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Mon, 27 Jan 2025 14:13:21 +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 mFnvL4GUl2e4QgAAD6G6ig (envelope-from ); Mon, 27 Jan 2025 14:13:21 +0000 Message-ID: <175ea8ba-e681-4de4-811e-c623acfb5e3a@suse.cz> Date: Mon, 27 Jan 2025 15:13:21 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm/compaction: remove low watermark cap for proactive compaction Content-Language: en-US To: =?UTF-8?B?TWljaGHFgiBDxYJhcGnFhHNraQ==?= Cc: Andrew Morton , Nitin Gupta , Pasha Tatashin , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250124182140.2243862-1-mclapinski@google.com> <20250124182140.2243862-2-mclapinski@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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: 92E2C1C0003 X-Rspamd-Server: rspam10 X-Stat-Signature: qcqp96ji4pp4p4rtekyko1kdsf68gfzg X-HE-Tag: 1737987203-327023 X-HE-Meta: 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 TaWs0HGm nRgrwpTdJnoCj/FqKbqAic4t6OiYRAUXzgIbVQ2GaXKTBjnhSTw5hxHObkklQQ2tDfTJVKu5n7XaTSWvhtR/7NugthYmHv4LxCXeFwwUAKM1xfkU0Qeypjb37VXzQGQ/k4/rs4Zg4KB98vSB+zERwRBj0EtwJK/GtxoK2kNyvH8qisAPf9o9nIPoAIOaJ6w9mddwEV3Oqmipl/lFU/t13kMJ+xjcp/Nq0g/A0BREiqimfsrMxnwvFvgXDarhioWwMG9Lrgsi2qX7kdTpn5XVEihl3FpMCS2gKNxzgPSf43t6gWViQBKnxfNNgzQ== 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 1/27/25 14:31, Michał Cłapiński wrote: > On Mon, Jan 27, 2025 at 11:38 AM Vlastimil Babka wrote: >> >> On 1/24/25 19:21, Michal Clapinski wrote: >> > Previously a min cap of 5 has been set in the commit introducing >> > proactive compaction. This was to make sure users don't hurt themselves >> > by setting the proactiveness to 100 and making their system >> > unresponsive. But the compaction mechanism has a backoff mechanism that >> > will sleep for 30s if no progress is made, so I don't see a significant >> > risk here. My system (20GB of memory) has been perfectly fine with >> > proactiveness set to 100 and leeway set to 0. > >> What if you don't set the leeway to 0? > > When the fragmentation score (lower is better) gets larger than the > high watermark, proactive compaction kicks in. Compaction stops when > the score goes below the low watermark (or no progress is made and > backoff kicks in). Leeway is the difference between low and high > watermarks. So the bigger the leeway, the longer we have to wait for > proactive compaction to kick in. Memory usage on the host would also > look more like a sawtooth wave (slowly creeping up then sharp drop). Oh I see, I got the direction opposite mentally, when responding. But that writeup could go in some form to the patch/cover letter :) > I set the leeway to 0 in this example because that's the most > aggressive configuration. My system can't reach a fragmentation score > of 0, so it tries to do compaction as often as possible. And thus thought leeway of 0 means less agressive. >> In other words, should we keep the cap in some sense but make it depend on the leeway? > > I could do something like > wmark_low = max(100U - sysctl_compaction_proactiveness, > min(sysctl_compaction_proactiveness_leeway, 5U)); > and it would have the benefit of not changing the behavior of > proactive compaction for current users. However, it would make it > impossible to have a small low watermark with the default leeway. > That's okay in my case but do we want to create those restrictions for > the future users? With that, the restriction seems unnecessary. Thanks.