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Server (TLS) id 15.0.1497.48; Tue, 7 Jan 2025 12:29:31 +0000 Date: Tue, 7 Jan 2025 13:29:31 +0100 From: Daniel Gomez To: David Hildenbrand CC: Ryan Roberts , Barry Song , Andrew Morton , , Luis Chamberlain , Pankaj Raghav , Subject: Re: Swap Min Odrer Message-ID: <20250107122931.qpkn43yvs4kq3twi@AALNPWDAGOMEZ1.aal.scsc.local> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: X-Originating-IP: [106.110.32.87] X-ClientProxiedBy: CAMSVWEXC01.scsc.local (2002:6a01:e347::6a01:e347) To CAMSVWEXC01.scsc.local (2002:6a01:e347::6a01:e347) X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFprKKsWRmVeSWpSXmKPExsWy7djP87o6crXpBl/b5S3mrF/DZtH04BGT xdf1v5gt7q35z2pxY8JTRoue3VMZLXbc7WVzYPdYM28No8emVZ1sHps+TWL3ODHjN4vHu1lK Hu/3XWULYIvisklJzcksSy3St0vgylj19wNLwXaBiu/nuRsY3/F0MXJySAiYSNza/pe5i5GL Q0hgBaPEmykXmSCcL4wSz6+cZYFwPjNKTPs7iwmmZdPEX+wQieWMEn2rlzDCVX2Z/ZoNwtnM KPHv4CNmkBYWARWJN+dWsIHYbAKaEvtObmIHsUUENCQ2tW0A284M0v1r1X5WkISwgLREy6kT 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20250107122932eucas1p2a15e30f7e06ec883300c3e7393b0615b X-Msg-Generator: CA X-RootMTR: 20250107094349eucas1p1c973738624046458bbd8ca980cf6fe33 X-EPHeader: CA CMS-TYPE: 201P X-CMS-RootMailID: 20250107094349eucas1p1c973738624046458bbd8ca980cf6fe33 References: <20250107094347.l37isnk3w2nmpx2i@AALNPWDAGOMEZ1.aal.scsc.local> X-Rspamd-Queue-Id: 3650B140002 X-Rspamd-Server: rspam12 X-Stat-Signature: femk8ejh3dwpz58wfdct1qum843tns3z X-Rspam-User: X-HE-Tag: 1736252974-997192 X-HE-Meta: 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 Fr70leX4 GKG/qZnWzrNqdbxve49Z3hHyxhJt/PDttaybwMuT2zDbD/giHcodRSo1n+offFc1Gto1aZEf/5bZC1QkLYoED9TTX/nEBW9DWCH+4AjEamvOovdFuTjFwYCwA8Nqtd1YyS1jIsxAPXtwrp/C1bswJV4ZCe2aN1jvL1Q0awhTFLi27QOyEDj6AyZ2OZ46HN9Kg6hfQsL9iIKuymrw= 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: On Tue, Jan 07, 2025 at 11:31:05AM +0100, David Hildenbrand wrote: > On 07.01.25 10:43, Daniel Gomez wrote: > > Hi, > > Hi, > > > > > High-capacity SSDs require writes to be aligned with the drive's > > indirection unit (IU), which is typically >4 KiB, to avoid RMW. To > > support swap on these devices, we need to ensure that writes do not > > cross IU boundaries. So, I think this may require increasing the minimum > > allocation size for swap users. > > How would we handle swapout/swapin when we have smaller pages (just imagine > someone does a mmap(4KiB))? Swapout would require to be aligned to the IU. An mmap of 4 KiB would have to perform an IU KiB write, e.g. 16 KiB or 32 KiB, to avoid any potential RMW penalty. So, I think aligning the mmap allocation to the IU would guarantee a write of the required granularity and alignment. But let's also look at your suggestion below with swapcache. Swapin can still be performed at LBA format levels (e.g. 4 KiB) without the same write penalty implications, and only affecting performance if I/Os are not conformant to these boundaries. So, reading at IU boundaries is preferred to get optimal performance, not a 'requirement'. > > Could this be something that gets abstracted/handled by the swap > implementation? (i.e., multiple small folios get added to the swapcache but > get written out / read in as a single unit?). Do you mean merging like in the block layer? I'm not entirely sure if this could guarantee deterministically the I/O boundaries the same way it does min order large folio allocations in the page cache. But I guess is worth exploring as optimization. > > I recall that we have been talking about a better swap abstraction for years > :) Adding Chris Li to the cc list in case he has more input. > > Might be a good topic for LSF/MM (might or might not be a better place than > the MM alignment session). Both options work for me. LSF/MM is in 12 weeks so, having a previous session would be great. Daniel > > -- > Cheers, > > David / dhildenb >