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[173.79.56.208]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-46a3eb17e6asm82050841cf.69.2024.12.27.11.09.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 27 Dec 2024 11:09:53 -0800 (PST) Date: Fri, 27 Dec 2024 14:09:50 -0500 From: Gregory Price To: "Huang, Ying" Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, nehagholkar@meta.com, abhishekd@meta.com, kernel-team@meta.com, david@redhat.com, nphamcs@gmail.com, akpm@linux-foundation.org, hannes@cmpxchg.org, kbusch@meta.com Subject: Re: [RFC v2 PATCH 0/5] Promotion of Unmapped Page Cache Folios. Message-ID: References: <20241210213744.2968-1-gourry@gourry.net> <87o715r4vn.fsf@DESKTOP-5N7EMDA> <87wmfsi47b.fsf@DESKTOP-5N7EMDA> <87v7v5g99x.fsf@DESKTOP-5N7EMDA> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: 4mgkzu6xeb41xgqyq3u386pfwxf6wgg5 X-Rspamd-Queue-Id: 0FFCCC0010 X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1735326575-333332 X-HE-Meta: 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 zL/NCktJ 9snB7+8E6Nm1NgS5BzA5MVJgqGqWBoP+KVoHCnxZPRwuCthHDhE8FirMZsj/JQYZwLrCzijN3mAXMFSIky9rKq+J40K6ATIfZNtbkl6p9tirbGRMSpqk/tmXEjnVLsrDOmDVfcAnme7MF6LrQ5yvAx98hyit0GYxMJD/bVz4GatRqcL6Wm2r/4KHIE9xXwUj+eNxk/g6m1aOOiHinPUd3cdfLnrhLFS+9eJZAxTLIa+z6sJ2q2ayH2/3WUjeeR4R59LYv8N7iQTD8CRbqAplT4ANFouo6HMtKcHuYG5wKpvwK7OW19eFrLSE6S3bIs40gleFWBT9A9XKh7AI= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000443, 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 Fri, Dec 27, 2024 at 10:40:36AM -0500, Gregory Price wrote: > > Can we measure the largest improvement? For example, run the benchmark > > with all file pages in DRAM and CXL.mem via numa binding, and compare. > > I can probably come up with something, will rework some stuff. > so I did as you suggested, I made a program that allocates a 16GB buffer, initializes it, them membinds itself to node1 before accessing the file to force it into pagecache, then i ran a bunch of tests. Completely unexpected result: ~25% overhead from an inexplicable source. baseline - no membind() ./test Read loop took 0.93 seconds drop caches ./test - w/ membind(1) just before file open Read loop took 1.16 seconds node 1 size: 262144 MB node 1 free: 245756 MB <- file confirmed in cache kill and relaunch without membind to avoid any funny business ./test Read loop took 1.16 seconds enable promotion Read loop took 3.37 seconds <- migration overhead ... snip ... Read loop took 1.17 seconds <- stabilizes here node 1 size: 262144 MB node 1 free: 262144 MB <- pagecache promoted Absolutely bizarre result: there is 0% CXL usage ocurring, but the overhead we originally measured is still present. This overhead persists even if i do the following - disable pagecache promotion - disable numa_balancing - offline CXL memory entirely This is actually pretty wild. I presume this must imply the folio flags are mucked up after migration and we're incurring a bunch of overhead on access for no reason. At the very least it doesn't appear to be an isolated folio issue: nr_isolated_anon 0 nr_isolated_file 0 I'll have to dig into this further, I wonder if this happens with mapped memory as well. ~Gregory