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Fri, 28 Feb 2025 09:59:20 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id eFPsFPiIwWeQWAAAD6G6ig (envelope-from ); Fri, 28 Feb 2025 09:59:20 +0000 Message-ID: <13614e0a-4985-42a1-87b2-a57237437a08@suse.cz> Date: Fri, 28 Feb 2025 10:59:20 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 2/2] mm/page_alloc: Clarify should_claim_block() commentary Content-Language: en-US To: Brendan Jackman , Andrew Morton Cc: Mel Gorman , Michal Hocko , Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Yosry Ahmed References: <20250228-clarify-steal-v4-0-cb2ef1a4e610@google.com> <20250228-clarify-steal-v4-2-cb2ef1a4e610@google.com> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJkBREIBQkRadznAAoJECJPp+fMgqZkNxIQ ALZRqwdUGzqL2aeSavbum/VF/+td+nZfuH0xeWiO2w8mG0+nPd5j9ujYeHcUP1edE7uQrjOC Gs9sm8+W1xYnbClMJTsXiAV88D2btFUdU1mCXURAL9wWZ8Jsmz5ZH2V6AUszvNezsS/VIT87 AmTtj31TLDGwdxaZTSYLwAOOOtyqafOEq+gJB30RxTRE3h3G1zpO7OM9K6ysLdAlwAGYWgJJ V4JqGsQ/lyEtxxFpUCjb5Pztp7cQxhlkil0oBYHkudiG8j1U3DG8iC6rnB4yJaLphKx57NuQ PIY0Bccg+r9gIQ4XeSK2PQhdXdy3UWBr913ZQ9AI2usid3s5vabo4iBvpJNFLgUmxFnr73SJ KsRh/2OBsg1XXF/wRQGBO9vRuJUAbnaIVcmGOUogdBVS9Sun/Sy4GNA++KtFZK95U7J417/J Hub2xV6Ehc7UGW6fIvIQmzJ3zaTEfuriU1P8ayfddrAgZb25JnOW7L1zdYL8rXiezOyYZ8Fm ZyXjzWdO0RpxcUEp6GsJr11Bc4F3aae9OZtwtLL/jxc7y6pUugB00PodgnQ6CMcfR/HjXlae h2VS3zl9+tQWHu6s1R58t5BuMS2FNA58wU/IazImc/ZQA+slDBfhRDGYlExjg19UXWe/gMcl De3P1kxYPgZdGE2eZpRLIbt+rYnqQKy8UxlszsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZAUSmwUJDK5EZgAKCRAiT6fnzIKmZOJGEACOKABgo9wJXsbWhGWYO7mD 8R8mUyJHqbvaz+yTLnvRwfe/VwafFfDMx5GYVYzMY9TWpA8psFTKTUIIQmx2scYsRBUwm5VI EurRWKqENcDRjyo+ol59j0FViYysjQQeobXBDDE31t5SBg++veI6tXfpco/UiKEsDswL1WAr tEAZaruo7254TyH+gydURl2wJuzo/aZ7Y7PpqaODbYv727Dvm5eX64HCyyAH0s6sOCyGF5/p eIhrOn24oBf67KtdAN3H9JoFNUVTYJc1VJU3R1JtVdgwEdr+NEciEfYl0O19VpLE/PZxP4wX PWnhf5WjdoNI1Xec+RcJ5p/pSel0jnvBX8L2cmniYnmI883NhtGZsEWj++wyKiS4NranDFlA HdDM3b4lUth1pTtABKQ1YuTvehj7EfoWD3bv9kuGZGPrAeFNiHPdOT7DaXKeHpW9homgtBxj 8aX/UkSvEGJKUEbFL9cVa5tzyialGkSiZJNkWgeHe+jEcfRT6pJZOJidSCdzvJpbdJmm+eED w9XOLH1IIWh7RURU7G1iOfEfmImFeC3cbbS73LQEFGe1urxvIH5K/7vX+FkNcr9ujwWuPE9b 1C2o4i/yZPLXIVy387EjA6GZMqvQUFuSTs/GeBcv0NjIQi8867H3uLjz+mQy63fAitsDwLmR EP+ylKVEKb0Q2A== In-Reply-To: <20250228-clarify-steal-v4-2-cb2ef1a4e610@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Stat-Signature: t5mny4stzpb3hs8bg1da7ngx9s5drfxa X-Rspamd-Queue-Id: 3CD0BC0005 X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1740736762-874861 X-HE-Meta: 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 ptKYt3NY HijsKWIxtPE9GEZp5XlRhUWpdogN3dD/OXQtF30qeDspCeVQL59YoEABkoH8GAKCCil4Yy0+DR0pjcXJFAhSiA0c0Qv+fZ42DWpjCpUAiGNCmgaWdovgIyhFuDAEPUOynMO4biNHzGa5TqxoDJyyT+rgCvGisCHzqhPi0nceFlUw8MzZPQ7Dj6vFRIS3SUtkWeupO5zHJM8R+/cNoEttSNDGiSk0CQCGEN3IBoASiI8F2cP3GyI7xf0indCP8EmrqUVaAKWIUUZCqkSk0t9Ph6m9iq7aPugraCl7wciCSsnMwZMaVndWyVbPaaiC2dZHJxoDKW2YmGhMIB2jMXTggtdkO+BlmkUegfhqe 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 2/28/25 10:52, Brendan Jackman wrote: > There's lots of text here but it's a little hard to follow, this is an > attempt to break it up and align its structure more closely with the > code. > > Reword the top-level function comment to just explain what question the > function answers from the point of view of the caller. > > Break up the internal logic into different sections that can have their > own commentary describing why that part of the rationale is present. > > Note the page_group_by_mobility_disabled logic is not explained in the > commentary, that is outside the scope of this patch... > > Signed-off-by: Brendan Jackman Reviewed-by: Vlastimil Babka > + /* > + * Unmovable/reclaimable allocations would cause permanent > + * fragmentations if they fell back to allocating from a movable block > + * (polluting it), so we try to claim the whole block regardless of the > + * allocation size. Later movable allocations can always steal from this > + * block, which is less problematic. > + */ > + if (start_mt == MIGRATE_RECLAIMABLE || start_mt == MIGRATE_UNMOVABLE) > + return true; > + > + if (page_group_by_mobility_disabled) > + return true; > + > + /* > + * Movable pages won't cause permanent fragmentation, so when you alloc s/you/we/ for consistency? I think Andrew can amend locally to avoid resend. Thanks. > + * small pages, we just need to temporarily steal unmovable or > + * reclaimable pages that are closest to the request size. After a > + * while, memory compaction may occur to form large contiguous pages, > + * and the next movable allocation may not need to steal. > + */ > return false; > } > >