From: Johannes Weiner <hannes@cmpxchg.org>
To: JP Kobryn <jp.kobryn@linux.dev>
Cc: akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org,
liam@infradead.org, vbabka@kernel.org, rppt@kernel.org,
surenb@google.com, mhocko@suse.com, jackmanb@google.com,
ziy@nvidia.com, fvdl@google.com, linux-mm@kvack.org,
shakeel.butt@linux.dev, usama.arif@linux.dev,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] mm/page_alloc: use existing highatomic reserves on the buddy fastpath
Date: Tue, 23 Jun 2026 09:39:21 -0400 [thread overview]
Message-ID: <ajqMiVO6J49GsSKh@cmpxchg.org> (raw)
In-Reply-To: <20260623004600.113347-1-jp.kobryn@linux.dev>
On Mon, Jun 22, 2026 at 05:46:00PM -0700, JP Kobryn wrote:
> ALLOC_HIGHATOMIC currently provides both access to MIGRATE_HIGHATOMIC free
> pages and permission to create new highatomic pageblock reserves. This
> makes it unsuitable for the fastpath.
>
> However, the fastpath can reach rmqueue_buddy() while MIGRATE_HIGHATOMIC
> reserves have free pages available. In this situation, the allocation can
> fall back to other migratetypes without trying those reserves first.
>
> Allow high-priority non-blocking allocations to use existing
> MIGRATE_HIGHATOMIC reserves on the buddy fastpath without growing them.
> First tighten the criteria for reserving pageblocks so that growth may only
> occur in the slowpath. Then allow fastpath usage by enabling
> ALLOC_HIGHATOMIC when the GFP mask describes a non-blocking high-priority
> allocation. This logic has been factored out from gfp_to_alloc_flags() to a
> new function gfp_to_alloc_flags_nonblocking().
>
> A UDP receive workload was run with free MIGRATE_HIGHATOMIC pageblocks
> available in the target zone. Before this patch, the workload did not
> consume these blocks. With this patch, eligible order-1 allocations
> reaching the buddy path consumed existing MIGRATE_HIGHATOMIC pageblocks,
> with no highatomic misses observed. The workload did not grow highatomic
> reserves and NAPI page-frag allocations remained healthy with no failures
> or order-0 fallbacks.
>
> Signed-off-by: JP Kobryn <jp.kobryn@linux.dev>
Awesome.
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
next prev parent reply other threads:[~2026-06-23 13:39 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-23 0:46 [PATCH v3] mm/page_alloc: use existing highatomic reserves on the buddy fastpath JP Kobryn
2026-06-23 8:54 ` Vlastimil Babka (SUSE)
2026-06-23 13:39 ` Johannes Weiner [this message]
2026-06-23 21:17 ` Shakeel Butt
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