Rapoport <rppt@kernel.org>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/page_alloc.c | 27 ++++++++++++++++++++++-----
 1 file changed, 22 insertions(+), 5 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7012d67a302d..2bf235b1953f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -78,6 +78,22 @@
 #include "shuffle.h"
 #include "page_reporting.h"
 
+/* Free Page Internal flags: for internal, non-pcp variants of free_pages(). */
+typedef int __bitwise fpi_t;
+
+/* No special request */
+#define FPI_NONE		((__force fpi_t)0)
+
+/*
+ * Skip free page reporting notification for the (possibly merged) page.
+ * This does not hinder free page reporting from grabbing the page,
+ * reporting it and marking it "reported" -  it only skips notifying
+ * the free page reporting infrastructure about a newly freed page. For
+ * example, used when temporarily pulling a page from a freelist and
+ * putting it back unmodified.
+ */
+#define FPI_SKIP_REPORT_NOTIFY	((__force fpi_t)BIT(0))
+
 /* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
 static DEFINE_MUTEX(pcp_batch_high_lock);
 #define MIN_PERCPU_PAGELIST_FRACTION	(8)
@@ -952,7 +968,7 @@ buddy_merge_likely(unsigned long pfn, unsigned long buddy_pfn,
 static inline void __free_one_page(struct page *page,
 		unsigned long pfn,
 		struct zone *zone, unsigned int order,
-		int migratetype, bool report)
+		int migratetype, fpi_t fpi_flags)
 {
 	struct capture_control *capc = task_capc(zone);
 	unsigned long buddy_pfn;
@@ -1039,7 +1055,7 @@ static inline void __free_one_page(struct page *page,
 		add_to_free_list(page, zone, order, migratetype);
 
 	/* Notify page reporting subsystem of freed page */
-	if (report)
+	if (!(fpi_flags & FPI_SKIP_REPORT_NOTIFY))
 		page_reporting_notify_free(order);
 }
 
@@ -1380,7 +1396,7 @@ 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, true);
+		__free_one_page(page, page_to_pfn(page), zone, 0, mt, FPI_NONE);
 		trace_mm_page_pcpu_drain(page, 0, mt);
 	}
 	spin_unlock(&zone->lock);
@@ -1396,7 +1412,7 @@ 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, true);
+	__free_one_page(page, pfn, zone, order, migratetype, FPI_NONE);
 	spin_unlock(&zone->lock);
 }
 
@@ -3289,7 +3305,8 @@ void __putback_isolated_page(struct page *page, unsigned int order, int mt)
 	lockdep_assert_held(&zone->lock);
 
 	/* Return isolated page to tail of freelist. */
-	__free_one_page(page, page_to_pfn(page), zone, order, mt, false);
+	__free_one_page(page, page_to_pfn(page), zone, order, mt,
+			FPI_SKIP_REPORT_NOTIFY);
 }
 
 /*
-- 
2.26.2


^ permalink raw reply	[flat|nested] 11+ messages in thread

* [PATCH v2 2/5] mm/page_alloc: place pages to tail in __putback_isolated_page()
  2020-10-05 12:15 [PATCH v2 0/5] mm: place pages to the freelist tail when onlining and undoing isolation David Hildenbrand
  2020-10-05 12:15 ` [PATCH v2 1/5] mm/page_alloc: convert "report" flag of __free_one_page() to a proper flag David Hildenbrand
@ 2020-10-05 12:15 ` David Hildenbrand
  2020-10-20 17:18   ` Vlastimil Babka
  2020-10-05 12:15 ` [PATCH v2 3/5] mm/page_alloc: move pages to tail in move_to_free_list() David Hildenbrand
                   ` (2 subsequent siblings)
  4 siblings, 1 reply; 11+ messages in thread
From: David Hildenbrand @ 2020-10-05 12:15 UTC (permalink / raw)
  To: linux-kernel
  Cc: linux-mm, linux-hyperv, xen-devel, linux-acpi, Andrew Morton,
	Matthew Wilcox, David Hildenbrand, Alexander Duyck,
	Oscar Salvador, Wei Yang, Pankaj Gupta, Michal Hocko, Mel Gorman,
	Michal Hocko, Dave Hansen, Vlastimil Babka, Mike Rapoport,
	Scott Cheloha, Michael Ellerman

__putback_isolated_page() already documents that pages will be placed to
the tail of the freelist - this is, however, not the case for
"order >= MAX_ORDER - 2" (see buddy_merge_likely()) - which should be
the case for all existing users.

This change affects two users:
- free page reporting
- page isolation, when undoing the isolation (including memory onlining).

This behavior is desireable for pages that haven't really been touched
lately, so exactly the two users that don't actually read/write page
content, but rather move untouched pages.

