+ mm-page_alloc-only-set-alloc_highatomic-for-__gpf_high-allocations.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/page_alloc: only set ALLOC_HIGHATOMIC for __GPF_HIGH allocations
has been added to the -mm mm-new branch.  Its filename is
     mm-page_alloc-only-set-alloc_highatomic-for-__gpf_high-allocations.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_alloc-only-set-alloc_highatomic-for-__gpf_high-allocations.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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patches, and acceptance into mm-new is a notification for others take
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------------------------------------------------------
From: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
Subject: mm/page_alloc: only set ALLOC_HIGHATOMIC for __GPF_HIGH allocations
Date: Thu, 14 Aug 2025 14:22:45 -0300

Commit 524c48072e56 ("mm/page_alloc: rename ALLOC_HIGH to
ALLOC_MIN_RESERVE") is the start of a series that explains how __GFP_HIGH,
which implies ALLOC_MIN_RESERVE, is going to be used instead of
__GFP_ATOMIC for high atomic reserves.

Commit eb2e2b425c69 ("mm/page_alloc: explicitly record high-order atomic
allocations in alloc_flags") introduced ALLOC_HIGHATOMIC for such
allocations of order higher than 0.  It still used __GFP_ATOMIC, though.

Then, commit 1ebbb21811b7 ("mm/page_alloc: explicitly define how
__GFP_HIGH non-blocking allocations accesses reserves") just turned that
check for !__GFP_DIRECT_RECLAIM, ignoring that high atomic reserves were
expected to test for __GFP_HIGH.

This leads to high atomic reserves being added for high-order GFP_NOWAIT
allocations and others that clear __GFP_DIRECT_RECLAIM, which is
unexpected.  Later, those reserves lead to 0-order allocations going to
the slow path and starting reclaim.

From /proc/pagetypeinfo, without the patch:

Node    0, zone      DMA, type   HighAtomic      0      0      0      0      0      0      0      0      0      0      0
Node    0, zone    DMA32, type   HighAtomic      1      8     10      9      7      3      0      0      0      0      0
Node    0, zone   Normal, type   HighAtomic     64     20     12      5      0      0      0      0      0      0      0

With the patch:

Node    0, zone      DMA, type   HighAtomic      0      0      0      0      0      0      0      0      0      0      0
Node    0, zone    DMA32, type   HighAtomic      0      0      0      0      0      0      0      0      0      0      0
Node    0, zone   Normal, type   HighAtomic      0      0      0      0      0      0      0      0      0      0      0

Link: https://lkml.kernel.org/r/20250814172245.1259625-1-cascardo@igalia.com
Fixes: 1ebbb21811b7 ("mm/page_alloc: explicitly define how __GFP_HIGH non-blocking allocations accesses reserves")
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
Tested-by: Helen Koike <koike@igalia.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: NeilBrown <neilb@suse.de>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/page_alloc.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/page_alloc.c~mm-page_alloc-only-set-alloc_highatomic-for-__gpf_high-allocations
+++ a/mm/page_alloc.c
@@ -4408,7 +4408,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask, unsig
 		if (!(gfp_mask & __GFP_NOMEMALLOC)) {
 			alloc_flags |= ALLOC_NON_BLOCK;
 
-			if (order > 0)
+			if (order > 0 && (alloc_flags & ALLOC_MIN_RESERVE))
 				alloc_flags |= ALLOC_HIGHATOMIC;
 		}
 
_

Patches currently in -mm which might be from cascardo@igalia.com are

mm-page_alloc-only-set-alloc_highatomic-for-__gpf_high-allocations.patch