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[RFC PATCH] mm: use compaction feedback for thp backoff conditions

From Michal Hocko <mhocko@kernel.org>
Newsgroups linux.kernel
Subject [RFC PATCH] mm: use compaction feedback for thp backoff conditions
Date 2016-04-11 18:10 +0200
Message-ID <rmMzw-cS-29@gated-at.bofh.it> (permalink)
References <rkxlf-2sv-9@gated-at.bofh.it> <rkxlh-2sv-49@gated-at.bofh.it> <rmMpQ-8jk-35@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On Mon 11-04-16 17:40:36, Michal Hocko wrote:
> Hi Andrew,
> Vlastimil has pointed out[1] that using compaction_withdrawn() for THP
> allocations has some non-trivial consequences. While I still think that
> the check is OK it is true we shouldn't sneak in a potential behavior
> change into something that basically provides an API. So can you fold
> the following partial revert into the original patch please?
> 
> [1] http://lkml.kernel.org/r/570BB719.2030007@suse.cz

This would be an RFC on top.
---
From 6cfed80ad41f3f1506930b9a3254fe135bf90d4c Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@suse.com>
Date: Mon, 11 Apr 2016 17:51:28 +0200
Subject: [PATCH] mm: use compaction feedback for thp backoff conditions

THP requests skip the direct reclaim if the compaction is either
deferred or contended to reduce stalls which wouldn't help the
allocation success anyway. These checks are ignoring other potential
feedback modes which we have available now.

It clearly doesn't make much sense to go and reclaim few pages if the
previous compaction has failed.

We can also simplify the check by using compaction_withdrawn which
checks for both COMPACT_CONTENDED and COMPACT_DEFERRED. This check
is however covering more reasons why the compaction was withdrawn.
None of them should be a problem for the THP case though.

It is safe to back of if we see COMPACT_SKIPPED because that means
that compaction_suitable failed and a single round of the reclaim is
unlikely to make any difference here. We would have to be close to
the low watermark to reclaim enough and even then there is no guarantee
that the compaction would make any progress while the direct reclaim
would have caused the stall.

COMPACT_PARTIAL_SKIPPED is slightly different because that means that we
have only seen a part of the zone so a retry would make some sense. But
it would be a compaction retry not a reclaim retry to perform. We are
not doing that and that might indeed lead to situations where THP fails
but this should happen only rarely and it would be really hard to
measure.

Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 mm/page_alloc.c | 27 ++++++++-------------------
 1 file changed, 8 insertions(+), 19 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5eae9e0555ed..6d1da0ceaf1e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3420,25 +3420,14 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 	if (order && compaction_made_progress(compact_result))
 		compaction_retries++;
 
-	/* Checks for THP-specific high-order allocations */
-	if (is_thp_gfp_mask(gfp_mask)) {
-		/*
-		 * If compaction is deferred for high-order allocations, it is
-		 * because sync compaction recently failed. If this is the case
-		 * and the caller requested a THP allocation, we do not want
-		 * to heavily disrupt the system, so we fail the allocation
-		 * instead of entering direct reclaim.
-		 */
-		if (compact_result == COMPACT_DEFERRED)
-			goto nopage;
-
-		/*
-		 * Compaction is contended so rather back off than cause
-		 * excessive stalls.
-		 */
-		if(compact_result == COMPACT_CONTENDED)
-			goto nopage;
-	}
+	/*
+	 * Checks for THP-specific high-order allocations and back off
+	 * if the the compaction backed off or failed
+	 */
+	if (is_thp_gfp_mask(gfp_mask) &&
+			(compaction_withdrawn(compact_result) ||
+			 compaction_failed(compact_result)))
+		goto nopage;
 
 	/* Try direct reclaim and then allocating */
 	page = __alloc_pages_direct_reclaim(gfp_mask, order, alloc_flags, ac,
-- 
2.8.0.rc3

