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Tue, 23 Jun 2026 06:39:22 -0700 (PDT) Received: from localhost ([2603:7001:f100:500:365a:60ff:fe62:ff29]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-8df82b67affsm126378406d6.45.2026.06.23.06.39.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 23 Jun 2026 06:39:22 -0700 (PDT) Date: Tue, 23 Jun 2026 09:39:21 -0400 From: Johannes Weiner To: JP Kobryn 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 Message-ID: References: <20260623004600.113347-1-jp.kobryn@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260623004600.113347-1-jp.kobryn@linux.dev> X-Stat-Signature: yask14kzbr8x9de5w984tu8dzy8bon4i X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: EBE7216000C X-HE-Tag: 1782221963-767892 X-HE-Meta: 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 Xr3ToEFy H6+0GgYHMvFuvF9Ffb0U8U4lAoDny8p+/cJx060A+NI14BOCNBsXwOLjTfyUXZSkYzh65/+n8fyLqbZ217qN3iz82lGENhZU54WqDmU6auI/YEVPTALKyn6z/RwWZYCBdSzGNbUHU3JejrlcERgApgFymzTJ6/lq4QIPV8qzSNvdNZVgKXau7G+4Lrr2Iiif4ONOj7kwE59HUFUpRyXAH4SvjjwAPgs1DG1li0emMue88dQqrcEwzIkg+d37VyUBGQvBMdxEAeIdH4pNjuX9Wrw+jywdiHaNAm9TbLIlObAOjlmIBVpClrMqRHpG47wyrJbg82HBctgIj+khDV7g7ZQ0dy3ojrnTaT+79bSlhSMGekVIZ9jr/c/gt3igOkTlSCbSy/HVuxgL6xz//f82VekdkO9KRB+OMEHXbLrm+OBh/LFYMga8CXrtDDeCJtVX38rvMMdjEUCGGJU/m4LSlhQ3NdkBZHZMxe6pX Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 Awesome. Acked-by: Johannes Weiner