The new behavior is especially desirable for memory onlining, where we
allow allocation of newly onlined pages via undo_isolate_page_range()
in online_pages(). Right now, we always place them to the head of the
freelist, resulting in undesireable behavior: Assume we add
individual memory chunks via add_memory() and online them right away to
the NORMAL zone. We create a dependency chain of unmovable allocations
e.g., via the memmap. The memmap of the next chunk will be placed onto
previous chunks - if the last block cannot get offlined+removed, all
dependent ones cannot get offlined+removed. While this can already be
observed with individual DIMMs, it's more of an issue for virtio-mem
(and I suspect also ppc DLPAR).

Document that this should only be used for optimizations, and no code
should rely on this behavior for correction (if the order of the
freelists ever changes).

We won't care about page shuffling: memory onlining already properly
shuffles after onlining. free page reporting doesn't care about
physically contiguous ranges, and there are already cases where page
isolation will simply move (physically close) free pages to (currently)
the head of the freelists via move_freepages_block() instead of
shuffling. If this becomes ever relevant, we should shuffle the whole
zone when undoing isolation of larger ranges, and after
free_contig_range().

Reviewed-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Scott Cheloha <cheloha@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/page_alloc.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2bf235b1953f..df5ff0cd6df1 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -94,6 +94,18 @@ typedef int __bitwise fpi_t;
  */
 #define FPI_SKIP_REPORT_NOTIFY	((__force fpi_t)BIT(0))
 
+/*
+ * Place the (possibly merged) page to the tail of the freelist. Will ignore
+ * page shuffling (relevant code - e.g., memory onlining - is expected to
+ * shuffle the whole zone).
+ *
+ * Note: No code should rely on this flag for correctness - it's purely
+ *       to allow for optimizations when handing back either fresh pages
+ *       (memory onlining) or untouched pages (page isolation, free page
+ *       reporting).
+ */
+#define FPI_TO_TAIL		((__force fpi_t)BIT(1))
+
 /* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
 static DEFINE_MUTEX(pcp_batch_high_lock);
 #define MIN_PERCPU_PAGELIST_FRACTION	(8)
@@ -1044,7 +1056,9 @@ static inline void __free_one_page(struct page *page,
 done_merging:
 	set_page_order(page, order);
 
-	if (is_shuffle_order(order))
+	if (fpi_flags & FPI_TO_TAIL)
+		to_tail = true;
+	else if (is_shuffle_order(order))
 		to_tail = shuffle_pick_tail();
 	else
 		to_tail = buddy_merge_likely(pfn, buddy_pfn, page, order);
@@ -3306,7 +3320,7 @@ void __putback_isolated_page(struct page *page, unsigned int order, int mt)
 
 	/* Return isolated page to tail of freelist. */
 	__free_one_page(page, page_to_pfn(page), zone, order, mt,
-			FPI_SKIP_REPORT_NOTIFY);
+			FPI_SKIP_REPORT_NOTIFY | FPI_TO_TAIL);
 }
 
 /*
-- 
2.26.2


^ permalink raw reply	[flat|nested] 11+ messages in thread

* [PATCH v2 3/5] mm/page_alloc: move pages to tail in move_to_free_list()
  2020-10-05 12:15 [PATCH v2 0/5] mm: place pages to the freelist tail when onlining and undoing isolation David Hildenbrand
  2020-10-05 12:15 ` [PATCH v2 1/5] mm/page_alloc: convert "report" flag of __free_one_page() to a proper flag David Hildenbrand
  2020-10-05 12:15 ` [PATCH v2 2/5] mm/page_alloc: place pages to tail in __putback_isolated_page() David Hildenbrand
@ 2020-10-05 12:15 ` David Hildenbrand
  2020-10-06 12:12   ` Michal Hocko
  2020-10-20 17:20   ` Vlastimil Babka
  2020-10-05 12:15 ` [PATCH v2 4/5] mm/page_alloc: place pages to tail in __free_pages_core() David Hildenbrand
  2020-10-05 12:15 ` [PATCH v2 5/5] mm/memory_hotplug: update comment regarding zone shuffling David Hildenbrand
  4 siblings, 2 replies; 11+ messages in thread
From: David Hildenbrand @ 2020-10-05 12:15 UTC (permalink / raw)
  To: linux-kernel
  Cc: linux-mm, linux-hyperv, xen-devel, linux-acpi, Andrew Morton,
	Matthew Wilcox, David Hildenbrand, Oscar Salvador, Pankaj Gupta,
	Wei Yang, Alexander Duyck, Mel Gorman, Michal Hocko, Dave Hansen,
	Vlastimil Babka, Mike Rapoport, Scott Cheloha, Michael Ellerman

Whenever we move pages between freelists via move_to_free_list()/
move_freepages_block(), we don't actually touch the pages:
1. Page isolation doesn't actually touch the pages, it simply isolates
   pageblocks and moves all free pages to the MIGRATE_ISOLATE freelist.
   When undoing isolation, we move the pages back to the target list.
2. Page stealing (steal_suitable_fallback()) moves free pages directly
   between lists without touching them.
3. reserve_highatomic_pageblock()/unreserve_highatomic_pageblock() moves
   free pages directly between freelists without touching them.

