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Wed, 19 Aug 2026 05:38:10 +0000 X-Migadu-Flow: FLOW_OUT From: Lance Yang To: usama.arif@linux.dev Cc: akpm@linux-foundation.org, david@kernel.org, chrisl@kernel.org, kasong@tencent.com, ljs@kernel.org, ziy@nvidia.com, linux-mm@kvack.org, ying.huang@linux.alibaba.com, baoquan.he@linux.dev, willy@infradead.org, youngjun.park@lge.com, hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev, alex@ghiti.fr, kas@kernel.org, baohua@kernel.org, dev.jain@arm.com, baolin.wang@linux.alibaba.com, nico.pache@linux.dev, liam@infradead.org, ryan.roberts@arm.com, vbabka@kernel.org, linux-kernel@vger.kernel.org, nphamcs@gmail.com, shikemeng@huaweicloud.com, yosry@kernel.org, kernel-team@meta.com, linmiaohe@huawei.com, Lance Yang Subject: Re: [PATCH v6 06/12] mm: swap in PMD swap entries as whole THPs during swapoff Date: Wed, 19 Aug 2026 13:38:03 +0800 Message-Id: <20260819053803.15868-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: <20260818131202.494754-7-usama.arif@linux.dev> References: <20260818131202.494754-7-usama.arif@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 9DF35A0008 X-Rspamd-Server: rspam10 X-Rspam-User: X-Stat-Signature: mzhq7ntfwsabk1eq97jhaiknmsgqp5aq X-HE-Tag: 1787117893-919319 X-HE-Meta: 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 u+LoMWIs m/6XgNCBZyhEWIgyISZON2obm/aLzXlcR0bOB186jCI9m0OsXyr+BzYl4hhE6jb1TY8OdlQKlifCRe7KAo4dr0lEpOOzJIx/p3jsR+8EjNqANlWSrSj5A6T2io2N1GHMR3Z+YpBdCSlIa2Aui/KFyy2tHv0ILgt6Ep0o+kyCyvTTcM+S/YYAIIGL+EkVe9RuCnjmSl8tlgEWCrQxINCzydrhmgtwrIutp5xDNNIXaDfLOWY9MN05ksYjcAFcXwfTyZC5PpXcuTYuFHd2zz49Fz8rWbkUjQDveJm8O Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: +Cc Miaohe On Tue, Aug 18, 2026 at 06:09:47AM -0700, Usama Arif wrote: [...] >+#ifdef CONFIG_THP_SWAP >+/* >+ * unuse_pmd - Map a locked folio at PMD granularity during swapoff. >+ * >+ * The caller provides a locked, swapped-in folio. Returns 0 on success >+ * (PMD was mapped). Returns -EAGAIN if the swap cache folio no longer >+ * matches the entry or the PMD changed under the lock (try_to_unuse will >+ * rescan). Returns -EIO if the folio is not uptodate or contains a poisoned >+ * subpage; in that case the PMD is split so unuse_pte_range() can handle >+ * individual pages. >+ */ >+static int unuse_pmd(struct vm_area_struct *vma, pmd_t *pmd, >+ unsigned long addr, softleaf_t entry, >+ struct folio *folio) >+{ >+ struct mm_struct *mm = vma->vm_mm; >+ struct page *page; >+ pmd_t new_pmd, old_pmd; >+ spinlock_t *ptl; >+ rmap_t rmap_flags = RMAP_NONE; >+ bool exclusive; >+ >+ if (unlikely(!folio_matches_swap_entry(folio, entry))) >+ return -EAGAIN; >+ >+ if (unlikely(!folio_test_uptodate(folio))) { >+ /* Let PTE fallback reread each slot independently. */ >+ swap_cache_del_folio(folio); >+ __split_huge_pmd(vma, pmd, addr, false); >+ return -EIO; >+ } >+ >+ if (unlikely(folio_contain_hwpoisoned_page(folio))) { >+ /* Let PTE fallback isolate the poisoned subpages. */ >+ __split_huge_pmd(vma, pmd, addr, false); >+ return -EIO; >+ } Hmm ... can this miss a poisoned tail? memory_failure() sets PageHWPoison(p) before taking folio_lock(), but PG_has_hwpoisoned is only set later. Since unuse_pmd_entry() holds folio lock across this check, memory_failure() can be blocked on folio_lock() with a tail already poisoned, IIUC ... folio_contain_hwpoisoned_page() then sees neither a poisoned head nor PG_has_hwpoisoned, and set_pmd_at() maps that tail through a normal PMD. Note that unuse_pte() checks PageHWPoison(page) directly. Should we check each subpage here as well before installing the PMD? >+ >+ page = folio_page(folio, 0); >+ >+ ptl = pmd_lock(mm, pmd); >+ old_pmd = pmdp_get(pmd); >+ >+ if (!pmd_is_swap_entry(old_pmd) || >+ softleaf_from_pmd(old_pmd).val != entry.val) { >+ spin_unlock(ptl); >+ return -EAGAIN; >+ } >+ >+ exclusive = pmd_swp_exclusive(old_pmd); >+ >+ /* >+ * Some architectures may have to restore extra metadata to the folio >+ * when reading from swap. This metadata may be indexed by swap entry >+ * so this must be called before folio_put_swap(). >+ */ >+ arch_swap_restore(folio_swap(entry, folio), folio); >+ >+ add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR); >+ add_mm_counter(mm, MM_SWAPENTS, -HPAGE_PMD_NR); >+ >+ new_pmd = folio_mk_pmd(folio, vma->vm_page_prot); >+ new_pmd = pmd_mkold(new_pmd); >+ if (pmd_swp_soft_dirty(old_pmd)) >+ new_pmd = pmd_mksoft_dirty(new_pmd); >+ if (pmd_swp_uffd(old_pmd)) >+ new_pmd = pmd_mkuffd(new_pmd); >+ if (pmd_swp_uffd(old_pmd) && userfaultfd_rwp(vma)) >+ new_pmd = pmd_modify(new_pmd, PAGE_NONE); >+ >+ if (exclusive) >+ rmap_flags |= RMAP_EXCLUSIVE; >+ >+ folio_get(folio); >+ if (!folio_test_anon(folio)) >+ folio_add_new_anon_rmap(folio, vma, addr, rmap_flags); >+ else >+ folio_add_anon_rmap_pmd(folio, page, vma, addr, rmap_flags); >+ >+ set_pmd_at(mm, addr, pmd, new_pmd); >+ folio_put_swap(folio, NULL); >+ >+ spin_unlock(ptl); >+ >+ folio_free_swap(folio); >+ return 0; >+} [...] Cheers, Lance