From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=95.215.58.216 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793854455; b=etYON6czh64GqNlh7rdRdLEx5PALwqfT1aK6waJ85b1eg5/hCdK2ojR6PuCGpQqe7o0A g93XgOFIhQrqlmYuGlQtxgVIPdD1+o3cj0ebixKHkXPNBKRgRaUlnVv0qoMghoz6+zdtt wHlCsEHvMjlb2XCMrkq8UndpHNufsPdCeElwSVi6zZerSRhBXL49fOZd82iE2dS5rubv5 uNH0syzp1zWvSRFvILlw1WrB9iv/ETLMTOEeA/0feAJKp6IStA9kqEeXmqez83KpAXsnq 4zz+AjRuzxKP1itrgeU70sZjbXT69g/i/tUrLMKf+3PLeNpZd1/y6TanfDqM7Dn719g== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793854455; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:From:To:Cc:Subject:Date:Message-ID: X-Mailer:In-Reply-To:References:MIME-Version:Content-Type: Content-Transfer-Encoding; bh=SOnxtD5kQgW2tF7PVrffOT/lerqKVdwMhcbBwPAH/FM=; b=14HSymAJw/zOofsGm8DNtmDe5VbDHl5AURzb32HpGiBBXKzEtqCcznGHjJ9eQMw6uDZa iWh7MqweF7OWNo+qJVXouDgVtOK4oK0ZBYt8nMMkDq3GyNe1EsDte0yubhj5+m10t+hda OlZV3cvXjCG/mEED4MAnnt5Qq7bcAqsc6LXhwD06qtnTMrdgjezWba6yy18D/9RNXOeuy +4zwOJkk0Hhizrf61CdO7eYo3V7jtBeSieoDfntRCwqwrPGSMIzh07TGrb8+pR/Oqko31 TKaUHMTOCewNH860aTbQ7d1xQjgJQJprExxh7+Myu/UOdqsPL51lzxMJFgN40mvMDhA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=R8+KcAAw; arc=none smtp.remote-ip=95.215.58.216 Received: from mta1.migadu.com (out-216.mta1.migadu.com [95.215.58.216]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4EB6F606A328 for ; Thu, 5 Nov 2026 04:54:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 4EB6F606A328 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, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=R8+KcAAw X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=qIbdiMjLr9Y0SUefhfkdE51Knh5aRfQ/kBIeoszyPGg=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793854452; v=1; x=1794459252; b=R8+KcAAwP5th3uxXwZF0lIDf5ASxqNS9DWJPnfcXG0mVIzDVJyDNOzlkeiRYDx7qxjDcFf9K /Ko7fmQstorud3tguEysoSZ2htTJ+IeZMRmSfmx9JBGDfUo3xxYWjopCwmZqiMtGccOcV4IfTo2 0MDpnF9TRoQsBPnAp+htccyE= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id f63fd72cc0f28980; Thu, 05 Nov 2026 04:54:11 +0000 X-Mizu-Trace-ID: f63fd72cc0f28980 X-Migadu-Flow: FLOW_OUT From: Lance Yang To: baolin.wang@linux.alibaba.com Cc: akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, 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 Subject: Re: [PATCH] mm: synchronize with PTE table reclaim for all folio sizes Date: Thu, 5 Nov 2026 12:54:06 +0800 Message-ID: <20261105045406.39871-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: References: 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 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On Thu, Nov 05, 2026 at 10:56:28AM +0800, 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(). Good catch! >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) Right. Whether the folio can be PMD-mapped doesn't tell us whether its PTE table can be reclaimed, so those extra checks can skip synchronization that the caller explicitly asked for ;) LGTM, thanks! Reviewed-by: Lance Yang > sync_with_folio_pmd_zap(mm, pvmw->pmd); > > goto next_pmd; >-- >2.47.3 > >