We already place pages to the tail of the freelists when undoing isolation
via __putback_isolated_page(), let's do it in any case (e.g., if order <=
pageblock_order) and document the behavior. To simplify, let's move the
pages to the tail for all move_to_free_list()/move_freepages_block() users.

In 2., the target list is empty, so there should be no change. In 3.,
we might observe a change, however, highatomic is more concerned about
allocations succeeding than cache hotness - if we ever realize this
change degrades a workload, we can special-case this instance and add a
proper comment.

This change results in all pages getting onlined via online_pages() to
be placed to the tail of the freelist.

Reviewed-by: Oscar Salvador <osalvador@suse.de>
Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Reviewed-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Scott Cheloha <cheloha@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/page_alloc.c     | 10 +++++++---
 mm/page_isolation.c |  5 +++++
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index df5ff0cd6df1..b187e46cf640 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -901,13 +901,17 @@ static inline void add_to_free_list_tail(struct page *page, struct zone *zone,
 	area->nr_free++;
 }
 
-/* Used for pages which are on another list */
+/*
+ * Used for pages which are on another list. Move the pages to the tail
+ * of the list - so the moved pages won't immediately be considered for
+ * allocation again (e.g., optimization for memory onlining).
+ */
 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]);
+	list_move_tail(&page->lru, &area->free_list[migratetype]);
 }
 
 static inline void del_page_from_free_list(struct page *page, struct zone *zone,
@@ -2340,7 +2344,7 @@ static inline struct page *__rmqueue_cma_fallback(struct zone *zone,
 #endif
 
 /*
- * Move the free pages in a range to the free lists of the requested type.
+ * Move the free pages in a range to the freelist tail of the requested type.
  * Note that start_page and end_pages are not aligned on a pageblock
  * boundary. If alignment is required, use move_freepages_block()
  */
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index abfe26ad59fd..83692b937784 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -106,6 +106,11 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
 	 * If we isolate freepage with more than pageblock_order, there
 	 * should be no freepage in the range, so we could avoid costly
 	 * pageblock scanning for freepage moving.
+	 *
+	 * We didn't actually touch any of the isolated pages, so place them
+	 * to the tail of the freelist. This is an optimization for memory
+	 * onlining - just onlined memory won't immediately be considered for
+	 * allocation.
 	 */
 	if (!isolated_page) {
 		nr_pages = move_freepages_block(zone, page, migratetype, NULL);
-- 
2.26.2


^ permalink raw reply	[flat|nested] 11+ messages in thread

* [PATCH v2 4/5] mm/page_alloc: place pages to tail in __free_pages_core()
  2020-10-05 12:15 [PATCH v2 0/5] mm: place pages to the freelist tail when onlining and undoing isolation David Hildenbrand
                   ` (2 preceding siblings ...)
  2020-10-05 12:15 ` [PATCH v2 3/5] mm/page_alloc: move pages to tail in move_to_free_list() David Hildenbrand
@ 2020-10-05 12:15 ` David Hildenbrand
  2020-10-05 12:15 ` [PATCH v2 5/5] mm/memory_hotplug: update comment regarding zone shuffling David Hildenbrand
  4 siblings, 0 replies; 11+ messages in thread
From: David Hildenbrand @ 2020-10-05 12:15 UTC (permalink / raw)
  To: linux-kernel
  Cc: linux-mm, linux-hyperv, xen-devel, linux-acpi, Andrew Morton,
	Matthew Wilcox, David Hildenbrand, Vlastimil Babka,
	Oscar Salvador, Pankaj Gupta, Wei Yang, Michal Hocko,
	Alexander Duyck, Mel Gorman, Michal Hocko, Dave Hansen,
	Mike Rapoport, K. Y. Srinivasan, Haiyang Zhang,
	Stephen Hemminger, Wei Liu

__free_pages_core() is used when exposing fresh memory to the buddy
during system boot and when onlining memory in generic_online_page().

generic_online_page() is used in two cases:

1. Direct memory onlining in online_pages().
2. Deferred memory onlining in memory-ballooning-like mechanisms (HyperV
   balloon and virtio-mem), when parts of a section are kept
   fake-offline to be fake-onlined later on.

In 1, we already place pages to the tail of the freelist. Pages will be
freed to MIGRATE_ISOLATE lists first and moved to the tail of the freelists
via undo_isolate_page_range().

