6.6-stable review patch. If anyone has any objections, please let me know.
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From: Thadeu Lima de Souza Cascardo cascardo@igalia.com
commit 6a204d4b14c99232e05d35305c27ebce1c009840 upstream.
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 Reviewed-by: Vlastimil Babka vbabka@suse.cz Tested-by: Sergey Senozhatsky senozhatsky@chromium.org Acked-by: Michal Hocko mhocko@suse.com Cc: Mel Gorman mgorman@techsingularity.net Cc: Matthew Wilcox willy@infradead.org Cc: NeilBrown neilb@suse.de Cc: Thierry Reding thierry.reding@gmail.com Cc: Brendan Jackman jackmanb@google.com Cc: Johannes Weiner hannes@cmpxchg.org Cc: Suren Baghdasaryan surenb@google.com Cc: Zi Yan ziy@nvidia.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/page_alloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3738,7 +3738,7 @@ 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; }