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Tue, 30 Apr 2024 13:07:05 +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 8XhyHPnsMGYzLAAAD6G6ig (envelope-from ); Tue, 30 Apr 2024 13:07:05 +0000 Date: Tue, 30 Apr 2024 15:07:04 +0200 From: Michal Hocko To: Pasha Tatashin Cc: lsf-pc@lists.linux-foundation.org, linux-mm Subject: Re: [Lsf-pc] [LSF/MM/BPF TOPIC] Dynamic Growth of Kernel Stacks Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Action: no action X-Rspamd-Server: rspam01 X-Stat-Signature: 1acky5q8hjr163fqafeb8fnuw81zrtor X-Rspam-User: X-Rspamd-Queue-Id: 61622A0027 X-HE-Tag: 1714482427-229791 X-HE-Meta: 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 tKEtF7mN bdRSrTGfxOQrw6wM/OcTzFSlQ/MAWvnWyDD6j4MQIIXNameE/rNPe6F9IafsnnmOXMPy6JuVuSpC6+6V2PhcIrpDYYmFz5XTnyqpCeerQZTPzY31cTPDXWlm8/6vH9VROGgtwnBPsve57Jn5Ge74wALq66CEnGy9pn0mjjgQTqS0eiwLaRAEBFCQDIvu0K2hJNxP4dgHKJcDpJRt/7RofsirDP4BkHYtgd1sI1OCdc/BZkGSTKjTvYxpiZ4wT1PKP9Kc4ikOKp4VHC2KIsJMiDb8Ug+lfHd91VMwv/RMs+wHRZ+mK/uYph5Uah/wRuzQssxeXCgdv+NJ5qyul81r+MCuW60kyGo9Kw9wSr02l9xMHs42nsXsRDfVSw8d45hc2FB9Shm1CY9TqCQY= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000007, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Pasha, is this something you still do consider interesting (and also productive in absence of x86 maintainers) to discuss at LSFMM? On Thu 22-02-24 20:03:37, Pavel Tatashin wrote: > For a long time, an 8K kernel stack was large enough. However, since > 2014, the default stack size has increased to 16K [1]. To conserve > memory at Google, we maintained 8K stacks via a custom patch while > verifying that our workload could fit within this limit. > > As we qualify new workloads and kernels, we find it more difficult to > keep the stacks at 8K. Therefore, we will increase the stack size to > the mainline value of 16K. However, this translates to a significant > increase in memory usage, potentially counted in petabytes. > > With virtually mapped stacks [2], it's possible to implement > auto-growth on faults. Ideally, the vast majority of kernel threads > could fit into 4K or 8K stacks, with only a small number requiring > deeper stacks that would expand as needed. > > The complication is that new pages must always be available from > within an interrupt context. To ensure this, pages must be accessible > to kernel threads in an atomic and lockless manner. This could be > achieved by using a per-CPU supply of pages dedicated to handling > kernel-stack faults. > > [1] https://lwn.net/Articles/600644 > [2] https://lwn.net/Articles/692608 > _______________________________________________ > Lsf-pc mailing list > Lsf-pc@lists.linux-foundation.org > https://lists.linuxfoundation.org/mailman/listinfo/lsf-pc -- Michal Hocko SUSE Labs