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smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=GJPwlCXx; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9F6B6607E802 for ; Fri, 13 Nov 2026 17:39:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=GJPwlCXx Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1E1BF1F000C6; Fri, 13 Nov 2026 17:39:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794591566; bh=dm8q8HGPHE9E98Lt4CJ5Z1tUerEAxjiOuXmAiX4bR3k=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=GJPwlCXxg4dqojQf5ueDh9IrlaSbGZO0JTmYaJQfn9oeW6hwuzQ31647nd+eCdAiM c3dP0I8334riJdJpI663KprFneiBckFlSv7YhbNtuQF6t2UIGX+lRxL0DEuo7nifWU vHQ2PPNUguiOeFgNd5Jhe84QJCoy6nHyL3oR6c9vLooCa2mdAkYaH6sSonUszYpdhO mRkEnd4xpyXmdf8iWU66G1xdatv9n5GVbNGEKIWVoVW+PBR8YB2wjESBvfVHfDIKyA 8394hibUzO+kInePRReL0tZCB04bhVYUX09nnmgo7JiPg9OJAFJfY7zQyh7t/bp1d6 j5dP7ZKfGKvMQ== Message-ID: <16bb1a14-04f4-4524-9882-20d452175a3d@kernel.org> Date: Fri, 13 Nov 2026 18:39:20 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: synchronize with PTE table reclaim for all folio sizes To: Baolin Wang , akpm@linux-foundation.org, ljs@kernel.org Cc: riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, lance.yang@linux.dev, qi.zheng@linux.dev, pfalcato@suse.de, ayushr@modal.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/5/26 03:56, Baolin Wang wrote: > Similar to commit 243cf1f67b36 ("mm: memory: fix truncation removing mapped > folios"), the '!pmd_present()' check in page_vma_mapped_walk() can also race > with concurrent page table reclamation via zap_empty_pte_table(). > > page_vma_mapped_walk() is used by many functions including try_to_unmap(), > try_to_migrate(), folio_mkclean(), pfn_mkclean_range(), remove_migration_ptes(), > page_mapped_in_vma(), and mapping_wrprotect_range(). Except for try_to_unmap() > and try_to_migrate(), the other callers do not perform post-walk accounting > checks, so the race has no observable impact on them. > > For migration, the race can cause unnecessary retries. For reclaim via > try_to_unmap(), the race can cause failure to reclaim a folio that is in > fact already unmapped (as shown below), which may lead to unexpected OOM > or increased refaults. > > CPU 0 (reclaim) CPU 1 (MADV_DONTNEED) > -------------------------------- -------------------------------- > folio_lock(F) > try_to_unmap(F, TTU_SYNC) > zap_pte_range(full PMD range) > spin_lock(ptl) > clear PTEs > zap_empty_pte_table() > spin_trylock(pml) > pmd_clear() > spin_unlock(pml) > > page_vma_mapped_walk() > observe !pmd_present(pmde) > nr_pages < HPAGE_PMD_NR > skip synchronization > return false > > try_to_unmap() returns > folio_mapped(F) == true > nr_unmap_fail += folio_nr_pages(F) > tlb_flush_mmu_tlbonly() > tlb_flush_rmaps() > remove F's rmaps > spin_unlock(ptl) > > Commit 243cf1f67b36 ("mm: memory: fix truncation removing mapped folios") > has already moved the PMD clear operation (via zap_empty_pte_table()) to > after tlb_flush_rmaps(). Similarly, page_vma_mapped_walk() also needs to > use sync_with_folio_pmd_zap() to synchronize and avoid memory ordering > issues on weakly ordered CPUs. > > Fixes: 6375e95f381e ("mm: pgtable: reclaim empty PTE page in madvise(MADV_DONTNEED)") > Cc: stable@vger.kernel.org > Suggested-by: David Hildenbrand (Arm) > Signed-off-by: Baolin Wang > --- > mm/page_vma_mapped.c | 5 +---- > 1 file changed, 1 insertion(+), 4 deletions(-) > > diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c > index e6b6170c2f4f..8797467b6f0c 100644 > --- a/mm/page_vma_mapped.c > +++ b/mm/page_vma_mapped.c > @@ -293,10 +293,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > spin_unlock(pvmw->ptl); > pvmw->ptl = NULL; > } else if (!pmd_present(pmde)) { > - if ((pvmw->flags & PVMW_SYNC) && > - thp_vma_suitable_order(vma, pvmw->address, > - PMD_ORDER) && > - (pvmw->nr_pages >= HPAGE_PMD_NR)) > + if (pvmw->flags & PVMW_SYNC) > sync_with_folio_pmd_zap(mm, pvmw->pmd); > > goto next_pmd; Baolin, how to proceed with that? Are you intending a resend? Including some of the performance impact and ways forward to optimize? -- Cheers, David