In 2, we currently don't implement a proper rule. In case of virtio-mem,
where we currently always online MAX_ORDER - 1 pages, the pages will be
placed to the HEAD of the freelist - undesireable. While the hyper-v
balloon calls generic_online_page() with single pages, usually it will
call it on successive single pages in a larger block.

The pages are fresh, so place them to the tail of the freelist and avoid
the PCP. In __free_pages_core(), remove the now superflouos call to
set_page_refcounted() and add a comment regarding page initialization and
the refcount.

Note: In 2. we currently don't shuffle. If ever relevant (page shuffling
is usually of limited use in virtualized environments), we might want to
shuffle after a sequence of generic_online_page() calls in the
relevant callers.

Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Reviewed-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: Wei Liu <wei.liu@kernel.org>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/page_alloc.c | 33 +++++++++++++++++++++++----------
 1 file changed, 23 insertions(+), 10 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b187e46cf640..3dadcc6d4009 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -275,7 +275,8 @@ bool pm_suspended_storage(void)
 unsigned int pageblock_order __read_mostly;
 #endif
 
-static void __free_pages_ok(struct page *page, unsigned int order);
+static void __free_pages_ok(struct page *page, unsigned int order,
+			    fpi_t fpi_flags);
 
 /*
  * results with 256, 32 in the lowmem_reserve sysctl:
@@ -687,7 +688,7 @@ static void bad_page(struct page *page, const char *reason)
 void free_compound_page(struct page *page)
 {
 	mem_cgroup_uncharge(page);
-	__free_pages_ok(page, compound_order(page));
+	__free_pages_ok(page, compound_order(page), FPI_NONE);
 }
 
 void prep_compound_page(struct page *page, unsigned int order)
@@ -1423,14 +1424,14 @@ static void free_pcppages_bulk(struct zone *zone, int count,
 static void free_one_page(struct zone *zone,
 				struct page *page, unsigned long pfn,
 				unsigned int order,
-				int migratetype)
+				int migratetype, fpi_t fpi_flags)
 {
 	spin_lock(&zone->lock);
 	if (unlikely(has_isolate_pageblock(zone) ||
 		is_migrate_isolate(migratetype))) {
 		migratetype = get_pfnblock_migratetype(page, pfn);
 	}
-	__free_one_page(page, pfn, zone, order, migratetype, FPI_NONE);
+	__free_one_page(page, pfn, zone, order, migratetype, fpi_flags);
 	spin_unlock(&zone->lock);
 }
 
@@ -1508,7 +1509,8 @@ void __meminit reserve_bootmem_region(phys_addr_t start, phys_addr_t end)
 	}
 }
 
-static void __free_pages_ok(struct page *page, unsigned int order)
+static void __free_pages_ok(struct page *page, unsigned int order,
+			    fpi_t fpi_flags)
 {
 	unsigned long flags;
 	int migratetype;
@@ -1520,7 +1522,8 @@ static void __free_pages_ok(struct page *page, unsigned int order)
 	migratetype = get_pfnblock_migratetype(page, pfn);
 	local_irq_save(flags);
 	__count_vm_events(PGFREE, 1 << order);
-	free_one_page(page_zone(page), page, pfn, order, migratetype);
+	free_one_page(page_zone(page), page, pfn, order, migratetype,
+		      fpi_flags);
 	local_irq_restore(flags);
 }
 
@@ -1530,6 +1533,11 @@ void __free_pages_core(struct page *page, unsigned int order)
 	struct page *p = page;
 	unsigned int loop;
 
+	/*
+	 * When initializing the memmap, __init_single_page() sets the refcount
+	 * of all pages to 1 ("allocated"/"not free"). We have to set the
+	 * refcount of all involved pages to 0.
+	 */
 	prefetchw(p);
 	for (loop = 0; loop < (nr_pages - 1); loop++, p++) {
 		prefetchw(p + 1);
@@ -1540,8 +1548,12 @@ void __free_pages_core(struct page *page, unsigned int order)
 	set_page_count(p, 0);
 
 	atomic_long_add(nr_pages, &page_zone(page)->managed_pages);
-	set_page_refcounted(page);
-	__free_pages(page, order);
+
+	/*
+	 * Bypass PCP and place fresh pages right to the tail, primarily
+	 * relevant for memory onlining.
+	 */
+	__free_pages_ok(page, order, FPI_TO_TAIL);
 }
 
