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Wed, 15 Jan 2025 17:17:50 +0800 (CST) Message-ID: <0347ff02-eac4-4fa5-88c3-6d12988438d1@126.com> Date: Wed, 15 Jan 2025 17:17:50 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V3] mm: compaction: skip memory compaction when there are not enough migratable pages To: Vlastimil Babka , akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, 21cnbao@gmail.com, david@redhat.com, baolin.wang@linux.alibaba.com, hannes@cmpxchg.org, liuzixing@hygon.cn References: <1736335854-548-1-git-send-email-yangge1116@126.com> <39709cd7-0de6-4247-a70a-9f81fccbce6a@suse.cz> <1ada3f6d-72bb-46a4-9fef-0bf6a7b32e62@suse.cz> From: Ge Yang In-Reply-To: <1ada3f6d-72bb-46a4-9fef-0bf6a7b32e62@suse.cz> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-CM-TRANSID:_____wB31P0+fYdn0+MaBA--.26710S2 X-Coremail-Antispam: 1Uf129KBjvJXoWxCrW3AF1kCr4DJrWUKF4xCrg_yoW5GF4Dpa yUWFsF9FZ5XF43Aw1vyw4vgF1Ykw4xGryUJrnaqryDuwsI9FyI9FWIyFWUCayUXr4ftFWj vFW0gFy7AFsIva7anT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x07jbPEfUUUUU= X-Originating-IP: [112.64.138.194] X-CM-SenderInfo: 51dqwwjhrrila6rslhhfrp/1tbifgvVG2eHcDbhdAAAsI X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: ED60E180007 X-Stat-Signature: uaensx3ek1c5hpzusggu5nphmbh8jfun X-Rspam-User: X-HE-Tag: 1736932680-434713 X-HE-Meta: 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 qjdrp61S jQs8nQXKnW0Xxk20xWe0wf+c3g/eL0sk9bq9SLN6nTdP14Yw4w5x25AVLCmEi1XZSqgIIEzwo1o+f8QhFxsbARmwLyCkCkwejZKRS6Fp9YdEQOaiCTvxrdvWjQG/pz+fKgpO2kJFxzARcBnQJodaTnat2XQN3kEp928gfCpJyOObsltjDkKfP2824ZtYZ96GluL3tzK+2SYlQAN+6w94myEL+SBN3CBbCuHI9X2H+wW4whkMaUGM7v68X3IfuNhBfy1JRlOONyAqu5qsrwLkNP4d6V2RNQjUN1ARjp7W+2iT2Ed5UC4bRebYrvKstpGyUcgE0amKkhd12m0ZDAv5ertD+RBfB2C/r6CELwUZwqq0Y3gnWjmvmOoJ5E1HMcMbYUk0VA7uorLcbspjN3dijJ3wXJLO+EyA/nhZh 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: 在 2025/1/14 20:51, Vlastimil Babka 写道: > On 1/14/25 13:24, Ge Yang wrote: >>> Hopefully also when done from the pin_user_pages_remote(..., FOLL_LONGTERM, >>> ...) context the allocation gfp_mask correctly lacks __GFP_MOVABLE? >> yes. >> I guess >>> it has to, otherwise it would allocate from the CMA pageblocks. >>> >>> Then I wonder if we could use the real allocation context to determine >>> watermarks, as __compaction_suitable() is passing ALLOC_CMA instead because >>> it's checking only for migration targets, which have to be CMA compatible by >>> definition. But we could use the real unmovable allocation context to have >>> __zone_watermark_unusable_free() subtract CMA pages, and thus we won't pass >>> the order-0 check anymore once the non-CMA part is exhausted. >>> >>> There's some risk that in some different scenario the compaction could in >>> fact migrate pages from the exhausted non-CMA part of the zone to the CMA >>> part and succeed, and we'll skip it instead. But that should be rare? >>> >> Below is the previous discussion： >> https://lore.kernel.org/lkml/1734436004-1212-1-git-send-email-yangge1116@126.com/ > > Right so Johannes had the same concern. > >>> Anyway given that concern I'm not sure about changing >>> __compaction_suitable() for every caller like this. We could (at least >>> initially) target this heuristic only for COMPACT_PRIO_ASYNC which is being >>> used for this THP opportunistic attempt. >>> >>> So for example: >>> - add a new bool flag to compact_control that is true for COMPACT_PRIO_ASYNC >>> - pass cc pointer to compaction_suit_allocation_order() >>> - in that function, add another check if the the new cc flag is true, >>> between the current zone_watermark_ok() and compaction_suitable() checks, >>> which works like __compaction_suitable() but uses alloc_flags (which should >>> not be ALLOC_CMA in our pinned allocation case) instead of ALLOC_CMA, return >>> COMPACT_SKIPPED if it fails. >>> >> I will send a new version of the patch based on the suggestions here. >> Thank you. > > Yeah that way should hopefully limit the concern sufficiently. Maybe we > could also add costly_order condition in addition to COMPACT_PRIO_ASYNC > condition to set the new compact_control flag. But only __GFP_NORETRY > allocations should be affected in the immediate "goto nopage" when > compaction is skipped, others will attempt with DEF_COMPACT_PRIORITY anyway > and won't fail without trying to compact-migrate the non-CMA pageblocks into > CMA pageblocks first, so it should be fine. Ok, thanks.