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allocation tag refs in page flags To: Yosry Ahmed , Suren Baghdasaryan Cc: akpm@linux-foundation.org, kent.overstreet@linux.dev, corbet@lwn.net, arnd@arndb.de, mcgrof@kernel.org, rppt@kernel.org, paulmck@kernel.org, thuth@redhat.com, tglx@linutronix.de, bp@alien8.de, xiongwei.song@windriver.com, ardb@kernel.org, david@redhat.com, vbabka@suse.cz, mhocko@suse.com, hannes@cmpxchg.org, roman.gushchin@linux.dev, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, pasha.tatashin@soleen.com, souravpanda@google.com, keescook@chromium.org, dennis@kernel.org, yuzhao@google.com, vvvvvv@google.com, rostedt@goodmis.org, iamjoonsoo.kim@lge.com, rientjes@google.com, minchan@google.com, kaleshsingh@google.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-modules@vger.kernel.org, kernel-team@android.com References: <20241014203646.1952505-1-surenb@google.com> <20241014203646.1952505-6-surenb@google.com> Content-Language: 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 bqL/UgCx 1uDLOzLlW5WuIpMoIjR3qHANru3kFc70SQKrvpBXUZXHIEykR3EJ6h3uUC8hvImHPnEpkVIR4t+9qOg28K1PL4uhcBPNZMsO1ao9Ar2lw+sx4Mlc0tRE90HqQ1DKHUmjmOJdSScbd+Hdcd9OcT7j9YYcLpzNin4wag7i6QZnwSdzgZIYgeaHzZPRypR0N+yM1PnjMP1thOQ3Rtv4sru+UNCmJpO60MlNCdhKxWhHimg9vg+xuICRE3y/uU0qTnY2ZxC0JTXWvmJeCPGbrab65+xgcPNZpHe5M/hRiq+W51JLpH8a6D98z+b5o2sh14/5weeSBoZgVf08pDpElu922CgF6D78H9moACffnXb3lecJ32N0PjLo5NUv+lgw87+KVc+g0kNj4Am5jVOFphYOMu9A43MsPaJeJmUK9 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 10/14/24 4:48 PM, Yosry Ahmed wrote: > On Mon, Oct 14, 2024 at 1:37 PM Suren Baghdasaryan wrote: >> >> Add CONFIG_PGALLOC_TAG_USE_PAGEFLAGS to store allocation tag >> references directly in the page flags. This eliminates memory >> overhead caused by page_ext and results in better performance >> for page allocations. >> If the number of available page flag bits is insufficient to >> address all kernel allocations, profiling falls back to using >> page extensions with an appropriate warning to disable this >> config. >> If dynamically loaded modules add enough tags that they can't >> be addressed anymore with available page flag bits, memory >> profiling gets disabled and a warning is issued. > > Just curious, why do we need a config option? If there are enough bits > in page flags, why not use them automatically or fallback to page_ext > otherwise? Or better yet, *always* fall back to page_ext, thus leaving the scarce and valuable page flags available for other features? Sorry Suren, to keep coming back to this suggestion, I know I'm driving you crazy here! But I just keep thinking it through and failing to see why this feature deserves to consume so many page flags. thanks, -- John Hubbard > > Is the reason that dynamically loadable modules, where the user may > know in advance that the page flags won't be enough with the modules > loaded?