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From: Shakeel Butt To: Suren Baghdasaryan Cc: Usama Arif , Andrew Morton , linux-mm@kvack.org, hannes@cmpxchg.org, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH] alloc_tag: introduce Kconfig option for default compressed profiling Message-ID: <72pac6pkjebt6xo7engiuuu7r3zr7fu6fh6bj77f22m7gslxgr@3gjawofplas2> References: <20250416180653.3438158-1-usamaarif642@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 90C37C0005 X-Rspam-User: X-Stat-Signature: otnqhfdter71ukh9uxq3st5nxjd6j5n4 X-HE-Tag: 1744839716-794793 X-HE-Meta: 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 ev+lRBNY FbLJs+5QWYG2BRQMAtGXbQ/L+HiLvNT9TanBdJpx/7Hn8pk+3h2qPiUbL49BHxwVOk03tpKnUKEs9/vSlwPkNPJ6NJQnpacw2wR44ce+SAVomQ+GpFKkyuJkWjx6W+DzJIXTD2F0RQcVrocUs0rzIECh6QoBjcWDPP2IgBnFfbLovJWCYqgDuozi2o3cbQogjF7pqhz5DHlDOrAJ44lvjpLEQLm5qq0AAqK/Kys69IUHuU3rPWdQlGIL2hNhNmYeXcyv9n3FXSliFWNKI+FbpCWCjag== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, 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, Apr 16, 2025 at 02:08:31PM -0700, Suren Baghdasaryan wrote: > On Wed, Apr 16, 2025 at 11:06 AM Usama Arif wrote: > > > > With this Kconfig option enabled, the kernel stores allocation tag references > > in the page flags by default. > > > > There are 2 reasons to introduce this: > > - As mentioned in [1], compressed tags dont have system memory overhead > > and much lower performance overhead. It would be preferrable to have this as > > the default option, and to be able to switch it at compile time. Another > > option is to just declare the static key as true by default? > > - As compressed option is the best one, it doesn't make sense to have to > > change both defconfig and command line options to enable memory > > allocation profiling. Changing commandline across a large number of services > > can result in signifcant work, which shouldn't be needed if the kernel > > defconfig needs to be changed anyways. > > The reason tag compression is not the default option is because it > works only if there are enough free bits in the page flags to store a > tag index. If you configure it to use page flags and your build does > not have enough free bits, the profiling will be disabled (see > alloc_tag_sec_init()). Is it possible to fail the build in that case i.e. check the page flags availability at build time?