-- 
Michal Hocko
SUSE Labs

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Thread

[PATCH 00/11] oom detection rework v5 Michal Hocko <mhocko@kernel.org> - 2016-04-05 13:30 +0200
  [PATCH 10/11] mm, oom: protect !costly allocations some more Michal Hocko <mhocko@kernel.org> - 2016-04-05 13:30 +0200
    Re: [PATCH 10/11] mm, oom: protect !costly allocations some more Andrew Morton <akpm@linux-foundation.org> - 2016-04-06 02:10 +0200
      Re: [PATCH 10/11] mm, oom: protect !costly allocations some more Michal Hocko <mhocko@kernel.org> - 2016-04-06 11:30 +0200
    Re: [PATCH 10/11] mm, oom: protect !costly allocations some more Vlastimil Babka <vbabka@suse.cz> - 2016-04-11 16:50 +0200
  [PATCH 08/11] mm, compaction: Simplify __alloc_pages_direct_compact feedback interface Michal Hocko <mhocko@kernel.org> - 2016-04-05 13:30 +0200
    Re: [PATCH 08/11] mm, compaction: Simplify  __alloc_pages_direct_compact feedback interface Vlastimil Babka <vbabka@suse.cz> - 2016-04-11 16:00 +0200
  [PATCH 04/11] mm, compaction: cover all compaction mode in compact_zone Michal Hocko <mhocko@kernel.org> - 2016-04-05 13:30 +0200
  [PATCH 05/11] mm, compaction: distinguish COMPACT_DEFERRED from COMPACT_SKIPPED Michal Hocko <mhocko@kernel.org> - 2016-04-05 13:30 +0200
    Re: [PATCH 05/11] mm, compaction: distinguish COMPACT_DEFERRED from  COMPACT_SKIPPED Vlastimil Babka <vbabka@suse.cz> - 2016-04-11 13:10 +0200
      Re: [PATCH 05/11] mm, compaction: distinguish COMPACT_DEFERRED from  COMPACT_SKIPPED Michal Hocko <mhocko@kernel.org> - 2016-04-11 13:30 +0200
  [PATCH 07/11] mm, compaction: Update compaction_result ordering Michal Hocko <mhocko@kernel.org> - 2016-04-05 13:30 +0200
    Re: [PATCH 07/11] mm, compaction: Update compaction_result ordering Vlastimil Babka <vbabka@suse.cz> - 2016-04-11 14:20 +0200
  [PATCH 02/11] mm: throttle on IO only when there are too many dirty and writeback pages Michal Hocko <mhocko@kernel.org> - 2016-04-05 13:30 +0200
  [PATCH 01/11] mm, oom: rework oom detection Michal Hocko <mhocko@kernel.org> - 2016-04-05 13:30 +0200
  [PATCH 03/11] mm, compaction: change COMPACT_ constants into enum Michal Hocko <mhocko@kernel.org> - 2016-04-05 13:30 +0200
  [PATCH 06/11] mm, compaction: distinguish between full and partial COMPACT_COMPLETE Michal Hocko <mhocko@kernel.org> - 2016-04-05 13:30 +0200
    Re: [PATCH 06/11] mm, compaction: distinguish between full and  partial COMPACT_COMPLETE Vlastimil Babka <vbabka@suse.cz> - 2016-04-11 14:20 +0200
      Re: [PATCH 06/11] mm, compaction: distinguish between full and  partial COMPACT_COMPLETE Michal Hocko <mhocko@kernel.org> - 2016-04-11 14:50 +0200
        Re: [PATCH 06/11] mm, compaction: distinguish between full and  partial COMPACT_COMPLETE Vlastimil Babka <vbabka@suse.cz> - 2016-04-11 15:00 +0200
          Re: [PATCH 06/11] mm, compaction: distinguish between full and  partial COMPACT_COMPLETE Michal Hocko <mhocko@kernel.org> - 2016-04-11 15:30 +0200
            Re: [PATCH 06/11] mm, compaction: distinguish between full and  partial COMPACT_COMPLETE Vlastimil Babka <vbabka@suse.cz> - 2016-04-11 15:50 +0200
              Re: [PATCH 06/11] mm, compaction: distinguish between full and  partial COMPACT_COMPLETE Michal Hocko <mhocko@kernel.org> - 2016-04-11 15:50 +0200
  [PATCH 09/11] mm, compaction: Abstract compaction feedback to helpers Michal Hocko <mhocko@kernel.org> - 2016-04-05 13:30 +0200
    Re: [PATCH 09/11] mm, compaction: Abstract compaction feedback to  helpers Andrew Morton <akpm@linux-foundation.org> - 2016-04-06 02:00 +0200
      Re: [PATCH 09/11] mm, compaction: Abstract compaction feedback to  helpers Hugh Dickins <hughd@google.com> - 2016-04-06 03:00 +0200
        Re: [PATCH 09/11] mm, compaction: Abstract compaction feedback to  helpers Michal Hocko <mhocko@kernel.org> - 2016-04-06 11:30 +0200
        Re: [PATCH 09/11] mm, compaction: Abstract compaction feedback to  helpers Andrew Morton <akpm@linux-foundation.org> - 2016-04-06 19:50 +0200
    Re: [PATCH 09/11] mm, compaction: Abstract compaction feedback to  helpers Vlastimil Babka <vbabka@suse.cz> - 2016-04-11 16:40 +0200
      Re: [PATCH 09/11] mm, compaction: Abstract compaction feedback to  helpers Michal Hocko <mhocko@kernel.org> - 2016-04-11 17:20 +0200
        Re: [PATCH 09/11] mm, compaction: Abstract compaction feedback to  helpers Michal Hocko <mhocko@kernel.org> - 2016-04-11 17:40 +0200
        Re: [PATCH 09/11] mm, compaction: Abstract compaction feedback to  helpers Vlastimil Babka <vbabka@suse.cz> - 2016-04-12 14:00 +0200
          Re: [PATCH 09/11] mm, compaction: Abstract compaction feedback to  helpers Michal Hocko <mhocko@kernel.org> - 2016-04-12 14:30 +0200
    Re: [PATCH 09/11] mm, compaction: Abstract compaction feedback to  helpers Michal Hocko <mhocko@kernel.org> - 2016-04-11 18:00 +0200
      [RFC PATCH] mm: use compaction feedback for thp backoff conditions Michal Hocko <mhocko@kernel.org> - 2016-04-11 18:10 +0200
      Re: [PATCH 09/11] mm, compaction: Abstract compaction feedback to  helpers Vlastimil Babka <vbabka@suse.cz> - 2016-04-12 14:00 +0200
  [PATCH 11/11] mm: consider compaction feedback also for costly allocation Michal Hocko <mhocko@kernel.org> - 2016-04-05 13:30 +0200
    Re: [PATCH 11/11] mm: consider compaction feedback also for costly  allocation Michal Hocko <mhocko@kernel.org> - 2016-04-05 14:50 +0200
    Re: [PATCH 11/11] mm: consider compaction feedback also for costly  allocation Vlastimil Babka <vbabka@suse.cz> - 2016-04-11 17:10 +0200
  Re: [PATCH 00/11] oom detection rework v5 Michal Hocko <mhocko@kernel.org> - 2016-04-05 14:50 +0200

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