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From: Mel Gorman <mgorman@suse.de>
To: David Rientjes <rientjes@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Rik van Riel <riel@redhat.com>, Vlastimil Babka <vbabka@suse.cz>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Greg Thelen <gthelen@google.com>, Hugh Dickins <hughd@google.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [patch v2 4/4] mm, thp: do not perform sync compaction on pagefault
Date: Fri, 2 May 2014 11:22:31 +0100	[thread overview]
Message-ID: <20140502102231.GQ23991@suse.de> (raw)
In-Reply-To: <alpine.DEB.2.02.1405011435210.23898@chino.kir.corp.google.com>

On Thu, May 01, 2014 at 02:35:48PM -0700, David Rientjes wrote:
> Synchronous memory compaction can be very expensive: it can iterate an enormous 
> amount of memory without aborting, constantly rescheduling, waiting on page
> locks and lru_lock, etc, if a pageblock cannot be defragmented.
> 
> Unfortunately, it's too expensive for pagefault for transparent hugepages and 
> it's much better to simply fallback to pages.  On 128GB machines, we find that 
> synchronous memory compaction can take O(seconds) for a single thp fault.
> 
> Now that async compaction remembers where it left off without strictly relying
> on sync compaction, this makes thp allocations best-effort without causing
> egregious latency during pagefault.
> 
> Signed-off-by: David Rientjes <rientjes@google.com>

Compaction uses MIGRATE_SYNC_LIGHT which in the current implementation
avoids calling ->writepage to clean dirty page in the fallback migrate
case

static int fallback_migrate_page(struct address_space *mapping,
        struct page *newpage, struct page *page, enum migrate_mode mode)
{
        if (PageDirty(page)) {
                /* Only writeback pages in full synchronous migration */
                if (mode != MIGRATE_SYNC)
                        return -EBUSY;
                return writeout(mapping, page);
        }

or waiting on page writeback in other cases

                /*
                 * Only in the case of a full synchronous migration is it
                 * necessary to wait for PageWriteback. In the async case,
                 * the retry loop is too short and in the sync-light case,
                 * the overhead of stalling is too much
                 */
                if (mode != MIGRATE_SYNC) {
                        rc = -EBUSY;
                        goto uncharge;
                }

or on acquiring the page lock for unforced migrations.

However, buffers still get locked in the SYNC_LIGHT case causing stalls
in buffer_migrate_lock_buffers which may be undesirable or maybe you are
hitting some other case. It would be preferable to identify what is
getting stalled in SYNC_LIGHT compaction and fix that rather than
disabling it entirely. You may also want to distinguish between a direct
compaction by a process and collapsing huge pages as done by khugepaged.

-- 
Mel Gorman
SUSE Labs

WARNING: multiple messages have this Message-ID (diff)
From: Mel Gorman <mgorman@suse.de>
To: David Rientjes <rientjes@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Rik van Riel <riel@redhat.com>, Vlastimil Babka <vbabka@suse.cz>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Greg Thelen <gthelen@google.com>, Hugh Dickins <hughd@google.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [patch v2 4/4] mm, thp: do not perform sync compaction on pagefault
Date: Fri, 2 May 2014 11:22:31 +0100	[thread overview]
Message-ID: <20140502102231.GQ23991@suse.de> (raw)
In-Reply-To: <alpine.DEB.2.02.1405011435210.23898@chino.kir.corp.google.com>

On Thu, May 01, 2014 at 02:35:48PM -0700, David Rientjes wrote:
> Synchronous memory compaction can be very expensive: it can iterate an enormous 
> amount of memory without aborting, constantly rescheduling, waiting on page
> locks and lru_lock, etc, if a pageblock cannot be defragmented.
> 
> Unfortunately, it's too expensive for pagefault for transparent hugepages and 
> it's much better to simply fallback to pages.  On 128GB machines, we find that 
> synchronous memory compaction can take O(seconds) for a single thp fault.
> 
> Now that async compaction remembers where it left off without strictly relying
> on sync compaction, this makes thp allocations best-effort without causing
> egregious latency during pagefault.
> 
> Signed-off-by: David Rientjes <rientjes@google.com>

