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Fri, 24 Nov 2023 11:24:13 -0800 (PST) Received: from [2620:0:1008:15:d807:a0b3:20ea:f28f] ([2620:0:1008:15:d807:a0b3:20ea:f28f]) by smtp.gmail.com with ESMTPSA id q12-20020a170902a3cc00b001cf53c235c6sm3597218plb.34.2023.11.24.11.24.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 24 Nov 2023 11:24:12 -0800 (PST) Date: Fri, 24 Nov 2023 11:24:11 -0800 (PST) From: David Rientjes To: Charan Teja Kalla cc: akpm@linux-foundation.org, mgorman@techsingularity.net, mhocko@suse.com, david@redhat.com, vbabka@suse.cz, hannes@cmpxchg.org, quic_pkondeti@quicinc.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH V3 1/2] mm: page_alloc: correct high atomic reserve calculations In-Reply-To: <1660034138397b82a0a8b6ae51cbe96bd583d89e.1700821416.git.quic_charante@quicinc.com> Message-ID: References: <1660034138397b82a0a8b6ae51cbe96bd583d89e.1700821416.git.quic_charante@quicinc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 67C27120015 X-Stat-Signature: 6ieu1wbgjrjucutb4xxx4m6n5ut87p6w X-Rspam-User: X-HE-Tag: 1700853854-645416 X-HE-Meta: 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 lq4sFrR8 Gk6dyGaItdghM6vm1amQZAtLbV2W6jp2mRaGlXkEdiWWsikr+8D2e+c+C9L4zqc2JlfRT/c2xyyQAds+MnMtLi+dkETQHEbUTkeTBOYZ9vi59xBXcxbfImE/E5MU7Me71Crhj2YmzNMhySBEITZBnEDOpgjOB58crFPN058NQERuVak+Ht0PrwyaAhBffwlxdT0jvMo1WZRv94lxMLZt5moa3+yU/Fdq0u9HAJSjfQBUmdpV6jQoLODw1iNcgBkpr2F9mEwgbIbbVVYs/3lQgK4wnS7sXveR+IQWNCPEZJWaH12iJwbFmIgo6A4J8n/XoOxT9HHLi87uOGm34OqabgGBrb/89I/fKCYeeNsSRmV6QIfA6oH8ef3vRxp6m05YhGJxUqLs/jubG5+mp5CEqa7urkKMAWY2oJ4XGDRmcvddwsUrSzv3ygNOjzxgxegtSzZmuINg2KtYM/jn3Nml3aRVFqwquxIaxHvbKMYrbifiKs4MdjPAP/ylmVECL4KLxiouBIvAUBO2Oq/95laF4pa9KgypWX5FXpT5UvKvdqAYRbMRNLS6/rJXAig== X-Bogosity: Ham, tests=bogofilter, spamicity=0.002662, 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, 24 Nov 2023, Charan Teja Kalla wrote: > reserve_highatomic_pageblock() aims to reserve the 1% of the managed > pages of a zone, which is used for the high order atomic allocations. > > It uses the below calculation to reserve: > static void reserve_highatomic_pageblock(struct page *page, ....) { > > ....... > max_managed = (zone_managed_pages(zone) / 100) + pageblock_nr_pages; > > if (zone->nr_reserved_highatomic >= max_managed) > goto out; > > zone->nr_reserved_highatomic += pageblock_nr_pages; > set_pageblock_migratetype(page, MIGRATE_HIGHATOMIC); > move_freepages_block(zone, page, MIGRATE_HIGHATOMIC, NULL); > > out: > .... > } > > Since we are always appending the 1% of zone managed pages count to > pageblock_nr_pages, the minimum it is turning into 2 pageblocks as the > nr_reserved_highatomic is incremented/decremented in pageblock sizes. > > Encountered a system(actually a VM running on the Linux kernel) with the > below zone configuration: > Normal free:7728kB boost:0kB min:804kB low:1004kB high:1204kB > reserved_highatomic:8192KB managed:49224kB > > The existing calculations making it to reserve the 8MB(with pageblock > size of 4MB) i.e. 16% of the zone managed memory. Reserving such high > amount of memory can easily exert memory pressure in the system thus may > lead into unnecessary reclaims till unreserving of high atomic reserves. > > Since high atomic reserves are managed in pageblock size granules, as > MIGRATE_HIGHATOMIC is set for such pageblock, fix the calculations for > high atomic reserves as, minimum is pageblock size , maximum is > approximately 1% of the zone managed pages. > > Acked-by: Mel Gorman > Signed-off-by: Charan Teja Kalla Acked-by: David Rientjes