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Fri, 25 Oct 2024 22:35:42 -0700 (PDT) Received: from [2620:0:1008:15:a73a:2b46:3ef7:2150] ([2620:0:1008:15:a73a:2b46:3ef7:2150]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2e8e36a3114sm2562794a91.29.2024.10.25.22.35.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 25 Oct 2024 22:35:42 -0700 (PDT) Date: Fri, 25 Oct 2024 22:35:41 -0700 (PDT) From: David Rientjes To: Yu Zhao cc: Andrew Morton , Vlastimil Babka , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Link Lin Subject: Re: [PATCH mm-unstable v2] mm/page_alloc: keep track of free highatomic In-Reply-To: <20241026033625.2237102-1-yuzhao@google.com> Message-ID: <4abac91f-bb15-b6d3-4c9c-fd66fae39243@google.com> References: <20241026033625.2237102-1-yuzhao@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Stat-Signature: aus73ma7ckmip5iy8nhd9ocpqkdfa3q5 X-Rspamd-Queue-Id: B4B821A0003 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1729920918-29799 X-HE-Meta: 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 gqsxIbeb YtLop/DZC6rS1OUslNmrnC1MvTMtCogLwJdw0zmmCZHCYBYUQC2qGsBxRgFjGr1NoBbZYM7m6FKfYT62atFW2sVFSVuM0fI6XbWJ6q60QEAyvOkcirYdrdszETbxqyG8W7T9aEgYlit6JfICHsKymk5CLLdjN+K5u02G5XqpF04Umd+LiuWbadSK0VVKsHAU3Zesh8Fued4j5lh+T1Wb5eocDvNc/ZuypwmvA+U0QzxTAN2iIYvoNuceG3RBhTn5pC7Vd0nwXXyl+SSL5nAbwQjeFJNMNJo1qm9DKX0FsvxJcR3zl9wa7dALq0Dd5Bfx55LH8zAp8vPlUGUHh7cn+SRmpkdUX15IlNmOwdzvcB3qXfU7fY8yPaG9MSxSY/f/++OztJGYDkMdbvKUc+FeZm8DA1w== X-Bogosity: Ham, tests=bogofilter, spamicity=0.034101, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 25 Oct 2024, Yu Zhao wrote: > OOM kills due to vastly overestimated free highatomic reserves were > observed: > > ... invoked oom-killer: gfp_mask=0x100cca(GFP_HIGHUSER_MOVABLE), order=0 ... > Node 0 Normal free:1482936kB boost:0kB min:410416kB low:739404kB high:1068392kB reserved_highatomic:1073152KB ... > Node 0 Normal: 1292*4kB (ME) 1920*8kB (E) 383*16kB (UE) 220*32kB (ME) 340*64kB (E) 2155*128kB (UE) 3243*256kB (UE) 615*512kB (U) 1*1024kB (M) 0*2048kB 0*4096kB = 1477408kB > > The second line above shows that the OOM kill was due to the following > condition: > > free (1482936kB) - reserved_highatomic (1073152kB) = 409784KB < min (410416kB) > > And the third line shows there were no free pages in any > MIGRATE_HIGHATOMIC pageblocks, which otherwise would show up as type > 'H'. Therefore __zone_watermark_unusable_free() underestimated the > usable free memory by over 1GB, which resulted in the unnecessary OOM > kill above. > > The comments in __zone_watermark_unusable_free() warns about the > potential risk, i.e., > > If the caller does not have rights to reserves below the min > watermark then subtract the high-atomic reserves. This will > over-estimate the size of the atomic reserve but it avoids a search. > > However, it is possible to keep track of free pages in reserved > highatomic pageblocks with a new per-zone counter nr_free_highatomic > protected by the zone lock, to avoid a search when calculating the > usable free memory. And the cost would be minimal, i.e., simple > arithmetics in the highatomic alloc/free/move paths. > > Reported-by: Link Lin > Signed-off-by: Yu Zhao Acked-by: David Rientjes