Compaction uses MIGRATE_SYNC_LIGHT which in the current implementation
avoids calling ->writepage to clean dirty page in the fallback migrate
case

static int fallback_migrate_page(struct address_space *mapping,
        struct page *newpage, struct page *page, enum migrate_mode mode)
{
        if (PageDirty(page)) {
                /* Only writeback pages in full synchronous migration */
                if (mode != MIGRATE_SYNC)
                        return -EBUSY;
                return writeout(mapping, page);
        }

or waiting on page writeback in other cases

                /*
                 * Only in the case of a full synchronous migration is it
                 * necessary to wait for PageWriteback. In the async case,
                 * the retry loop is too short and in the sync-light case,
                 * the overhead of stalling is too much
                 */
                if (mode != MIGRATE_SYNC) {
                        rc = -EBUSY;
                        goto uncharge;
                }

or on acquiring the page lock for unforced migrations.

However, buffers still get locked in the SYNC_LIGHT case causing stalls
in buffer_migrate_lock_buffers which may be undesirable or maybe you are
hitting some other case. It would be preferable to identify what is
getting stalled in SYNC_LIGHT compaction and fix that rather than
disabling it entirely. You may also want to distinguish between a direct
compaction by a process and collapsing huge pages as done by khugepaged.

-- 
Mel Gorman
SUSE Labs

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  reply	other threads:[~2014-05-02 10:22 UTC|newest]