 #ifdef CONFIG_NEED_MULTIPLE_NODES
@@ -3168,7 +3180,8 @@ static void free_unref_page_commit(struct page *page, unsigned long pfn)
 	 */
 	if (migratetype >= MIGRATE_PCPTYPES) {
 		if (unlikely(is_migrate_isolate(migratetype))) {
-			free_one_page(zone, page, pfn, 0, migratetype);
+			free_one_page(zone, page, pfn, 0, migratetype,
+				      FPI_NONE);
 			return;
 		}
 		migratetype = MIGRATE_MOVABLE;
@@ -4991,7 +5004,7 @@ static inline void free_the_page(struct page *page, unsigned int order)
 	if (order == 0)		/* Via pcp? */
 		free_unref_page(page);
 	else
-		__free_pages_ok(page, order);
+		__free_pages_ok(page, order, FPI_NONE);
 }
 
 void __free_pages(struct page *page, unsigned int order)
-- 
2.26.2


^ permalink raw reply	[flat|nested] 11+ messages in thread

* [PATCH v2 5/5] mm/memory_hotplug: update comment regarding zone shuffling
  2020-10-05 12:15 [PATCH v2 0/5] mm: place pages to the freelist tail when onlining and undoing isolation David Hildenbrand
                   ` (3 preceding siblings ...)
  2020-10-05 12:15 ` [PATCH v2 4/5] mm/page_alloc: place pages to tail in __free_pages_core() David Hildenbrand
@ 2020-10-05 12:15 ` David Hildenbrand
  2020-10-20 17:21   ` Vlastimil Babka
  2020-10-21 10:58   ` Pankaj Gupta
  4 siblings, 2 replies; 11+ messages in thread
From: David Hildenbrand @ 2020-10-05 12:15 UTC (permalink / raw)
  To: linux-kernel
  Cc: linux-mm, linux-hyperv, xen-devel, linux-acpi, Andrew Morton,
	Matthew Wilcox, David Hildenbrand, Wei Yang, Michal Hocko,
	Alexander Duyck, Mel Gorman, Michal Hocko, Dave Hansen,
	Vlastimil Babka, Oscar Salvador, Mike Rapoport, Pankaj Gupta

As we no longer shuffle via generic_online_page() and when undoing
isolation, we can simplify the comment.

We now effectively shuffle only once (properly) when onlining new
memory.

Reviewed-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/memory_hotplug.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 03a00cb68bf7..b44d4c7ba73b 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -858,13 +858,10 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
 	undo_isolate_page_range(pfn, pfn + nr_pages, MIGRATE_MOVABLE);
 
 	/*
-	 * When exposing larger, physically contiguous memory areas to the
-	 * buddy, shuffling in the buddy (when freeing onlined pages, putting
-	 * them either to the head or the tail of the freelist) is only helpful
-	 * for maintaining the shuffle, but not for creating the initial
-	 * shuffle. Shuffle the whole zone to make sure the just onlined pages
-	 * are properly distributed across the whole freelist. Make sure to
-	 * shuffle once pageblocks are no longer isolated.
+	 * Freshly onlined pages aren't shuffled (e.g., all pages are placed to
+	 * the tail of the freelist when undoing isolation). Shuffle the whole
+	 * zone to make sure the just onlined pages are properly distributed
+	 * across the whole freelist - to create an initial shuffle.
 	 */
 	shuffle_zone(zone);
 
-- 
2.26.2


^ permalink raw reply	[flat|nested] 11+ messages in thread

* Re: [PATCH v2 3/5] mm/page_alloc: move pages to tail in move_to_free_list()
  2020-10-05 12:15 ` [PATCH v2 3/5] mm/page_alloc: move pages to tail in move_to_free_list() David Hildenbrand
@ 2020-10-06 12:12   ` Michal Hocko
  2020-10-20 17:20   ` Vlastimil Babka
  1 sibling, 0 replies; 11+ messages in thread
From: Michal Hocko @ 2020-10-06 12:12 UTC (permalink / raw)
  To: David Hildenbrand
  Cc: linux-kernel, linux-mm, linux-hyperv, xen-devel, linux-acpi,
	Andrew Morton, Matthew Wilcox, Oscar Salvador, Pankaj Gupta,
	Wei Yang, Alexander Duyck, Mel Gorman, Dave Hansen,
	Vlastimil Babka, Mike Rapoport, Scott Cheloha, Michael Ellerman

On Mon 05-10-20 14:15:32, David Hildenbrand wrote:
> Whenever we move pages between freelists via move_to_free_list()/
> move_freepages_block(), we don't actually touch the pages:
> 1. Page isolation doesn't actually touch the pages, it simply isolates
>    pageblocks and moves all free pages to the MIGRATE_ISOLATE freelist.
>    When undoing isolation, we move the pages back to the target list.
> 2. Page stealing (steal_suitable_fallback()) moves free pages directly
>    between lists without touching them.
> 3. reserve_highatomic_pageblock()/unreserve_highatomic_pageblock() moves
>    free pages directly between freelists without touching them.
> 
> We already place pages to the tail of the freelists when undoing isolation
> via __putback_isolated_page(), let's do it in any case (e.g., if order <=
> pageblock_order) and document the behavior. To simplify, let's move the
> pages to the tail for all move_to_free_list()/move_freepages_block() users.
> 
> In 2., the target list is empty, so there should be no change. In 3.,
> we might observe a change, however, highatomic is more concerned about
> allocations succeeding than cache hotness - if we ever realize this
> change degrades a workload, we can special-case this instance and add a
> proper comment.
> 
> This change results in all pages getting onlined via online_pages() to
> be placed to the tail of the freelist.
> 
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
> Reviewed-by: Wei Yang <richard.weiyang@linux.alibaba.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Dave Hansen <dave.hansen@intel.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Mike Rapoport <rppt@kernel.org>
> Cc: Scott Cheloha <cheloha@linux.ibm.com>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Much simpler!
Acked-by: Michal Hocko <mhocko@suse.com>

