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mm/page_alloc: let GFP_ATOMIC order-0 allocs access highatomic reserves
Under memory pressure it's possible for GFP_ATOMIC order-0 allocations to fail even though free pages are available in the highatomic reserves. GFP_ATOMIC allocations cannot trigger unreserve_highatomic_pageblock() since it's only run from reclaim. Given that such allocations will pass the watermarks in __zone_watermark_unusable_free(), it makes sense to fallback to highatomic reserves the same way that ALLOC_OOM can. This fixes order-0 page allocation failures observed on Cloudflare's fleet when handling network packets: kswapd1: page allocation failure: order:0, mode:0x820(GFP_ATOMIC), nodemask=(null),cpuset=/,mems_allowed=0-7 CPU: 10 PID: 696 Comm: kswapd1 Kdump: loaded Tainted: G O 6.6.43-CUSTOM #1 Hardware name: MACHINE Call Trace: <IRQ> dump_stack_lvl+0x3c/0x50 warn_alloc+0x13a/0x1c0 __alloc_pages_slowpath.constprop.0+0xc9d/0xd10 __alloc_pages+0x327/0x340 __napi_alloc_skb+0x16d/0x1f0 bnxt_rx_page_skb+0x96/0x1b0 [bnxt_en] bnxt_rx_pkt+0x201/0x15e0 [bnxt_en] __bnxt_poll_work+0x156/0x2b0 [bnxt_en] bnxt_poll+0xd9/0x1c0 [bnxt_en] __napi_poll+0x2b/0x1b0 bpf_trampoline_6442524138+0x7d/0x1000 __napi_poll+0x5/0x1b0 net_rx_action+0x342/0x740 handle_softirqs+0xcf/0x2b0 irq_exit_rcu+0x6c/0x90 sysvec_apic_timer_interrupt+0x72/0x90 </IRQ> [mfleming@cloudflare.com: update comment] Link: https://lkml.kernel.org/r/20241015125158.3597702-1-matt@readmodwrite.com Link: https://lkml.kernel.org/r/20241011120737.3300370-1-matt@readmodwrite.com Link: https://lore.kernel.org/all/CAGis_TWzSu=P7QJmjD58WWiu3zjMTVKSzdOwWE8ORaGytzWJwQ@mail.gmail.com/ Fixes: 1d91df85f399 ("mm/page_alloc: handle a missing case for memalloc_nocma_{save/restore} APIs") Signed-off-by: Matt Fleming <mfleming@cloudflare.com> Suggested-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Michal Hocko <mhocko@kernel.org> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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@ -2893,12 +2893,12 @@ struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone,
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page = __rmqueue(zone, order, migratetype, alloc_flags);
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/*
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* If the allocation fails, allow OOM handling access
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* to HIGHATOMIC reserves as failing now is worse than
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* failing a high-order atomic allocation in the
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* future.
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* If the allocation fails, allow OOM handling and
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* order-0 (atomic) allocs access to HIGHATOMIC
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* reserves as failing now is worse than failing a
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* high-order atomic allocation in the future.
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*/
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if (!page && (alloc_flags & ALLOC_OOM))
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if (!page && (alloc_flags & (ALLOC_OOM|ALLOC_NON_BLOCK)))
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page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC);
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if (!page) {
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