Thread overview: 267+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-05-01  0:45 [patch 1/2] mm, migration: add destination page freeing callback David Rientjes
2014-05-01  0:45 ` David Rientjes
2014-05-01  0:45 ` [patch 2/2] mm, compaction: return failed migration target pages back to freelist David Rientjes
2014-05-01  0:45   ` David Rientjes
2014-05-01  5:10   ` Naoya Horiguchi
2014-05-01 21:02     ` David Rientjes
2014-05-01 21:02       ` David Rientjes
2014-05-01  5:08 ` [patch 1/2] mm, migration: add destination page freeing callback Naoya Horiguchi
     [not found] ` <5361d71e.236ec20a.1b3d.ffffc8aeSMTPIN_ADDED_BROKEN@mx.google.com>
2014-05-01 21:02   ` David Rientjes
2014-05-01 21:02     ` David Rientjes
2014-05-01 21:35 ` [patch v2 1/4] " David Rientjes
2014-05-01 21:35   ` David Rientjes
2014-05-01 21:35   ` [patch v2 2/4] mm, compaction: return failed migration target pages back to freelist David Rientjes
2014-05-01 21:35     ` David Rientjes
2014-05-02 10:11     ` Mel Gorman
2014-05-02 10:11       ` Mel Gorman
2014-05-02 15:23     ` Vlastimil Babka
2014-05-02 15:23       ` Vlastimil Babka
2014-05-02 15:26       ` [PATCH] mm/compaction: do not count migratepages when unnecessary Vlastimil Babka
2014-05-06 21:18         ` Naoya Horiguchi
     [not found]         ` <1399411134-k43fsr0p@n-horiguchi@ah.jp.nec.com>
2014-05-07  9:33           ` Vlastimil Babka
2014-05-07  9:33             ` Vlastimil Babka
2014-05-02 15:27       ` [PATCH 2/2] mm/compaction: avoid rescanning pageblocks in isolate_freepages Vlastimil Babka
2014-05-02 15:27         ` Vlastimil Babka
2014-05-06 22:19         ` Naoya Horiguchi
     [not found]         ` <1399414778-xakujfb3@n-horiguchi@ah.jp.nec.com>
2014-05-07  9:22           ` Vlastimil Babka
2014-05-07  9:22             ` Vlastimil Babka
2014-05-02 15:29       ` [PATCH 1/2] mm/compaction: do not count migratepages when unnecessary Vlastimil Babka
2014-05-02 15:29         ` Vlastimil Babka
2014-05-01 21:35   ` [patch v2 3/4] mm, compaction: add per-zone migration pfn cache for async compaction David Rientjes
2014-05-01 21:35     ` David Rientjes
2014-05-05  9:34     ` Vlastimil Babka
2014-05-05  9:34       ` Vlastimil Babka
2014-05-05  9:51       ` David Rientjes
2014-05-05  9:51         ` David Rientjes
2014-05-05 14:24         ` Vlastimil Babka
2014-05-05 14:24           ` Vlastimil Babka
2014-05-06  0:29           ` David Rientjes
2014-05-06  0:29             ` David Rientjes
2014-05-06 11:52             ` Vlastimil Babka
2014-05-06 11:52               ` Vlastimil Babka
2014-05-01 21:35   ` [patch v2 4/4] mm, thp: do not perform sync compaction on pagefault David Rientjes
2014-05-01 21:35     ` David Rientjes
2014-05-02 10:22     ` Mel Gorman [this message]
2014-05-02 10:22       ` Mel Gorman
2014-05-02 11:22       ` David Rientjes
2014-05-02 11:22         ` David Rientjes
2014-05-02 11:58         ` Mel Gorman
2014-05-02 20:29           ` David Rientjes
2014-05-02 20:29             ` David Rientjes
2014-05-05 14:48             ` Vlastimil Babka
2014-05-05 14:48               ` Vlastimil Babka
2014-05-06  8:55             ` Mel Gorman
2014-05-06  8:55               ` Mel Gorman
2014-05-06 15:05               ` Vlastimil Babka
2014-05-06 15:05                 ` Vlastimil Babka
2014-05-02 10:10   ` [patch v2 1/4] mm, migration: add destination page freeing callback Mel Gorman
2014-05-07  2:22   ` [patch v3 1/6] " David Rientjes
2014-05-07  2:22     ` David Rientjes
2014-05-07  2:22     ` [patch v3 2/6] mm, compaction: return failed migration target pages back to freelist David Rientjes
2014-05-07  2:22       ` David Rientjes
2014-05-07 14:14       ` Naoya Horiguchi
2014-05-07 21:15       ` Andrew Morton
2014-05-07 21:15         ` Andrew Morton
2014-05-07 21:21         ` David Rientjes
2014-05-07 21:21           ` David Rientjes
2014-05-12  8:35           ` Vlastimil Babka
2014-05-12  8:35             ` Vlastimil Babka
2014-05-07 21:39         ` Greg Thelen
2014-05-07 21:39           ` Greg Thelen
2014-05-12  8:37           ` Vlastimil Babka
