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X-IronPort-AV: E=McAfee;i="6500,9779,10647"; a="316686422" X-IronPort-AV: E=Sophos;i="5.98,254,1673942400"; d="scan'208";a="316686422" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Mar 2023 18:11:30 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6500,9779,10647"; a="742677381" X-IronPort-AV: E=Sophos;i="5.98,254,1673942400"; d="scan'208";a="742677381" Received: from yhuang6-desk2.sh.intel.com (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.238.208.55]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Mar 2023 18:11:26 -0700 From: "Huang, Ying" To: Chris Li Cc: Yosry Ahmed , lsf-pc@lists.linux-foundation.org, Johannes Weiner , Linux-MM , Michal Hocko , Shakeel Butt , David Rientjes , Hugh Dickins , Seth Jennings , Dan Streetman , Vitaly Wool , Yang Shi , Peter Xu , Minchan Kim , Andrew Morton , Aneesh Kumar K V , Michal Hocko , Wei Xu Subject: Re: [LSF/MM/BPF TOPIC] Swap Abstraction / Native Zswap References: <87356e850j.fsf@yhuang6-desk2.ccr.corp.intel.com> <87y1o571aa.fsf@yhuang6-desk2.ccr.corp.intel.com> Date: Mon, 13 Mar 2023 09:10:18 +0800 In-Reply-To: (Chris Li's message of "Fri, 10 Mar 2023 15:14:23 -0800") Message-ID: <87ttyp78xx.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 307E414000C X-Stat-Signature: 7dzj1pyt8gqpe8fhosxdzobxr9x8iq9n X-HE-Tag: 1678669892-936426 X-HE-Meta: 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 H3dvGq9I 8Jumv+x3mQD1WVDIxxeHJNN5hj8ckCyhGiLUM/72NdzZY1O10mO+WHIGv6hHmqLG0RmI5jOKseV8PE3isodSh9ykhg+RQbK1yEpFkWl34YetXxbRdztncCnkKIxbIi+TRHFiwsU9SLdooBIcoLnUk3Wwfm54x9v+3TMpxP2BpNTW3VViVf/YK9k0noX4uJeUqg/+dNjQM+J0bVtPU77yoiqXYcQGji6Kmg66a 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: Chris Li writes: > On Fri, Mar 10, 2023 at 11:06:37AM +0800, Huang, Ying wrote: >> > Unfortunately it's a little bit more. 24 is the extra overhead. >> > >> > Today we have an xarray entry for each swapped out page, that either >> > has the swapcache pointer or the shadow entry. >> > >> > With this implementation, we have an xarray entry for each swapped out >> > page, that has a pointer to the swap_desc. >> > >> > Ignoring the overhead of the xarray itself, we have (8 + 24) / (8 + 1) = 3.5556. >> >> OK. I see. We can only hold 8 bytes for each xarray entry. To save >> memory usage, we can allocate multiple swap_desc (e.g., 16) for each >> xarray entry. Then the memory usage of xarray becomes 1/N. > > The xarray look up key is the swap offset from the swap entry. If you > put more than one swap_desc under the one xarray entry. It will mean > all those different swap_descs will share a swap offset. For example, if we allocate 16 swap_desc for each xarray entry. Then, we can use (swap_desc_index >> 4) as key to lookup xarray, and (swap_desc_index & 0x15) to index inside 16 swap_desc for the xarray entry. Best Regards, Huang, Ying