From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-113.freemail.mail.aliyun.com (out30-113.freemail.mail.aliyun.com [115.124.30.113]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 32171257821 for ; Mon, 20 Oct 2025 11:00:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.113 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760958044; cv=none; b=KOQtZtgnFdUmdzItkkIbHBtOsxsm0gbz5/NquxH5sptHbmw6lwc4A83LJJ4L3ydGlElRogV5eADdZGLSDUOYA2up/y21q2G4x4jUZGgzkXi0ZgrCNtDnDTdqiVZZ8aSiFymVQZAktxYcenrDfBZL3S4IGLPBMM+6cNKuydttfdw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760958044; c=relaxed/simple; bh=dTxv6HYgb1ZLq67JkWsfuo5X7sQIs7lbyB+Bz24Brcs=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=tsWlOsAYAdlFfC6PmKKS9gPpEuxWdHPAZEegQcmwcywOrm1VTE+TmqmtYJuB+YNwqIt9EpJuM1TJSgde+/dCeQkCFTvHX2jUlc70q2pSRVdlNXe2mJ49iQwW6q9FpMilH920zIAjPGc48lJgUYkssKPkkYurrYaRlKFAIQEuPvY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=vKCILETA; arc=none smtp.client-ip=115.124.30.113 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="vKCILETA" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1760958031; h=From:To:Subject:Date:Message-ID:MIME-Version:Content-Type; bh=I0Rh7vr2r5CUO65seAlIgLtsprqiSEsZXpmW27HKpY8=; b=vKCILETAQIAXB2mymeoWIkyPmi6VFBcARRmvQ97utVLqA4cRvQZIegoj8j17XnmBiy6Y9HKCEvYMs/W8PnTdeSX0JvFG5ePY+KUPECGSYo8pkf0GeQwRlhv6zvFFerJb8ejXWI428BKDDzrcfCuF+VZOQt+UvXKFweGEFd0XovI= Received: from DESKTOP-5N7EMDA(mailfrom:ying.huang@linux.alibaba.com fp:SMTPD_---0WqbBPTq_1760958022 cluster:ay36) by smtp.aliyun-inc.com; Mon, 20 Oct 2025 19:00:30 +0800 From: "Huang, Ying" To: Catalin Marinas Cc: Will Deacon , Anshuman Khandual , Ryan Roberts , Gavin Shan , Ard Biesheuvel , "Matthew Wilcox (Oracle)" , Yicong Yang , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] arm64, mm: avoid always making PTE dirty in pte_mkwrite() In-Reply-To: (Catalin Marinas's message of "Fri, 17 Oct 2025 19:06:16 +0100") References: <20251015023712.46598-1-ying.huang@linux.alibaba.com> Date: Mon, 20 Oct 2025 19:00:20 +0800 Message-ID: <87bjm1g7nf.fsf@DESKTOP-5N7EMDA> User-Agent: Gnus/5.13 (Gnus v5.13) 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=ascii Hi, Catalin, Catalin Marinas writes: > On Wed, Oct 15, 2025 at 10:37:12AM +0800, Huang Ying wrote: >> Current pte_mkwrite_novma() makes PTE dirty unconditionally. This may >> mark some pages that are never written dirty wrongly. For example, >> do_swap_page() may map the exclusive pages with writable and clean PTEs >> if the VMA is writable and the page fault is for read access. >> However, current pte_mkwrite_novma() implementation always dirties the >> PTE. This may cause unnecessary disk writing if the pages are >> never written before being reclaimed. >> >> So, change pte_mkwrite_novma() to clear the PTE_RDONLY bit only if the >> PTE_DIRTY bit is set to make it possible to make the PTE writable and >> clean. >> >> The current behavior was introduced in commit 73e86cb03cf2 ("arm64: >> Move PTE_RDONLY bit handling out of set_pte_at()"). Before that, >> pte_mkwrite() only sets the PTE_WRITE bit, while set_pte_at() only >> clears the PTE_RDONLY bit if both the PTE_WRITE and the PTE_DIRTY bits >> are set. >> >> To test the performance impact of the patch, on an arm64 server >> machine, run 16 redis-server processes on socket 1 and 16 >> memtier_benchmark processes on socket 0 with mostly get >> transactions (that is, redis-server will mostly read memory only). >> The memory footprint of redis-server is larger than the available >> memory, so swap out/in will be triggered. Test results show that the >> patch can avoid most swapping out because the pages are mostly clean. >> And the benchmark throughput improves ~23.9% in the test. >> >> Fixes: 73e86cb03cf2 ("arm64: Move PTE_RDONLY bit handling out of set_pte_at()") >> Signed-off-by: Huang Ying >> Cc: Catalin Marinas >> Cc: Will Deacon >> Cc: Anshuman Khandual >> Cc: Ryan Roberts >> Cc: Gavin Shan >> Cc: Ard Biesheuvel >> Cc: "Matthew Wilcox (Oracle)" >> Cc: Yicong Yang >> Cc: linux-arm-kernel@lists.infradead.org >> Cc: linux-kernel@vger.kernel.org >> --- >> arch/arm64/include/asm/pgtable.h | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h >> index aa89c2e67ebc..0944e296dd4a 100644 >> --- a/arch/arm64/include/asm/pgtable.h >> +++ b/arch/arm64/include/asm/pgtable.h >> @@ -293,7 +293,8 @@ static inline pmd_t set_pmd_bit(pmd_t pmd, pgprot_t prot) >> static inline pte_t pte_mkwrite_novma(pte_t pte) >> { >> pte = set_pte_bit(pte, __pgprot(PTE_WRITE)); >> - pte = clear_pte_bit(pte, __pgprot(PTE_RDONLY)); >> + if (pte_sw_dirty(pte)) >> + pte = clear_pte_bit(pte, __pgprot(PTE_RDONLY)); >> return pte; >> } > > This seems to be the right thing. I recall years ago I grep'ed > (obviously not hard enough) and most pte_mkwrite() places had a > pte_mkdirty(). But I missed do_swap_page() and possibly others. The do_swap_page() change was introduced in June 2024, quite recently. > For this patch: > > Reviewed-by: Catalin Marinas Thanks! > I wonder whether we should also add (as a separate patch): > > diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c > index 830107b6dd08..df1c552ef11c 100644 > --- a/mm/debug_vm_pgtable.c > +++ b/mm/debug_vm_pgtable.c > @@ -101,6 +101,7 @@ static void __init pte_basic_tests(struct pgtable_debug_args *args, int idx) > WARN_ON(pte_dirty(pte_mkclean(pte_mkdirty(pte)))); > WARN_ON(pte_write(pte_wrprotect(pte_mkwrite(pte, args->vma)))); > WARN_ON(pte_dirty(pte_wrprotect(pte_mkclean(pte)))); > + WARN_ON(pte_dirty(pte_mkwrite_novma(pte_mkclean(pte)))); > WARN_ON(!pte_dirty(pte_wrprotect(pte_mkdirty(pte)))); > } > > For completeness, also (and maybe other combinations): > > WARN_ON(!pte_write(pte_mkdirty(pte_mkwrite_novma(pte)))); Sure. Will add another patch for this. > I cc'ed linux-mm in case we missed anything. If nothing raised, I'll > queue it next week. --- Best Regards, Huang, Ying