Re: [PATCH RFC 1/2] mm, page_alloc, thp: prevent reclaim for __GFP_THISNODE THP allocations

[Zi Yan <ziy@nvidia.com>]

On 16 Dec 2025, at 10:54, Vlastimil Babka wrote:

> Since commit cc638f329ef6 ("mm, thp: tweak reclaim/compaction effort of
> local-only and all-node allocations"), THP page fault allocations have
> settled on the following scheme (from the commit log):
>
> 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
>
> Recent customer reports however revealed we have a gap in step 1 above.
> What we have seen is excessive reclaim due to THP page faults on a NUMA
> node that's close to its high watermark, while other nodes have plenty
> of free memory.
>
> The problem with step 1 is that it promises no reclaim after the
> compaction attempt, however reclaim is only avoided for certain
> compaction outcomes (deferred, or skipped due to insufficient free base
> pages), and not e.g. when compaction is actually performed but fails (we
> did see compact_fail vmstat counter increasing).
>
> THP page faults can therefore exhibit a zone_reclaim_mode-like behavior,
> which is not the intention.
>
> Thus add a check for __GFP_THISNODE that corresponds to this exact
> situation and prevents continuing with reclaim/compaction once the
> initial compaction attempt isn't successful in allocating the page.
>
> Note that commit cc638f329ef6 has not introduced this over-reclaim
> possibility; it appears to exist in some form since commit 2f0799a0ffc0
> ("mm, thp: restore node-local hugepage allocations"). Followup commits
> b39d0ee2632d ("mm, page_alloc: avoid expensive reclaim when compaction
> may not succeed") and cc638f329ef6 have moved in the right direction,
> but left the abovementioned gap.
>
> Fixes: 2f0799a0ffc0 ("mm, thp: restore node-local hugepage allocations")
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> ---
>  mm/page_alloc.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
>
LGTM. Acked-by: Zi Yan <ziy@nvidia.com>

Best Regards,
Yan, Zi