2014-05-12  8:37             ` Vlastimil Babka
2014-05-07  2:22     ` [patch v3 3/6] mm, compaction: add per-zone migration pfn cache for async compaction David Rientjes
2014-05-07  2:22       ` David Rientjes
2014-05-07  9:34       ` Vlastimil Babka
2014-05-07  9:34         ` Vlastimil Babka
2014-05-07 20:56       ` Naoya Horiguchi
2014-05-07  2:22     ` [patch v3 4/6] mm, compaction: embed migration mode in compact_control David Rientjes
2014-05-07  2:22       ` David Rientjes
2014-05-07  9:55       ` Vlastimil Babka
2014-05-07  9:55         ` Vlastimil Babka
2014-05-07 10:36         ` [patch v4 " David Rientjes
2014-05-07 10:36           ` David Rientjes
2014-05-09 22:03           ` Andrew Morton
2014-05-09 22:03             ` Andrew Morton
2014-05-07  2:22     ` [patch v3 5/6] mm, thp: avoid excessive compaction latency during fault David Rientjes
2014-05-07  2:22       ` David Rientjes
2014-05-07  9:39       ` Mel Gorman
2014-05-07  9:39         ` Mel Gorman
2014-05-08  5:30       ` [patch -mm] mm, thp: avoid excessive compaction latency during fault fix David Rientjes
2014-05-08  5:30         ` David Rientjes
2014-05-13 10:00         ` Vlastimil Babka
2014-05-13 10:00           ` Vlastimil Babka
2014-05-22  2:49           ` David Rientjes
2014-05-22  2:49             ` David Rientjes
2014-05-22  8:43             ` Vlastimil Babka
2014-05-22  8:43               ` Vlastimil Babka
2014-05-07  2:22     ` [patch v3 6/6] mm, compaction: terminate async compaction when rescheduling David Rientjes
2014-05-07  2:22       ` David Rientjes
2014-05-07  9:41       ` Mel Gorman
2014-05-07  9:41         ` Mel Gorman
2014-05-07 12:09       ` [PATCH v2 1/2] mm/compaction: do not count migratepages when unnecessary Vlastimil Babka
2014-05-07 12:09         ` Vlastimil Babka
2014-05-07 12:09         ` [PATCH v2 2/2] mm/compaction: avoid rescanning pageblocks in isolate_freepages Vlastimil Babka
2014-05-07 12:09           ` Vlastimil Babka
2014-05-07 21:47           ` David Rientjes
2014-05-07 21:47             ` David Rientjes
2014-05-07 22:06           ` Naoya Horiguchi
2014-05-08  5:28           ` Joonsoo Kim
2014-05-08  5:28             ` Joonsoo Kim
2014-05-12  9:09             ` Vlastimil Babka
2014-05-12  9:09               ` Vlastimil Babka
2014-05-13  1:15               ` Joonsoo Kim
2014-05-13  1:15                 ` Joonsoo Kim
2014-05-09 15:49           ` Michal Nazarewicz
2014-05-09 15:49             ` Michal Nazarewicz
2014-05-19 10:14           ` Vlastimil Babka
2014-05-19 10:14             ` Vlastimil Babka
2014-05-22  2:51             ` David Rientjes
2014-05-22  2:51               ` David Rientjes
2014-05-07 21:44         ` [PATCH v2 1/2] mm/compaction: do not count migratepages when unnecessary David Rientjes
2014-05-07 21:44           ` David Rientjes
2014-05-09 15:48         ` Michal Nazarewicz
2014-05-09 15:48           ` Michal Nazarewicz
2014-05-12  9:51           ` Vlastimil Babka
2014-05-12  9:51             ` Vlastimil Babka
2014-05-07 12:10       ` [patch v3 6/6] mm, compaction: terminate async compaction when rescheduling Vlastimil Babka
2014-05-07 12:10         ` Vlastimil Babka
2014-05-07 21:20       ` Andrew Morton
2014-05-07 21:20         ` Andrew Morton
2014-05-07 21:28         ` David Rientjes
2014-05-07 21:28           ` David Rientjes
2014-05-08  5:17       ` Joonsoo Kim
2014-05-08  5:17         ` Joonsoo Kim
2014-05-12 14:15         ` [PATCH] mm, compaction: properly signal and act upon lock and need_sched() contention Vlastimil Babka
2014-05-12 14:15           ` Vlastimil Babka
2014-05-12 15:34           ` Naoya Horiguchi
     [not found]           ` <1399908847-ouuxeneo@n-horiguchi@ah.jp.nec.com>
2014-05-12 15:45             ` Vlastimil Babka
2014-05-12 15:45               ` Vlastimil Babka
2014-05-12 15:53               ` Naoya Horiguchi
2014-05-12 20:28           ` David Rientjes
2014-05-12 20:28             ` David Rientjes
2014-05-13  8:50             ` Vlastimil Babka
2014-05-13  8:50               ` Vlastimil Babka
