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X-IronPort-AV: E=McAfee;i="6600,9927,10974"; a="690672" X-IronPort-AV: E=Sophos;i="6.05,242,1701158400"; d="scan'208";a="690672" 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) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Rspamd-Queue-Id: D539320005 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: csjwkfbx7ugtfgbp615kpiyeqx1t7e7o X-HE-Tag: 1707101796-223642 X-HE-Meta: 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 9fmXoUUZ CtT3A8k0ReVu8iUrffypToNqZtyuNOvR2s/QYHa15I7mlPHKl04PjuZNyC+K3z/vgEnIdwK3ag0/+su2Nj77kWXqqqBVMyM/OrPt2TA9TB7Rz2dFqR/tkGUj/Fw1bTymamgeCc31idX6dy/PggoMURa52FNdH1FLxQKoWhjkijMB1ztS498SUTuwBM/AgnjjoaTE6cZIM0ToDWuqlL7RdJpkYyBtytIMmDmatBHr+BG2mZO1+S3NrQoVLwk+bPay1TmNPU9glxm9MYx/immzw3++FbBP6uvA0nsjFmkV+xduVL2dtcr9ge0lvQHmxq2MKRq5OfYLUuZZizeCNJQlJmetCll+PhFDm0oz1 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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);