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Thu, 19 Feb 2026 09:54:48 +0000 Message-ID: Date: Thu, 19 Feb 2026 10:54:48 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Content-Language: en-US To: lsf-pc , "linux-nvme@lists.infradead.org" , "linux-block@vger.kernel.org" , linux-mm@kvack.org From: Hannes Reinecke Subject: [LSF/MM/BPF TOPIC] Memory fragmentation with large block sizes Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Action: no action X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Spamd-Result: default: False [-4.51 / 50.00]; BAYES_HAM(-3.00)[99.99%]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; TO_DN_EQ_ADDR_SOME(0.00)[]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; TO_DN_SOME(0.00)[]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; 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X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org Hi all, I (together with the Czech Technical University) did some experiments trying to measure memory fragmentation with large block sizes. Testbed used was an nvme setup talking to a nvmet storage over the network. Doing so raised some challenges: - How do you _generate_ memory fragmentation? The MM subsystem is precisely geared up to avoid it, so you would need to come up with some idea how to defeat it. With the help from Willy I managed to come up with something, but I really would like to discuss what would be the best option here. - What is acceptable memory fragmentation? Are we good enough if the measured fragmentation does not grow during the test runs? - Do we have better visibility into memory fragmentation other than just reading /proc/buddyinfo? And, of course, I would like to present (and discuss) the results of the testruns done on 4k, 8k, and 16k blocksizes. Not sure if this should be a storage or MM topic; I'll let the lsf-pc decide. Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich