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b=xv0qaT2QIVfkwK4h2ETIav75GmLJJKW9kx+fjQFs3cugcISut3h6DP77YW0AVrDIe ykm8iIH3fyYiafgVuC5YSd+qvyoIIbmjFxeoRPceztjerO4+/WX3hlHxbjInHbBT0O wMCLuhEjJ+zsxBeHF/IBEeNux+/8hxp8OjR1dUt8= Date: Fri, 25 Oct 2024 21:24:48 -0700 From: Andrew Morton To: Yu Zhao Cc: David Rientjes , 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 Message-Id: <20241025212448.b1a9069d71df5b497e1b0190@linux-foundation.org> In-Reply-To: <20241026033625.2237102-1-yuzhao@google.com> References: <20241026033625.2237102-1-yuzhao@google.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: oi63qp8qnoe95zewg57se6py3prik1d3 X-Rspamd-Queue-Id: 18AF240003 X-Rspamd-Server: rspam11 X-HE-Tag: 1729916674-653392 X-HE-Meta: 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 MlKQJ3Jv GZLQjws6NSQqVC4wMWrESNxh0lrBinAlWZHqENxku8tHwrFfyunWqdorEa+ARXNGEggkEVtkvMiWcuhgOsCy6MjQasJruQ/9nK37FRFCtm4B7VKkZxs+l5N0jzBjVOOfgXBEJpqoYBh+ByOAPcSnsk3Xpinljlr3F5vQwLEuf5Gz1wElOMPJlS1HA+7LdvgUo5zky/eT85aJaPKLsPCKFAVzrI7guhUHdhf7ViZgIx/ktsYWvaa8OV/TsiuvQTOU61EGIeHHQ67bZPT7Q+sM09I9xQk9EVgUeDG7wQwvt8+TUniFylbTZVnwpjN1wkrPVuTz7 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, 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 21:36:25 -0600 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 Under what circumstances? > 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. Is a -stable backport needed? If so, is a Fixes: target identifiable?