Commit cc638f32 authored Jan 13, 2020 by Vlastimil Babka Committed by Linus Torvalds Jan 13, 2020

mm, thp: tweak reclaim/compaction effort of local-only and all-node allocations

THP page faults now attempt a __GFP_THISNODE allocation first, which
should only compact existing free memory, followed by another attempt
that can allocate from any node using reclaim/compaction effort
specified by global defrag setting and madvise.

This patch makes the following changes to the scheme:

 - Before the patch, the first allocation relies on a check for
   pageblock order and __GFP_IO to prevent excessive reclaim. This
   however affects also the second attempt, which is not limited to
   single node.

   Instead of that, reuse the existing check for costly order
   __GFP_NORETRY allocations, and make sure the first THP attempt uses
   __GFP_NORETRY. As a side-effect, all costly order __GFP_NORETRY
   allocations will bail out if compaction needs reclaim, while
   previously they only bailed out when compaction was deferred due to
   previous failures.

   This should be still acceptable within the __GFP_NORETRY semantics.

 - Before the patch, the second allocation attempt (on all nodes) was
   passing __GFP_NORETRY. This is redundant as the check for pageblock
   order (discussed above) was stronger. It's also contrary to
   madvise(MADV_HUGEPAGE) which means some effort to allocate THP is
   requested.

   After this patch, the second attempt doesn't pass __GFP_THISNODE nor
   __GFP_NORETRY.

To sum up, THP page faults now try the following attempts:

1. local node only THP allocation with no reclaim, just compaction.
2. for madvised VMA's or when synchronous compaction is enabled always - THP
   allocation from any node with effort determined by global defrag setting
   and VMA madvise
3. fallback to base pages on any node

Link: http://lkml.kernel.org/r/08a3f4dd-c3ce-0009-86c5-9ee51aba8557@suse.cz


Fixes: b39d0ee2 ("mm, page_alloc: avoid expensive reclaim when compaction may not succeed")
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent b3a987b0

mm/mempolicy.c

+7 −3

Original line number	Diff line number	Diff line
		@@ -2148,18 +2148,22 @@ alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma,
		nmask = policy_nodemask(gfp, pol);
		if (!nmask \|\| node_isset(hpage_node, *nmask)) {
		mpol_cond_put(pol);
		/*
		* First, try to allocate THP only on local node, but
		* don't reclaim unnecessarily, just compact.
		*/
		page = __alloc_pages_node(hpage_node,
		gfp \| __GFP_THISNODE, order);
		gfp \| __GFP_THISNODE \| __GFP_NORETRY, order);

		/*
		* If hugepage allocations are configured to always
		* synchronous compact or the vma has been madvised
		* to prefer hugepage backing, retry allowing remote
		* memory as well.
		* memory with both reclaim and compact as well.
		*/
		if (!page && (gfp & __GFP_DIRECT_RECLAIM))
		page = __alloc_pages_node(hpage_node,
		gfp \| __GFP_NORETRY, order);
		gfp, order);

		goto out;
		}

mm/page_alloc.c

+5 −19

Original line number	Diff line number	Diff line
		@@ -4476,8 +4476,11 @@ retry_cpuset:
		if (page)
		goto got_pg;

		if (order >= pageblock_order && (gfp_mask & __GFP_IO) &&
		!(gfp_mask & __GFP_RETRY_MAYFAIL)) {
		/*
		* Checks for costly allocations with __GFP_NORETRY, which
		* includes some THP page fault allocations
		*/
		if (costly_order && (gfp_mask & __GFP_NORETRY)) {
		/*
		* If allocating entire pageblock(s) and compaction
		* failed because all zones are below low watermarks
		@@ -4498,23 +4501,6 @@ retry_cpuset:
		if (compact_result == COMPACT_SKIPPED \|\|
		compact_result == COMPACT_DEFERRED)
		goto nopage;
		}

		/*
		* Checks for costly allocations with __GFP_NORETRY, which
		* includes THP page fault allocations
		*/
		if (costly_order && (gfp_mask & __GFP_NORETRY)) {
		/*
		* 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;

		/*
		* Looks like reclaim/compaction is worth trying, but

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