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Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.9.0 Subject: Re: [PATCH] mm: filemap: avoid unnecessary major faults in filemap_fault() Content-Language: en-US To: , CC: , , , , , , , , , References: <20231124023107.571059-1-zhangpeng362@huawei.com> From: "zhangpeng (AS)" In-Reply-To: <20231124023107.571059-1-zhangpeng362@huawei.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.179.160] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To kwepemm000020.china.huawei.com (7.193.23.93) X-CFilter-Loop: Reflected X-Rspam-User: X-Stat-Signature: 8f8ahmrqgjioegqotpnyheprwwzr63ax X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: D3DCA40009 X-HE-Tag: 1700797966-461606 X-HE-Meta: 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 s37hkCCv jqSA7kJGcbkV6WI5pZ19ypDSP0TgTg9YPYOjun4lPMk2NCBY2j4omQhQ0ybnos+Rx+ydphcXaaMxYEPrynk7M7dCebFpGVaUCyRn48RyefzXKe8BhzjwM3LJSRxaNn/EWgj06Do1ZOsIDnJkhUS8E15gRIqlqJ+cpwqbQEhDBDNWAijNnHQMEDpc8adxlw9zR0og1/30bLBuUIu2p0UQG+0O+fIrazjIkXGp2vzibbqnjNY4xqH23fUyL1XwIipmM2Ire82cVFPr5go6+OPKoaXx8s5CMxT9g2cLmENQrAtqHCRzN/tHkpgH9kw== 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: please ignore this... On 2023/11/24 10:31, Peng Zhang wrote: > 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 by holding ptl in filemap_fault() before > triggering a major fault. > > We tested the performance of file private mapping page fault > (page_fault2.c of will-it-scale [2]) and file shared mapping page fault > (page_fault3.c of will-it-scale). The difference in performance (in > operations per second) before and after patch applied is about 0.7% on a > x86 physical machine. > > [1] https://lore.kernel.org/linux-mm/9e62fd9a-bee0-52bf-50a7-498fa17434ee@huawei.com/ > [2] https://github.com/antonblanchard/will-it-scale/tree/master > > Suggested-by: "Huang, Ying" > Signed-off-by: ZhangPeng > Signed-off-by: Kefeng Wang > Reviewed-by: Yin Fengwei > --- > RFC->v1: - Update commit message and add RB from Yin Fengwei > - Add error handling when ptep == NULL per Huang, Ying and > Matthew Wilcox > > mm/filemap.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/mm/filemap.c b/mm/filemap.c > index 71f00539ac00..f3dcabdbc810 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -3226,6 +3226,20 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) > mapping_locked = true; > } > } else { > + pte_t *ptep = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd, > + vmf->address, &vmf->ptl); > + if (unlikely(!ptep)) > + return VM_FAULT_NOPAGE; > + /* > + * Recheck pte with ptl locked as the pte can be cleared > + * temporarily during a read/modify/write update. > + */ > + if (unlikely(!pte_none(ptep_get(ptep)))) > + ret = VM_FAULT_NOPAGE; > + pte_unmap_unlock(ptep, vmf->ptl); > + 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); -- Best Regards, Peng