From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.16]) (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 58B24101CE for ; Mon, 5 Feb 2024 02:56:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.16 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707101798; cv=none; b=Jg3Ijui1ggfjYZiBmJaDGMDKQCBDgZxAWpc/e9dcUf0Z04euvufGHywLhUEHRnvL40Kr3oDF4armUcprxT4dzdulpvFiVbLBre6Ee0GEgUvnRqDVM7ZHR9+BzWGGQ9HXguXHR05VitQLA0Wck8uDsEm93AAlcKDFa77P57rHg/I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707101798; c=relaxed/simple; bh=SZWNQ8FoWi3M3figUlWgt62ZFK1sUamebkXL8IH7FkQ=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=rFxOjvBgQNQNIcpQYZfwdloLQhD+6/pkKic1qVTIGHNKY5VHCiVsITBNmbV5apeIhK8XkiIE1Zr9sP2cIlfQQAMl9ykk+QNtM3boflgXC2zbP5ktBh8XsVD1Nrce4sLiBM1F6PShQNHEGxE+eW5VfHVVbeRGRo18OGMBZLa6uGw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=YKJWEpf9; arc=none smtp.client-ip=192.198.163.16 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="YKJWEpf9" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1707101796; x=1738637796; h=from:to:cc:subject:in-reply-to:references:date: message-id:mime-version; bh=SZWNQ8FoWi3M3figUlWgt62ZFK1sUamebkXL8IH7FkQ=; b=YKJWEpf9gWLbOtfUJMVtlBVTfSSevcfEigUqttHdyl7YZ165n5huCDYC ynbO9aIntAu2WAwWoqO6AZAyoNkWCtwNGoZeZfeUrvfgq5hBnkpqMFyPN qmQymRJimqDx0sGJ86UF7oL/jBczH277jPy6vqGTv7Fcb6aPqQGY9HW4N cVK/J09bp8QXU2tjFMKo8vdy78DX5wQz4l2x+MGtxW4y+YBOIhWzqcI4x yuDtt6VQBAysFzG/sQcAnpCVgOXP5R/v+K6DkfQ3bLk6e9RutgVSh7uXJ vaXQ/qUKMdR2EAkQqlH+dVWH/r6p0wZ7l4oodaNdrgWHY6JJfqPaVHa2r Q==; X-IronPort-AV: E=McAfee;i="6600,9927,10974"; a="690670" X-IronPort-AV: E=Sophos;i="6.05,242,1701158400"; d="scan'208";a="690670" Received: from fmviesa003.fm.intel.com ([10.60.135.143]) by fmvoesa110.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Feb 2024 18:56:35 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.05,242,1701158400"; d="scan'208";a="5222594" Received: from yhuang6-desk2.sh.intel.com (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.238.208.55]) by fmviesa003-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Feb 2024 18:56:32 -0800 From: "Huang, Ying" To: Peng Zhang Cc: , , , , , , , , , Subject: Re: [PATCH] filemap: avoid unnecessary major faults in filemap_fault() In-Reply-To: <20240204093526.212636-1-zhangpeng362@huawei.com> (Peng Zhang's message of "Sun, 4 Feb 2024 17:35:26 +0800") References: <20240204093526.212636-1-zhangpeng362@huawei.com> Date: Mon, 05 Feb 2024 10:54:36 +0800 Message-ID: <874jen4o43.fsf@yhuang6-desk2.ccr.corp.intel.com> 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 Peng Zhang writes: > From: ZhangPeng > > The major fault occurred when using mlockall(MCL_CURRENT | MCL_FUTURE) > in application, which leading to an unexpected performance issue[1]. > > This caused by temporarily cleared PTE during a read/modify/write update > of the PTE, eg, do_numa_page()/change_pte_range(). > > For the data segment of the user-mode program, the global variable area > is a private mapping. After the pagecache is loaded, the private anonymous > page is generated after the COW is triggered. Mlockall can lock COW pages > (anonymous pages), but the original file pages cannot be locked and may > be reclaimed. If the global variable (private anon page) is accessed when > vmf->pte is zeroed in numa fault, a file page fault will be triggered. > > At this time, the original private file page may have been reclaimed. > If the page cache is not available at this time, a major fault will be > triggered and the file will be read, causing additional overhead. > > Fix this by rechecking the PTE without acquiring PTL in filemap_fault() > before triggering a major fault. > > Testing file anonymous page read and write page fault performance in ext4 > and ramdisk using will-it-scale[2] on a x86 physical machine. The data > is the average change compared with the mainline after the patch is > applied. The test results are within the range of fluctuation, and there > is no obvious difference. The test results are as follows: > processes processes_idle threads threads_idle > ext4 file write: -1.14% -0.08% -1.87% 0.13% > ext4 file read: 0.03% -0.65% -0.51% -0.08% > ramdisk file write: -1.21% -0.21% -1.12% 0.11% > ramdisk file read: 0.00% -0.68% -0.33% -0.02% IIUC, this is the regression test results. Right? Can you also show improvement test results to justify the change? -- Best Regards, Huang, Ying > [1] https://lore.kernel.org/linux-mm/9e62fd9a-bee0-52bf-50a7-498fa17434ee@huawei.com/ > [2] https://github.com/antonblanchard/will-it-scale/ > > Suggested-by: "Huang, Ying" > Suggested-by: Yin Fengwei > Signed-off-by: ZhangPeng > Signed-off-by: Kefeng Wang > --- > RFC->v1: > - Add error handling when ptep == NULL per Huang, Ying and Matthew Wilcox > - Check the PTE without acquiring PTL in filemap_fault(), suggested by > Huang, Ying and Yin Fengwei > - Add pmd_none() check before PTE map > - Update commit message and add performance test information > > mm/filemap.c | 18 ++++++++++++++++++ > 1 file changed, 18 insertions(+) > > diff --git a/mm/filemap.c b/mm/filemap.c > index 142864338ca4..b29cdeb6a03b 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -3238,6 +3238,24 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) > mapping_locked = true; > } > } else { > + if (!pmd_none(*vmf->pmd)) { > + pte_t *ptep; > + > + ptep = pte_offset_map_nolock(vmf->vma->vm_mm, vmf->pmd, > + vmf->address, &vmf->ptl); > + if (unlikely(!ptep)) > + return VM_FAULT_NOPAGE; > + /* > + * Recheck pte as the pte can be cleared temporarily > + * during a read/modify/write update. > + */ > + if (unlikely(!pte_none(ptep_get_lockless(ptep)))) > + ret = VM_FAULT_NOPAGE; > + pte_unmap(ptep); > + if (unlikely(ret)) > + return ret; > + } > + > /* No page in the page cache at all */ > count_vm_event(PGMAJFAULT); > count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT);