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Message-ID: <0f46ff18-e385-4940-b0f0-db4130704bfb@suse.cz>
Date: Mon, 14 Oct 2024 12:37:44 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Matt Fleming <matt@...dmodwrite.com>
Cc: linux-kernel@...r.kernel.org, kernel-team@...udflare.com,
Matt Fleming <mfleming@...udflare.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Mel Gorman <mgorman@...hsingularity.net>, linux-mm@...ck.org,
Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH] mm/page_alloc: Let GFP_ATOMIC order-0 allocs access
highatomic reserves
On 10/11/24 14:07, Matt Fleming wrote:
> From: Matt Fleming <mfleming@...udflare.com>
>
> 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>
>
> Suggested-by: Vlastimil Babka <vbabka@...e.cz>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Mel Gorman <mgorman@...hsingularity.net>
> Cc: linux-mm@...ck.org
> Link: https://lore.kernel.org/all/CAGis_TWzSu=P7QJmjD58WWiu3zjMTVKSzdOwWE8ORaGytzWJwQ@mail.gmail.com/
> Signed-off-by: Matt Fleming <mfleming@...udflare.com>
Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
(but a comment should be updated, see below)
I think we could add Cc: stable and I believe the commit that broke it was:
Fixes: 1d91df85f399 ("mm/page_alloc: handle a missing case for
memalloc_nocma_{save/restore} APIs")
because it was where an order > 0 condition was introduced to allow
allocation from MIGRATE_HIGHATOMIC
commit eb2e2b425c69 ("mm/page_alloc: explicitly record high-order atomic
allocations in alloc_flags") realized there's a gap for OOM (even if
changelog doesn't mention it) but we should allow the order-0 atomic
allocations to fallback as well.
> ---
> mm/page_alloc.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 8afab64814dc..0c4c359f5ba7 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2898,7 +2898,7 @@ struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone,
> * failing a high-order atomic allocation in the
> * future.
> */
We should also update the comment above to reflect this is no longer just
for the OOM case?
> - if (!page && (alloc_flags & ALLOC_OOM))
> + if (!page && (alloc_flags & (ALLOC_OOM|ALLOC_NON_BLOCK)))
> page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC);
>
> if (!page) {
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