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[37.188.180.223]) by smtp.gmail.com with ESMTPSA id u5sm13195631wrp.81.2020.04.03.06.11.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 03 Apr 2020 06:11:24 -0700 (PDT) Date: Fri, 3 Apr 2020 15:11:23 +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 -V3] /proc/PID/smaps: Add PMD migration entry parsing Message-ID: <20200403131123.GD22681@dhcp22.suse.cz> References: <20200403123059.1846960-1-ying.huang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200403123059.1846960-1-ying.huang@intel.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 03-04-20 20:30:59, 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. > > To test the patch, we run pmbench to eat 400 MB memory in background, then run > /usr/bin/migratepages and `cat /proc/PID/smaps` every second. The issue as > follows can be reproduced within 60 seconds. > > Before the patch, for the fully populated 400 MB anonymous VMA, some THP pages > under migration may be lost as below. > > 7f3f6a7e5000-7f3f837e5000 rw-p 00000000 00:00 0 > Size: 409600 kB > KernelPageSize: 4 kB > MMUPageSize: 4 kB > Rss: 407552 kB > Pss: 407552 kB > Shared_Clean: 0 kB > Shared_Dirty: 0 kB > Private_Clean: 0 kB > Private_Dirty: 407552 kB > Referenced: 301056 kB > Anonymous: 407552 kB > LazyFree: 0 kB > AnonHugePages: 405504 kB > ShmemPmdMapped: 0 kB > FilePmdMapped: 0 kB > Shared_Hugetlb: 0 kB > Private_Hugetlb: 0 kB > Swap: 0 kB > SwapPss: 0 kB > Locked: 0 kB > THPeligible: 1 > VmFlags: rd wr mr mw me ac > > After the patch, it will be always, > > 7f3f6a7e5000-7f3f837e5000 rw-p 00000000 00:00 0 > Size: 409600 kB > KernelPageSize: 4 kB > MMUPageSize: 4 kB > Rss: 409600 kB > Pss: 409600 kB > Shared_Clean: 0 kB > Shared_Dirty: 0 kB > Private_Clean: 0 kB > Private_Dirty: 409600 kB > Referenced: 294912 kB > Anonymous: 409600 kB > LazyFree: 0 kB > AnonHugePages: 407552 kB > ShmemPmdMapped: 0 kB > FilePmdMapped: 0 kB > Shared_Hugetlb: 0 kB > Private_Hugetlb: 0 kB > Swap: 0 kB > SwapPss: 0 kB > Locked: 0 kB > THPeligible: 1 > VmFlags: rd wr mr mw me ac > > Signed-off-by: "Huang, Ying" > Reviewed-by: Zi Yan > Cc: Andrea Arcangeli > Cc: Kirill A. Shutemov > Cc: Vlastimil Babka > Cc: Alexey Dobriyan > Cc: Michal Hocko > Cc: Konstantin Khlebnikov > Cc: "Jérôme Glisse" > Cc: Yang Shi Acked-by: Michal Hocko Thanks! > --- > > v3: > > - Revised patch description and remove VM_WARN_ON_ONCE() per Michal's comments > > v2: > > - Use thp_migration_supported() in condition to reduce code size if THP > migration isn't enabled. > > - Replace VM_BUG_ON() with VM_WARN_ON_ONCE(), it's not necessary to nuking > kernel for this. > > --- > fs/proc/task_mmu.c | 16 +++++++++++----- > 1 file changed, 11 insertions(+), 5 deletions(-) > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index 8d382d4ec067..36dc7417c0df 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -546,10 +546,17 @@ 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; > + > + 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); > > - /* FOLL_DUMP will return -EFAULT on huge zero page */ > - page = follow_trans_huge_pmd(vma, addr, pmd, FOLL_DUMP); > + if (is_migration_entry(entry)) > + page = migration_entry_to_page(entry); > + } > if (IS_ERR_OR_NULL(page)) > return; > if (PageAnon(page)) > @@ -578,8 +585,7 @@ 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