2014-05-13  0:44           ` Joonsoo Kim
2014-05-13  0:44             ` Joonsoo Kim
2014-05-13  8:54             ` Vlastimil Babka
2014-05-13  8:54               ` Vlastimil Babka
2014-05-15  2:21               ` Joonsoo Kim
2014-05-15  2:21                 ` Joonsoo Kim
2014-05-16  9:47           ` [PATCH v2] " Vlastimil Babka
2014-05-16  9:47             ` Vlastimil Babka
2014-05-16 17:33             ` Michal Nazarewicz
2014-05-16 17:33               ` Michal Nazarewicz
2014-05-19 23:37             ` Andrew Morton
2014-05-19 23:37               ` Andrew Morton
2014-05-21 14:13               ` Vlastimil Babka
2014-05-21 14:13                 ` Vlastimil Babka
2014-05-21 20:11                 ` Andrew Morton
2014-05-21 20:11                   ` Andrew Morton
2014-05-22  3:20             ` compaction is still too expensive for thp (was: [PATCH v2] mm, compaction: properly signal and act upon lock and need_sched() contention) David Rientjes
2014-05-22  3:20               ` David Rientjes
2014-05-22  8:10               ` compaction is still too expensive for thp Vlastimil Babka
2014-05-22  8:10                 ` Vlastimil Babka
2014-05-22  8:55                 ` David Rientjes
2014-05-22  8:55                   ` David Rientjes
2014-05-22 12:03                   ` Vlastimil Babka
2014-05-22 12:03                     ` Vlastimil Babka
2014-06-04  0:29                     ` [patch -mm 1/3] mm: rename allocflags_to_migratetype for clarity David Rientjes
2014-06-04  0:29                       ` David Rientjes
2014-06-04  0:29                       ` [patch -mm 2/3] mm, compaction: pass gfp mask to compact_control David Rientjes
2014-06-04  0:29                         ` David Rientjes
2014-06-04  0:30                       ` [patch -mm 3/3] mm, compaction: avoid compacting memory for thp if pageblock cannot become free David Rientjes
2014-06-04  0:30                         ` David Rientjes
2014-06-04 11:04                         ` Mel Gorman
2014-06-04 11:04                           ` Mel Gorman
2014-06-04 22:02                           ` David Rientjes
2014-06-04 22:02                             ` David Rientjes
2014-06-04 16:07                         ` Vlastimil Babka
2014-06-04 16:07                           ` Vlastimil Babka
2014-06-04 16:11               ` [RFC PATCH 1/6] mm, compaction: periodically drop lock and restore IRQs in scanners Vlastimil Babka
2014-06-04 16:11                 ` Vlastimil Babka
2014-06-04 16:11                 ` [RFC PATCH 2/6] mm, compaction: skip rechecks when lock was already held Vlastimil Babka
2014-06-04 16:11                   ` Vlastimil Babka
2014-06-04 23:46                   ` David Rientjes
2014-06-04 23:46                     ` David Rientjes
2014-06-04 16:11                 ` [RFC PATCH 3/6] mm, compaction: remember position within pageblock in free pages scanner Vlastimil Babka
2014-06-04 16:11                   ` Vlastimil Babka
2014-06-04 16:11                 ` [RFC PATCH 4/6] mm, compaction: skip buddy pages by their order in the migrate scanner Vlastimil Babka
2014-06-04 16:11                   ` Vlastimil Babka
2014-06-05  0:02                   ` David Rientjes
2014-06-05  0:02                     ` David Rientjes
2014-06-05  9:24                     ` Vlastimil Babka
2014-06-05  9:24                       ` Vlastimil Babka
2014-06-05 21:30                       ` David Rientjes
2014-06-05 21:30                         ` David Rientjes
2014-06-06  7:20                         ` Vlastimil Babka
2014-06-06  7:20                           ` Vlastimil Babka
2014-06-09  9:09                           ` David Rientjes
2014-06-09  9:09                             ` David Rientjes
2014-06-09 11:35                             ` Vlastimil Babka
2014-06-09 11:35                               ` Vlastimil Babka
2014-06-09 22:25                               ` David Rientjes
2014-06-09 22:25                                 ` David Rientjes
2014-06-10  7:26                                 ` Vlastimil Babka
2014-06-10  7:26                                   ` Vlastimil Babka
