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X-CSE-ConnectionGUID: Cj0dsUDlT46+fQUlotmN0Q== X-CSE-MsgGUID: vThzNPAlRci3t4uPVn1y/A== X-IronPort-AV: E=McAfee;i="6700,10204,11103"; a="15389989" X-IronPort-AV: E=Sophos;i="6.08,238,1712646000"; d="scan'208";a="15389989" Received: from orviesa004.jf.intel.com ([10.64.159.144]) by orvoesa109.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Jun 2024 07:45:38 -0700 X-CSE-ConnectionGUID: Rlxw343pRhedGyMyue1lYQ== X-CSE-MsgGUID: XWMDZ4yQRcSuekhmgcgEHw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.08,238,1712646000"; d="scan'208";a="45636124" Received: from tassilo.jf.intel.com (HELO tassilo.localdomain) ([10.54.38.190]) by orviesa004.jf.intel.com with ESMTP; 14 Jun 2024 07:45:38 -0700 Received: by tassilo.localdomain (Postfix, from userid 1000) id 365123057C6; Fri, 14 Jun 2024 07:45:37 -0700 (PDT) From: Andi Kleen To: Usama Arif Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, shakeel.butt@linux.dev, david@redhat.com, ying.huang@intel.com, hughd@google.com, willy@infradead.org, yosryahmed@google.com, nphamcs@gmail.com, chengming.zhou@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH v5 1/2] mm: store zero pages to be swapped out in a bitmap In-Reply-To: <20240614100902.3469724-2-usamaarif642@gmail.com> (Usama Arif's message of "Fri, 14 Jun 2024 11:07:05 +0100") References: <20240614100902.3469724-1-usamaarif642@gmail.com> <20240614100902.3469724-2-usamaarif642@gmail.com> Date: Fri, 14 Jun 2024 07:45:37 -0700 Message-ID: <87ed8zmvla.fsf@linux.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Queue-Id: 30A10180008 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: bxrfckdee4py11t819e6wtiyn3pzpjph X-HE-Tag: 1718376338-6382 X-HE-Meta: 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 z8EuByUY FHz8cuuenWKC/FJkp+BkdZnsqKL970okgJ4Du3wHx6tI5S66nEalqdzCh/DTuV3BF/jFB4V+0u7qW2hJhs9q9EeJi/eF86881mi0gaXXG784fPffTmS6YyBDDGC3vCTis3HFlAaA5slODjr1gUmSSNEa05WrO+rbaZQMp 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: Usama Arif writes: > Approximately 10-20% of pages to be swapped out are zero pages [1]. > Rather than reading/writing these pages to flash resulting > in increased I/O and flash wear, a bitmap can be used to mark these > pages as zero at write time, and the pages can be filled at > read time if the bit corresponding to the page is set. > With this patch, NVMe writes in Meta server fleet decreased > by almost 10% with conventional swap setup (zswap disabled). > > [1] https://lore.kernel.org/all/20171018104832epcms5p1b2232e2236258de3d03d1344dde9fce0@epcms5p1/ But how much did the CPU time increase? Surely the new loop is not free? -Andi