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Wed, 19 Jun 2024 10:57:19 -0700 (PDT) MIME-Version: 1.0 References: <20240618093656.1944210-1-takayas@chromium.org> <20240618155320.75807db5@rorschach.local.home> In-Reply-To: <20240618155320.75807db5@rorschach.local.home> From: Takaya Saeki Date: Thu, 20 Jun 2024 02:57:08 +0900 Message-ID: Subject: Re: [PATCH] filemap: add trace events for get_pages, map_pages, and fault To: Steven Rostedt Cc: Matthew Wilcox , Andrew Morton , Masami Hiramatsu , Mathieu Desnoyers , Junichi Uekawa , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 736BAA0017 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: fkdya7s16z57k1mi7ceu567463fq3iby X-HE-Tag: 1718819841-183771 X-HE-Meta: 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 aLvI2B7R 2mPQM5dAg6qmrjgY7LWSWlaNtxMQTZ/knspg+uhLysFsO/GkeB4V8P3KrXEqwY12TOxdx4jWiQzWGvPfuwCcIfqwkNuROTaYdC2J0qjJUtqcdItl6DeGFv1AJXvsOP+zX31msyieXWbrpO4jycKdNEXUXbhiiAMoXfq6e2dCQ6E+C8e1RmcvogxYkmNvnfKhEerermPcAqejfo/vWKxC6KXZshA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.009239, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Thanks Steven for trying it out. > I can see it bringing down the number of pages needed to be saved dramatically. Yes, I agree. However, note that wc does not count the size of the page caches correctly since 'get_map_pages' gives you a range. In your example of the less command, actually the total sizes of page_cache_size and get_map_pages look the same. Instead of less, running a large binary such as Chrome (232MB) gives us a better example. '# trace-cmd record -e filemap chrome --version' showed 58% reduction from 42MB to 17MB in my environment. - Total size of mm_filemap_add_to_page_cache: 42,958,848 bytes - With mm_filemap_map_pages and mm_filemap_get_pages: 17,993,728 bytes By the way, 'mm_filemap_map_pages' traces a range requested to populate, which includes pages that are not in caches yet and thus are skipped. So, you need to calculate the intersection with mm_filemap_add_to_page_cache to see page caches that are actually mapped. I'm wondering if we should put a trace event per each successful page mapping event as mm_filemap_add_to_page_cache does, by putting an event inside the page map loop.