2014-06-10 23:54                                   ` David Rientjes
2014-06-10 23:54                                     ` David Rientjes
2014-06-11 12:18                                     ` Vlastimil Babka
2014-06-11 12:18                                       ` Vlastimil Babka
2014-06-12  0:21                                       ` David Rientjes
2014-06-12  0:21                                         ` David Rientjes
2014-06-12 11:56                                         ` Vlastimil Babka
2014-06-12 11:56                                           ` Vlastimil Babka
2014-06-12 21:48                                           ` David Rientjes
2014-06-12 21:48                                             ` David Rientjes
2014-06-04 16:11                 ` [RFC PATCH 5/6] mm, compaction: try to capture the just-created high-order freepage Vlastimil Babka
2014-06-04 16:11                   ` Vlastimil Babka
2014-06-04 16:11                 ` [RFC PATCH 6/6] mm, compaction: don't migrate in blocks that cannot be fully compacted in async direct compaction Vlastimil Babka
2014-06-04 16:11                   ` Vlastimil Babka
2014-06-05  0:08                   ` David Rientjes
2014-06-05  0:08                     ` David Rientjes
2014-06-05 15:38                     ` Vlastimil Babka
2014-06-05 15:38                       ` Vlastimil Babka
2014-06-05 21:38                       ` David Rientjes
2014-06-05 21:38                         ` David Rientjes
2014-06-06  7:33                         ` Vlastimil Babka
2014-06-06  7:33                           ` Vlastimil Babka
2014-06-09  9:06                           ` David Rientjes
2014-06-09  9:06                             ` David Rientjes
2014-06-12 12:18                             ` Vlastimil Babka
2014-06-12 12:18                               ` Vlastimil Babka
2014-06-04 23:39                 ` [RFC PATCH 1/6] mm, compaction: periodically drop lock and restore IRQs in scanners David Rientjes
2014-06-04 23:39                   ` David Rientjes
2014-06-05  9:05                   ` Vlastimil Babka
2014-06-05  9:05                     ` Vlastimil Babka
2014-05-22 23:49             ` [PATCH v2] mm, compaction: properly signal and act upon lock and need_sched() contention Kevin Hilman
2014-05-22 23:49               ` Kevin Hilman
2014-05-23  2:48               ` Shawn Guo
2014-05-23  2:48                 ` Shawn Guo
2014-05-23  2:48                 ` Shawn Guo
2014-05-23  8:34                 ` Vlastimil Babka
2014-05-23  8:34                   ` Vlastimil Babka
2014-05-23  8:34                   ` Vlastimil Babka
2014-05-23 10:49                   ` Shawn Guo
2014-05-23 10:49                     ` Shawn Guo
2014-05-23 10:49                     ` Shawn Guo
2014-05-23 15:07                   ` Kevin Hilman
2014-05-23 15:07                     ` Kevin Hilman
2014-05-23 15:07                     ` Kevin Hilman
2014-05-30 16:59                   ` Stephen Warren
2014-05-30 16:59                     ` Stephen Warren
2014-05-30 16:59                     ` Stephen Warren
2014-06-02 13:35                   ` Fabio Estevam
2014-06-02 13:35                     ` Fabio Estevam
2014-06-02 13:35                     ` Fabio Estevam
2014-06-02 14:33                     ` [PATCH -mm] mm, compaction: properly signal and act upon lock and need_sched() contention - fix Vlastimil Babka
2014-06-02 14:33                       ` Vlastimil Babka
2014-06-02 14:33                       ` Vlastimil Babka
2014-06-02 15:18                       ` Fabio Estevam
2014-06-02 15:18                         ` Fabio Estevam
2014-06-02 15:18                         ` Fabio Estevam
2014-06-02 20:09                       ` David Rientjes
2014-06-02 20:09                         ` David Rientjes
2014-06-02 20:09                         ` David Rientjes
2014-05-02 13:16 ` [patch 1/2] mm, migration: add destination page freeing callback Vlastimil Babka
2014-05-02 13:16   ` Vlastimil Babka

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