Thanks!

> ---
>  mm/page_alloc.c     | 10 +++++++---
>  mm/page_isolation.c |  5 +++++
>  2 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index df5ff0cd6df1..b187e46cf640 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -901,13 +901,17 @@ static inline void add_to_free_list_tail(struct page *page, struct zone *zone,
>  	area->nr_free++;
>  }
>  
> -/* Used for pages which are on another list */
> +/*
> + * Used for pages which are on another list. Move the pages to the tail
> + * of the list - so the moved pages won't immediately be considered for
> + * allocation again (e.g., optimization for memory onlining).
> + */
>  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]);
> +	list_move_tail(&page->lru, &area->free_list[migratetype]);
>  }
>  
>  static inline void del_page_from_free_list(struct page *page, struct zone *zone,
> @@ -2340,7 +2344,7 @@ static inline struct page *__rmqueue_cma_fallback(struct zone *zone,
>  #endif
>  
>  /*
> - * Move the free pages in a range to the free lists of the requested type.
> + * Move the free pages in a range to the freelist tail of the requested type.
>   * Note that start_page and end_pages are not aligned on a pageblock
>   * boundary. If alignment is required, use move_freepages_block()
>   */
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index abfe26ad59fd..83692b937784 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -106,6 +106,11 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
>  	 * If we isolate freepage with more than pageblock_order, there
>  	 * should be no freepage in the range, so we could avoid costly
>  	 * pageblock scanning for freepage moving.
> +	 *
> +	 * We didn't actually touch any of the isolated pages, so place them
> +	 * to the tail of the freelist. This is an optimization for memory
> +	 * onlining - just onlined memory won't immediately be considered for
> +	 * allocation.
>  	 */
>  	if (!isolated_page) {
>  		nr_pages = move_freepages_block(zone, page, migratetype, NULL);
> -- 
> 2.26.2

-- 
Michal Hocko
SUSE Labs

^ permalink raw reply	[flat|nested] 11+ messages in thread

* Re: [PATCH v2 2/5] mm/page_alloc: place pages to tail in __putback_isolated_page()
  2020-10-05 12:15 ` [PATCH v2 2/5] mm/page_alloc: place pages to tail in __putback_isolated_page() David Hildenbrand
@ 2020-10-20 17:18   ` Vlastimil Babka
  0 siblings, 0 replies; 11+ messages in thread
From: Vlastimil Babka @ 2020-10-20 17:18 UTC (permalink / raw)
  To: David Hildenbrand, linux-kernel
  Cc: linux-mm, linux-hyperv, xen-devel, linux-acpi, Andrew Morton,
	Matthew Wilcox, Alexander Duyck, Oscar Salvador, Wei Yang,
	Pankaj Gupta, Michal Hocko, Mel Gorman, Michal Hocko,
	Dave Hansen, Mike Rapoport, Scott Cheloha, Michael Ellerman

On 10/5/20 2:15 PM, David Hildenbrand wrote:
> __putback_isolated_page() already documents that pages will be placed to
> the tail of the freelist - this is, however, not the case for
> "order >= MAX_ORDER - 2" (see buddy_merge_likely()) - which should be
> the case for all existing users.
> 
> This change affects two users:
> - free page reporting
> - page isolation, when undoing the isolation (including memory onlining).
> 
> This behavior is desireable for pages that haven't really been touched
> lately, so exactly the two users that don't actually read/write page
> content, but rather move untouched pages.
> 
> The new behavior is especially desirable for memory onlining, where we
> allow allocation of newly onlined pages via undo_isolate_page_range()
> in online_pages(). Right now, we always place them to the head of the
> freelist, resulting in undesireable behavior: Assume we add
> individual memory chunks via add_memory() and online them right away to
> the NORMAL zone. We create a dependency chain of unmovable allocations
> e.g., via the memmap. The memmap of the next chunk will be placed onto
> previous chunks - if the last block cannot get offlined+removed, all
> dependent ones cannot get offlined+removed. While this can already be
> observed with individual DIMMs, it's more of an issue for virtio-mem
> (and I suspect also ppc DLPAR).
> 
> Document that this should only be used for optimizations, and no code
> should rely on this behavior for correction (if the order of the
> freelists ever changes).
> 
> We won't care about page shuffling: memory onlining already properly
> shuffles after onlining. free page reporting doesn't care about
> physically contiguous ranges, and there are already cases where page
> isolation will simply move (physically close) free pages to (currently)
> the head of the freelists via move_freepages_block() instead of
> shuffling. If this becomes ever relevant, we should shuffle the whole
> zone when undoing isolation of larger ranges, and after
> free_contig_range().
> 
> Reviewed-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> Reviewed-by: Wei Yang <richard.weiyang@linux.alibaba.com>
> Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
> Acked-by: Michal Hocko <mhocko@suse.com>

