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Wed, 27 Aug 2025 08:00:42 +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 rsgSFyq7rmiqdQAAD6G6ig (envelope-from ); Wed, 27 Aug 2025 08:00:42 +0000 Message-ID: <6be0c134-b5b0-4ff9-9d2a-4b68f22c3762@suse.cz> Date: Wed, 27 Aug 2025 10:00:42 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm: slub: avoid wake up kswapd in set_track_prepare To: Harry Yoo Cc: Matthew Wilcox , yangshiguang1011@163.com, akpm@linux-foundation.org, cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, glittao@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, yangshiguang , stable@vger.kernel.org References: <20250825121737.2535732-1-yangshiguang1011@163.com> <54d9e5ac-5a51-4901-9b13-4c248aada2d7@suse.cz> Content-Language: en-US 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+fMgqZkBQJnyBr8BQka0IFQAAoJECJPp+fMgqZkqmMQ AIbGN95ptUMUvo6aAdhxaOCHXp1DfIBuIOK/zpx8ylY4pOwu3GRe4dQ8u4XS9gaZ96Gj4bC+ jwWcSmn+TjtKW3rH1dRKopvC07tSJIGGVyw7ieV/5cbFffA8NL0ILowzVg8w1ipnz1VTkWDr 2zcfslxJsJ6vhXw5/npcY0ldeC1E8f6UUoa4eyoskd70vO0wOAoGd02ZkJoox3F5ODM0kjHu Y97VLOa3GG66lh+ZEelVZEujHfKceCw9G3PMvEzyLFbXvSOigZQMdKzQ8D/OChwqig8wFBmV QCPS4yDdmZP3oeDHRjJ9jvMUKoYODiNKsl2F+xXwyRM2qoKRqFlhCn4usVd1+wmv9iLV8nPs 2Db1ZIa49fJet3Sk3PN4bV1rAPuWvtbuTBN39Q/6MgkLTYHb84HyFKw14Rqe5YorrBLbF3rl M51Dpf6Egu1yTJDHCTEwePWug4XI11FT8lK0LNnHNpbhTCYRjX73iWOnFraJNcURld1jL1nV r/LRD+/e2gNtSTPK0Qkon6HcOBZnxRoqtazTU6YQRmGlT0v+rukj/cn5sToYibWLn+RoV1CE Qj6tApOiHBkpEsCzHGu+iDQ1WT0Idtdynst738f/uCeCMkdRu4WMZjteQaqvARFwCy3P/jpK uvzMtves5HvZw33ZwOtMCgbpce00DaET4y/UzsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZ8gcVAUJFhTonwAKCRAiT6fnzIKmZLY8D/9uo3Ut9yi2YCuASWxr7QQZ lJCViArjymbxYB5NdOeC50/0gnhK4pgdHlE2MdwF6o34x7TPFGpjNFvycZqccSQPJ/gibwNA zx3q9vJT4Vw+YbiyS53iSBLXMweeVV1Jd9IjAoL+EqB0cbxoFXvnjkvP1foiiF5r73jCd4PR rD+GoX5BZ7AZmFYmuJYBm28STM2NA6LhT0X+2su16f/HtummENKcMwom0hNu3MBNPUOrujtW khQrWcJNAAsy4yMoJ2Lw51T/5X5Hc7jQ9da9fyqu+phqlVtn70qpPvgWy4HRhr25fCAEXZDp xG4RNmTm+pqorHOqhBkI7wA7P/nyPo7ZEc3L+ZkQ37u0nlOyrjbNUniPGxPxv1imVq8IyycG AN5FaFxtiELK22gvudghLJaDiRBhn8/AhXc642/Z/yIpizE2xG4KU4AXzb6C+o7LX/WmmsWP Ly6jamSg6tvrdo4/e87lUedEqCtrp2o1xpn5zongf6cQkaLZKQcBQnPmgHO5OG8+50u88D9I rywqgzTUhHFKKF6/9L/lYtrNcHU8Z6Y4Ju/MLUiNYkmtrGIMnkjKCiRqlRrZE/v5YFHbayRD dJKXobXTtCBYpLJM4ZYRpGZXne/FAtWNe4KbNJJqxMvrTOrnIatPj8NhBVI0RSJRsbilh6TE m6M14QORSWTLRg== In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 378B52000A X-Stat-Signature: xzomb4wkyfxrkszbc87unydo9fxtno85 X-HE-Tag: 1756281643-12354 X-HE-Meta: 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 bb9e5hpC g0atcMDFv3IbHMkkft0wX4stQiYdetn7qKo5uGP7NMMpxrEoi5PNL9dImDbzY53edwXIUHlB0TTOmfl2g2qzPbx+Vt02od1RQQDW939RY7Rhcf41K71C8BpEzFktqdaSKzvgF7w9mWjoQ6Z3koKEtsiGWAf5VRkgBEsz3d/9ShuaU7dUOY0V+0kvyqTrkeqeEknyYDo0EAd9QwQUFt04J4T04y3JZZQkHzkBO105cv2A0qeflYCSm0R0NZ0iWnLERcmNmH/bPDwKcMieQtfafhSUb4Ck4MMzujz3uJkWQOBGcH9X7KNO60N0o20vPoOvNMoJZRbSSkruThzcruagncjPU/ZAvnAbkmjCuJrG+4o2beEgJjBS7bTsoela2z/A5Bh8Z 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 8/27/25 07:17, Harry Yoo wrote: > On Mon, Aug 25, 2025 at 05:42:52PM +0200, Vlastimil Babka wrote: >> On 8/25/25 14:40, Matthew Wilcox wrote: >> > On Mon, Aug 25, 2025 at 08:17:37PM +0800, yangshiguang1011@163.com wrote: >> >> Avoid deadlock caused by implicitly waking up kswapd by >> >> passing in allocation flags. >> > [...] >> >> + /* Preemption is disabled in ___slab_alloc() */ >> >> + gfp_flags &= ~(__GFP_DIRECT_RECLAIM); >> > >> > If you don't mean __GFP_KSWAPD_RECLAIM here, the explanation needs to >> > be better. >> >> It was suggested by Harry here: >> https://lore.kernel.org/all/aKKhUoUkRNDkFYYb@harry >> >> I think the comment is enough? Disabling preemption means we can't direct >> reclaim, but we can wake up kswapd. If the slab caller context is such that >> we can't, __GFP_KSWAPD_RECLAIM already won't be in the gfp_flags. > > To make it a little bit more verbose, this ^^ explanation can be added to the > changelog? > >> But I think we should mask our also __GFP_NOFAIL and add __GFP_NOWARN? > > That sounds good. > >> (we should get some common helpers for these kinds of gfp flag manipulations >> already) > > Any ideas for its name? > > gfp_dont_try_too_hard(), > gfp_adjust_lightweight(), > gfp_adjust_mayfail(), > ... > > I'm not good at naming :/ Looks like there's already gfp_nested_mask() for these purposes. I'm not sure if it should be allowing GFP_ATOMIC (thus __GFP_HIGH) as it does though. Seems to contradict the comment about not exhausing reserves. Wonder if that was raised during review... The masking out of __GFP_DIRECT_RECLAIM is specific to the slab case so we don't need a helper for that (unless we find other users). It could be then e.g. gfp_nested_mask_noblock() ?