From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-65.mta0.migadu.com [91.218.175.65]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1DBBC30D418 for ; Wed, 19 Aug 2026 05:38:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.65 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787117896; cv=none; b=qHnOWMceHh6Hu2NiybeWrjZshnqfiHPKhtlJ/MBLaetc4pDsbCpOjL/WV5uzHmsuf0vElSSOUUzlpDbkr2Vs7Ny7zP5/2L+9rsB6rNas69vDIneCAw2dMtO4a0dpDK9rdCADvUQg9Mf4EwXNBfXCFALAYj7KJrT1p+XpwWPeDkc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787117896; c=relaxed/simple; bh=tC9ZBjdlWTbI7P5V6dNNdQlq3npjUWVt+l2SpesYvG0=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=geRQRsPxlt+CXwstBDmNsReflRfaYGTnU3jcw8YAH/IDbndAAa6Xbt/eO44zcU93do3znhzUKPm/NE9xt6KQjMdU//wwQFzoUVqEZ1t37ICIh2E/TB2siGLMAZsM3qte09CaqrQW4zk5MQJMIAieEGJnmoZdbO6cQoPVSxRb198= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=QpkA5Fry; arc=none smtp.client-ip=91.218.175.65 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="QpkA5Fry" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=tC9ZBjdlWTbI7P5V6dNNdQlq3npjUWVt+l2SpesYvG0=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1787117890; v=1; x=1787722690; b=QpkA5FryOr2Bfia407kXSBjt31B3nXAPuHYMU/38Tl9ZUFROamapwACt84X7sqd5GzEbEgN6 FunSv1CzT5N8EdWgBZNtebPoSfEFXkEC9sE7IqVWZkBQQTaW0ZxWaLCddwf2XlEPFiUEhzTUDRj 5w0THr++fo0k7Iv8Z1xSyBpI= X-Envelope-To: linux-kernel@vger.kernel.org Received: from localhost (2602:fce1:44f:115e::) by smtp.migadu.com with ESMTPS id 1a377b22757d086f; 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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit +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