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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Wed, Oct 28, 2026 at 01:15:53PM -0400, Johannes Weiner wrote: > 281dd25c1a01 ("mm/page_alloc: let GFP_ATOMIC order-0 allocs access > highatomic reserves") accidentally gave all non-blocking allocation > requests access to highatomic reserves, which includes GFP_NOWAIT and > other sites clearing __GFP_DIRECT_RECLAIM. > > While this improved atomic request success rate, it's unintentionally > broad and can actually worsen highatomic requests by squandering the > reserves on requests that don't need it. > > There are concurrent efforts to clear __GFP_DIRECT_RECLAIM altogether > for costly order __GFP_NORETRY requests, which would then also fall > into this exemption and deplete reserves even faster. > > What GFP_ATOMIC has over the others is __GFP_HIGH, which > alloc_flags_slowpath() translates to ALLOC_MIN_RESERVE. > > Narrow the exemption to contexts that have both ALLOC_NON_BLOCK | > ALLOC_MIN_RESERVE. > > Reported-by: Sashiko > Link: https://sashiko.dev/#/patchset/20260904115629.3993331-1-dipiets@amazon.it > Fixes: 281dd25c1a01 ("mm/page_alloc: let GFP_ATOMIC order-0 allocs access highatomic reserves") > Cc: stable@vger.kernel.org > Signed-off-by: Johannes Weiner > --- > mm/page_alloc.c | 4 +++- > mm/page_alloc.h | 3 +++ > 2 files changed, 6 insertions(+), 1 deletion(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index a8cac5e01066..8ac2e2bf14fc 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3238,7 +3238,9 @@ struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone, > * reserves as failing now is worse than failing a > * high-order atomic allocation in the future. > */ > - if (!page && (alloc_flags & (ALLOC_OOM|ALLOC_NON_BLOCK))) > + if (!page && > + ((alloc_flags & ALLOC_OOM) || > + (alloc_flags & ALLOC_MASK_ATOMIC) == ALLOC_MASK_ATOMIC)) > page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC); > > if (!page) { > diff --git a/mm/page_alloc.h b/mm/page_alloc.h > index e238ee91ed24..9c3c2830acb0 100644 > --- a/mm/page_alloc.h > +++ b/mm/page_alloc.h > @@ -60,6 +60,9 @@ > /* Flags that allow allocations below the min watermark. */ > #define ALLOC_RESERVES (ALLOC_NON_BLOCK|ALLOC_MIN_RESERVE|ALLOC_HIGHATOMIC|ALLOC_OOM) > > +/* Flags that mean GFP_ATOMIC */ > +#define ALLOC_MASK_ATOMIC (ALLOC_NON_BLOCK|ALLOC_MIN_RESERVE) > + > /* > * Structure for holding the mostly immutable allocation parameters passed > * between functions involved in allocations, including the alloc_pages* I feel patch 2 needs to come first, so that __zone_watermark_unusable_free() accounts correctly. Acked-by: Balbir Singh