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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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Level: X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; ARC_NA(0.00)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; MIME_TRACE(0.00)[0:+]; RCPT_COUNT_TWELVE(0.00)[12]; RCVD_TLS_ALL(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; FREEMAIL_ENVRCPT(0.00)[163.com,gmail.com]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[infradead.org,163.com,linux-foundation.org,gentwo.org,google.com,linux.dev,gmail.com,kvack.org,vger.kernel.org,xiaomi.com]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,suse.cz:mid] X-Spam-Flag: NO X-Spam-Score: -4.30 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() ?