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Wysocki (Intel)" Subject: Re: [PATCH v5 14/19] mm, swap: cleanup swap entry management workflow Date: Thu, 29 Jan 2026 11:32:38 -0800 Message-ID: <20260129200604.2518109-1-clm@meta.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20251220-swap-table-p2-v5-14-8862a265a033@tencent.com> References: <20251220-swap-table-p2-v5-0-8862a265a033@tencent.com> <20251220-swap-table-p2-v5-14-8862a265a033@tencent.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-Originating-IP: [2620:10d:c085:108::4] X-Proofpoint-GUID: xF3qSoIDUEYo5SoFh-hYPuqEGaxNgAIv X-Proofpoint-ORIG-GUID: xF3qSoIDUEYo5SoFh-hYPuqEGaxNgAIv X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMTI5MDE0NCBTYWx0ZWRfX/jxPxco3ghaj CyMdkkqj2tKEUBAmFy8D7iicZr2M0Vhpp2OVVukhEHHhmh58CEL672Ds+hZbvPDNt6h7ZL+amDB lLyNARogeomdtORE/XTf5mKyDNskPRf67Lvs3hyzCT/KPHC/uiNvvYkvau8QloluYaZeH/rQjQw tJEj6Nbswcz2FGYesLWarRkhFju7g61LaYdIcJhC3/YY44E/NjAbWCdCRJvSoCAfLMk5C3tf4W3 fYiOMTi4eIbsOxiv3w/7YuuqMLdpsQNCVmSh0Sbcb6MxRebRmqekwKdfrITnewO2eYaIqy+dvtS O2tjyIQrN8HoeSKIaDa1d7Jd6ad7H48YUKu797UXRDS0+FUdHsEr4KXMrJcLC20PJF4UrgFy8vz 4/sXOINoqOMwS/hhyuPp3p2/HGYSbJQDLHSbYO5CwQR86Lf+dpYhbOW3vQk7MyPFvuSOclhty3D 7LbT/O4WylZGAqG/42A== X-Authority-Analysis: v=2.4 cv=U72fzOru c=1 sm=1 tr=0 ts=697bbdc2 cx=c_pps a=CB4LiSf2rd0gKozIdrpkBw==:117 a=CB4LiSf2rd0gKozIdrpkBw==:17 a=vUbySO9Y5rIA:10 a=VkNPw1HP01LnGYTKEx00:22 a=pGLkceISAAAA:8 a=GvQkQWPkAAAA:8 a=PyCarBDI3Nz51ks_hl0A:9 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-01-29_03,2026-01-29_01,2025-10-01_01 X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 592891A0005 X-Stat-Signature: sahkb7iykguqc7bfh81rnkq55msdjwu3 X-HE-Tag: 1769717217-156183 X-HE-Meta: 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 Wi8V48Gj djtekU5/ddZH5phXLld6Wk2g98nlWSVXuotyGjjY7onHEM6PzSARuXlHcKbzvcazup3N+MGgPAPm9t0uSyi50xu9zbaBBDVi6drwjr+D5YuBDf+AxDka2HpaWOxF/GJyiIadcTWgxjjQ3bLlnlTJlefNTtreRABmvJuPUoG8DybyRlG4vvz6pMojHvbOUgeJasT+UChVrdgswM11xKWN/rvNS48+3zylTqFzE+njvAic4nBHXt9/f2opfEwUVFrDCTT6eVwdSoD61tD/9L4gx/NgyjF+eSe8+WNlJr83aRgEhHM+HxtnvTmdbiCXMPSYwmqVAIriO1UCVM1Av30lzMxyhxxKtJLToUDnqPxAkVLUMWuGrLcVf09PlZJ7Kb677Jmyy 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: Kairui Song wrote: > From: Kairui Song > > The current swap entry allocation/freeing workflow has never had a clear > definition. This makes it hard to debug or add new optimizations. > > This commit introduces a proper definition of how swap entries would be > allocated and freed. Now, most operations are folio based, so they will > never exceed one swap cluster, and we now have a cleaner border between > swap and the rest of mm, making it much easier to follow and debug, > especially with new added sanity checks. Also making more optimization > possible. > > Swap entry will be mostly allocated and free with a folio bound. > The folio lock will be useful for resolving many swap ralated races. > > Now swap allocation (except hibernation) always starts with a folio in > the swap cache, and gets duped/freed protected by the folio lock: [ ... ] Hi everyone, Apologies for looping back around on this one, but I've got some prompt changes that break down larger commits into sections and run them independently through review. I reran it on mm-new, and it found something new: > diff --git a/mm/swapfile.c b/mm/swapfile.c > index 64970ee11fcf7..85bf4f7d9ae7b 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c [ ... ] > @@ -2195,7 +2265,7 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd, > /* > * Some architectures may have to restore extra metadata to the page > * when reading from swap. This metadata may be indexed by swap entry > - * so this must be called before swap_free(). > + * so this must be called before folio_put_swap(). > */ > arch_swap_restore(folio_swap(entry, folio), folio); > > @@ -2236,7 +2306,7 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd, > new_pte = pte_mkuffd_wp(new_pte); > setpte: > set_pte_at(vma->vm_mm, addr, pte, new_pte); > - swap_free(entry); > + folio_put_swap(folio, page); Does this corrupt the swap map when ksm_might_need_to_copy() returns a new folio? In that case, folio != swapcache, and the new folio is NOT in the swap cache with folio->swap = 0. This would trigger VM_WARN_ON_FOLIO(!folio_test_swapcache(folio), folio) and call swap_entries_put_map() with entry.val = 0. Compare with do_swap_page() which correctly uses folio_put_swap(swapcache, NULL) when folio != swapcache. Should this use the original entry parameter or the swapcache folio instead?