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Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.4.1 Subject: Re: [PATCH v6 6/9] mm: multigenerational lru: aging Content-Language: en-US To: Michal Hocko , Yu Zhao Cc: Andrew Morton , Linus Torvalds , Andi Kleen , Catalin Marinas , Dave Hansen , Hillf Danton , Jens Axboe , Jesse Barnes , Johannes Weiner , Jonathan Corbet , Matthew Wilcox , Mel Gorman , Michael Larabel , Rik van Riel , Will Deacon , Ying Huang , linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, page-reclaim@google.com, x86@kernel.org, Konstantin Kharlamov References: <20220104202227.2903605-1-yuzhao@google.com> <20220104202227.2903605-7-yuzhao@google.com> From: Vlastimil Babka In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: DA104100018 X-Stat-Signature: d6iw436wumnemmjphwfr4snfwm51aj8a Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=XXfMLcPM; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b="2W8/0bZv"; spf=pass (imf14.hostedemail.com: domain of vbabka@suse.cz designates 195.135.220.28 as permitted sender) smtp.mailfrom=vbabka@suse.cz; dmarc=none X-Rspamd-Server: rspam10 X-HE-Tag: 1641830469-617875 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: On 1/10/22 16:01, Michal Hocko wrote: > On Thu 06-01-22 17:12:18, Michal Hocko wrote: >> On Tue 04-01-22 13:22:25, Yu Zhao wrote: >> > +static struct lru_gen_mm_walk *alloc_mm_walk(void) >> > +{ >> > + if (!current->reclaim_state || !current->reclaim_state->mm_walk) >> > + return kvzalloc(sizeof(struct lru_gen_mm_walk), GFP_KERNEL); > > One thing I have overlooked completely. You cannot really use GFP_KERNEL > allocation here because the reclaim context can be constrained (e.g. > GFP_NOFS). This allocation will not do any reclaim as it is PF_MEMALLOC > but I suspect that the lockdep will complain anyway. > > Also kvmalloc is not really great here. a) vmalloc path is never > executed for small objects and b) we do not really want to make a > dependency between vmalloc and the reclaim (by vmalloc -> reclaim -> > vmalloc). > > Even if we rule out vmalloc and look at kmalloc alone. Is this really > safe? I do not see any recursion prevention in the SL.B code. Maybe this > just happens to work but the dependency should be really documented so > that future SL.B changes won't break the whole scheme. Slab implementations drop all locks before calling into page allocator (thus possibly reclaim) so slab itself should be fine and I don't expect it to change. But we could eventually reach the page allocator recursively again, that's true and not great.