Reviewed-by: Vlastimil Babka <vbabka@suse.cz>

^ permalink raw reply	[flat|nested] 11+ messages in thread

* Re: [PATCH v2 3/5] mm/page_alloc: move pages to tail in move_to_free_list()
  2020-10-05 12:15 ` [PATCH v2 3/5] mm/page_alloc: move pages to tail in move_to_free_list() David Hildenbrand
  2020-10-06 12:12   ` Michal Hocko
@ 2020-10-20 17:20   ` Vlastimil Babka
  1 sibling, 0 replies; 11+ messages in thread
From: Vlastimil Babka @ 2020-10-20 17:20 UTC (permalink / raw)
  To: David Hildenbrand, linux-kernel
  Cc: linux-mm, linux-hyperv, xen-devel, linux-acpi, Andrew Morton,
	Matthew Wilcox, Oscar Salvador, Pankaj Gupta, Wei Yang,
	Alexander Duyck, Mel Gorman, Michal Hocko, Dave Hansen,
	Mike Rapoport, Scott Cheloha, Michael Ellerman

On 10/5/20 2:15 PM, David Hildenbrand wrote:
> Whenever we move pages between freelists via move_to_free_list()/
> move_freepages_block(), we don't actually touch the pages:
> 1. Page isolation doesn't actually touch the pages, it simply isolates
>     pageblocks and moves all free pages to the MIGRATE_ISOLATE freelist.
>     When undoing isolation, we move the pages back to the target list.
> 2. Page stealing (steal_suitable_fallback()) moves free pages directly
>     between lists without touching them.
> 3. reserve_highatomic_pageblock()/unreserve_highatomic_pageblock() moves
>     free pages directly between freelists without touching them.
> 
> We already place pages to the tail of the freelists when undoing isolation
> via __putback_isolated_page(), let's do it in any case (e.g., if order <=
> pageblock_order) and document the behavior. To simplify, let's move the
> pages to the tail for all move_to_free_list()/move_freepages_block() users.
> 
> In 2., the target list is empty, so there should be no change. In 3.,
> we might observe a change, however, highatomic is more concerned about
> allocations succeeding than cache hotness - if we ever realize this
> change degrades a workload, we can special-case this instance and add a
> proper comment.
> 
> This change results in all pages getting onlined via online_pages() to
> be placed to the tail of the freelist.
> 
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
> Reviewed-by: Wei Yang <richard.weiyang@linux.alibaba.com>

Reviewed-by: Vlastimil Babka <vbabka@suse.cz>

^ permalink raw reply	[flat|nested] 11+ messages in thread

* Re: [PATCH v2 5/5] mm/memory_hotplug: update comment regarding zone shuffling
  2020-10-05 12:15 ` [PATCH v2 5/5] mm/memory_hotplug: update comment regarding zone shuffling David Hildenbrand
@ 2020-10-20 17:21   ` Vlastimil Babka
  2020-10-21 10:58   ` Pankaj Gupta
  1 sibling, 0 replies; 11+ messages in thread
From: Vlastimil Babka @ 2020-10-20 17:21 UTC (permalink / raw)
  To: David Hildenbrand, linux-kernel
  Cc: linux-mm, linux-hyperv, xen-devel, linux-acpi, Andrew Morton,
	Matthew Wilcox, Wei Yang, Michal Hocko, Alexander Duyck,
	Mel Gorman, Michal Hocko, Dave Hansen, Oscar Salvador,
	Mike Rapoport, Pankaj Gupta

