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[37.188.180.223]) by smtp.gmail.com with ESMTPSA id t17sm1165030wrv.53.2020.04.01.23.44.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Apr 2020 23:44:38 -0700 (PDT) Date: Thu, 2 Apr 2020 08:44:37 +0200 From: Michal Hocko To: "Huang, Ying" Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Zi Yan , Andrea Arcangeli , "Kirill A . Shutemov" , Vlastimil Babka , Alexey Dobriyan , Konstantin Khlebnikov , =?iso-8859-1?B?Suly9G1l?= Glisse , Yang Shi Subject: Re: [PATCH -V2] /proc/PID/smaps: Add PMD migration entry parsing Message-ID: <20200402064437.GC22681@dhcp22.suse.cz> References: <20200402020031.1611223-1-ying.huang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200402020031.1611223-1-ying.huang@intel.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 02-04-20 10:00:31, Huang, Ying wrote: > From: Huang Ying > > Now, when read /proc/PID/smaps, the PMD migration entry in page table is simply > ignored. To improve the accuracy of /proc/PID/smaps, its parsing and processing > is added. > > Before the patch, for a fully populated 400 MB anonymous VMA, sometimes some THP > pages under migration may be lost as follows. Interesting. How did you reproduce this? [...] > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index 8d382d4ec067..9c72f9ce2dd8 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -546,10 +546,19 @@ static void smaps_pmd_entry(pmd_t *pmd, unsigned long addr, > struct mem_size_stats *mss = walk->private; > struct vm_area_struct *vma = walk->vma; > bool locked = !!(vma->vm_flags & VM_LOCKED); > - struct page *page; > + struct page *page = NULL; > > - /* FOLL_DUMP will return -EFAULT on huge zero page */ > - page = follow_trans_huge_pmd(vma, addr, pmd, FOLL_DUMP); > + if (pmd_present(*pmd)) { > + /* FOLL_DUMP will return -EFAULT on huge zero page */ > + page = follow_trans_huge_pmd(vma, addr, pmd, FOLL_DUMP); > + } else if (unlikely(thp_migration_supported() && is_swap_pmd(*pmd))) { > + swp_entry_t entry = pmd_to_swp_entry(*pmd); > + > + if (is_migration_entry(entry)) > + page = migration_entry_to_page(entry); > + else > + VM_WARN_ON_ONCE(1); Could you explain why do we need this WARN_ON? I haven't really checked the swap support for THP but cannot we have normal swap pmd entries? > + } > if (IS_ERR_OR_NULL(page)) > return; > if (PageAnon(page)) > @@ -578,8 +587,7 @@ static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, > > ptl = pmd_trans_huge_lock(pmd, vma); > if (ptl) { > - if (pmd_present(*pmd)) > - smaps_pmd_entry(pmd, addr, walk); > + smaps_pmd_entry(pmd, addr, walk); > spin_unlock(ptl); > goto out; > } > -- > 2.25.0 -- Michal Hocko SUSE Labs