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From: Shakeel Butt To: Pasha Tatashin Cc: akpm@linux-foundation.org, jpoimboe@kernel.org, kent.overstreet@linux.dev, peterz@infradead.org, nphamcs@gmail.com, cerasuolodomenico@gmail.com, surenb@google.com, lizhijian@fujitsu.com, willy@infradead.org, vbabka@suse.cz, ziy@nvidia.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v5 2/3] vmstat: Kernel stack usage histogram Message-ID: References: <20240724203322.2765486-1-pasha.tatashin@soleen.com> <20240724203322.2765486-3-pasha.tatashin@soleen.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240724203322.2765486-3-pasha.tatashin@soleen.com> X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 27E3120021 X-Stat-Signature: mz3gbdr676hxcue6zxpywerw6nogxd7j X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1721854161-645900 X-HE-Meta: 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 p60stHLF rQBfAMelBF5xAb1y/j7XdkxNdUujKZYQ0ZfwA6K9u8AVZinr3ixH3tLfYOzaSWw5Srb7gUWXLXyj3knebCRR5N7RBE6XOCw2Mk3MC6IeaeI1q0aicj5WKeQSe8t2P3trToHWX4j/Hs04vwVnj2vUkoHTP/uhTnCzL2QwOZ5X3U+P5TO/41D923bl74MqZUSvL/gsvd0HK2Uqb8dMZLR9GE4IECsuu2BJ2b+7lfTxaQa5Vv3BrKUAJQb7IWg== 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 Wed, Jul 24, 2024 at 08:33:21PM GMT, Pasha Tatashin wrote: > As part of the dynamic kernel stack project, we need to know the amount > of data that can be saved by reducing the default kernel stack size [1]. > > Provide a kernel stack usage histogram to aid in optimizing kernel stack > sizes and minimizing memory waste in large-scale environments. The > histogram divides stack usage into power-of-two buckets and reports the > results in /proc/vmstat. This information is especially valuable in > environments with millions of machines, where even small optimizations > can have a significant impact. > > The histogram data is presented in /proc/vmstat with entries like > "kstack_1k", "kstack_2k", and so on, indicating the number of threads > that exited with stack usage falling within each respective bucket. > > Example outputs: > Intel: > $ grep kstack /proc/vmstat > kstack_1k 3 > kstack_2k 188 > kstack_4k 11391 > kstack_8k 243 > kstack_16k 0 > > ARM with 64K page_size: > $ grep kstack /proc/vmstat > kstack_1k 1 > kstack_2k 340 > kstack_4k 25212 > kstack_8k 1659 > kstack_16k 0 > kstack_32k 0 > kstack_64k 0 > > Note: once the dynamic kernel stack is implemented it will depend on the > implementation the usability of this feature: On hardware that supports > faults on kernel stacks, we will have other metrics that show the total > number of pages allocated for stacks. On hardware where faults are not > supported, we will most likely have some optimization where only some > threads are extended, and for those, these metrics will still be very > useful. > > [1] https://lwn.net/Articles/974367 > > Signed-off-by: Pasha Tatashin > Reviewed-by: Kent Overstreet Acked-by: Shakeel Butt