On 10/5/20 2:15 PM, David Hildenbrand wrote:
> As we no longer shuffle via generic_online_page() and when undoing
> isolation, we can simplify the comment.
> 
> We now effectively shuffle only once (properly) when onlining new
> memory.
> 
> Reviewed-by: Wei Yang <richard.weiyang@linux.alibaba.com>
> Acked-by: Michal Hocko <mhocko@suse.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Dave Hansen <dave.hansen@intel.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Mike Rapoport <rppt@kernel.org>
> Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>   mm/memory_hotplug.c | 11 ++++-------
>   1 file changed, 4 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 03a00cb68bf7..b44d4c7ba73b 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -858,13 +858,10 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
>   	undo_isolate_page_range(pfn, pfn + nr_pages, MIGRATE_MOVABLE);
>   
>   	/*
> -	 * When exposing larger, physically contiguous memory areas to the
> -	 * buddy, shuffling in the buddy (when freeing onlined pages, putting
> -	 * them either to the head or the tail of the freelist) is only helpful
> -	 * for maintaining the shuffle, but not for creating the initial
> -	 * shuffle. Shuffle the whole zone to make sure the just onlined pages
> -	 * are properly distributed across the whole freelist. Make sure to
> -	 * shuffle once pageblocks are no longer isolated.
> +	 * Freshly onlined pages aren't shuffled (e.g., all pages are placed to
> +	 * the tail of the freelist when undoing isolation). Shuffle the whole
> +	 * zone to make sure the just onlined pages are properly distributed
> +	 * across the whole freelist - to create an initial shuffle.
>   	 */
>   	shuffle_zone(zone);
>   
> 


^ permalink raw reply	[flat|nested] 11+ messages in thread

* Re: [PATCH v2 5/5] mm/memory_hotplug: update comment regarding zone shuffling
  2020-10-05 12:15 ` [PATCH v2 5/5] mm/memory_hotplug: update comment regarding zone shuffling David Hildenbrand
  2020-10-20 17:21   ` Vlastimil Babka
@ 2020-10-21 10:58   ` Pankaj Gupta
  1 sibling, 0 replies; 11+ messages in thread
From: Pankaj Gupta @ 2020-10-21 10:58 UTC (permalink / raw)
  To: David Hildenbrand
  Cc: LKML, Linux MM, linux-hyperv, xen-devel, linux-acpi,
	Andrew Morton, Matthew Wilcox, Wei Yang, Michal Hocko,
	Alexander Duyck, Mel Gorman, Michal Hocko, Dave Hansen,
	Vlastimil Babka, Oscar Salvador, Mike Rapoport

> As we no longer shuffle via generic_online_page() and when undoing
> isolation, we can simplify the comment.
>
> We now effectively shuffle only once (properly) when onlining new
> memory.
>
> Reviewed-by: Wei Yang <richard.weiyang@linux.alibaba.com>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Dave Hansen <dave.hansen@intel.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Mike Rapoport <rppt@kernel.org>
> Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  mm/memory_hotplug.c | 11 ++++-------
>  1 file changed, 4 insertions(+), 7 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 03a00cb68bf7..b44d4c7ba73b 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -858,13 +858,10 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
>         undo_isolate_page_range(pfn, pfn + nr_pages, MIGRATE_MOVABLE);
>
>         /*
> -        * When exposing larger, physically contiguous memory areas to the
> -        * buddy, shuffling in the buddy (when freeing onlined pages, putting
> -        * them either to the head or the tail of the freelist) is only helpful
> -        * for maintaining the shuffle, but not for creating the initial
> -        * shuffle. Shuffle the whole zone to make sure the just onlined pages
> -        * are properly distributed across the whole freelist. Make sure to
> -        * shuffle once pageblocks are no longer isolated.
> +        * Freshly onlined pages aren't shuffled (e.g., all pages are placed to
> +        * the tail of the freelist when undoing isolation). Shuffle the whole
> +        * zone to make sure the just onlined pages are properly distributed
> +        * across the whole freelist - to create an initial shuffle.
>          */
>         shuffle_zone(zone);
>

Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>

^ permalink raw reply	[flat|nested] 11+ messages in thread

end of thread, back to index

Thread overview: 11+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-10-05 12:15 [PATCH v2 0/5] mm: place pages to the freelist tail when onlining and undoing isolation David Hildenbrand
2020-10-05 12:15 ` [PATCH v2 1/5] mm/page_alloc: convert "report" flag of __free_one_page() to a proper flag David Hildenbrand
2020-10-05 12:15 ` [PATCH v2 2/5] mm/page_alloc: place pages to tail in __putback_isolated_page() David Hildenbrand
2020-10-20 17:18   ` Vlastimil Babka
2020-10-05 12:15 ` [PATCH v2 3/5] mm/page_alloc: move pages to tail in move_to_free_list() David Hildenbrand
2020-10-06 12:12   ` Michal Hocko
2020-10-20 17:20   ` Vlastimil Babka
2020-10-05 12:15 ` [PATCH v2 4/5] mm/page_alloc: place pages to tail in __free_pages_core() David Hildenbrand
2020-10-05 12:15 ` [PATCH v2 5/5] mm/memory_hotplug: update comment regarding zone shuffling David Hildenbrand
2020-10-20 17:21   ` Vlastimil Babka
2020-10-21 10:58   ` Pankaj Gupta

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