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[178.122.246.129]) by smtp.gmail.com with ESMTPSA id s10-v6sm525330wrw.35.2018.09.12.03.24.59 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 12 Sep 2018 03:24:59 -0700 (PDT) Received: by kshutemo-mobl1.localdomain (Postfix, from userid 1000) id 3B426300DB6; Wed, 12 Sep 2018 13:24:58 +0300 (+03) Date: Wed, 12 Sep 2018 13:24:58 +0300 From: "Kirill A. Shutemov" To: "Aneesh Kumar K.V" Cc: "Kirill A. Shutemov" , Andrew Morton , Vegard Nossum , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Zi Yan , Naoya Horiguchi , Vlastimil Babka , Andrea Arcangeli Subject: Re: [PATCH] mm, thp: Fix mlocking THP page with migration enabled Message-ID: <20180912102457.deuqtyx2b67zfi7u@kshutemo-mobl1> References: <20180911103403.38086-1-kirill.shutemov@linux.intel.com> <6fcb5b5b-43fa-f1d0-ce78-37fb51b46a75@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6fcb5b5b-43fa-f1d0-ce78-37fb51b46a75@linux.ibm.com> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 12, 2018 at 03:28:24PM +0530, Aneesh Kumar K.V wrote: > On 9/11/18 4:04 PM, Kirill A. Shutemov wrote: > > A transparent huge page is represented by a single entry on an LRU list. > > Therefore, we can only make unevictable an entire compound page, not > > individual subpages. > > > > If a user tries to mlock() part of a huge page, we want the rest of the > > page to be reclaimable. > > > > We handle this by keeping PTE-mapped huge pages on normal LRU lists: the > > PMD on border of VM_LOCKED VMA will be split into PTE table. > > > > Introduction of THP migration breaks the rules around mlocking THP > > pages. If we had a single PMD mapping of the page in mlocked VMA, the > > page will get mlocked, regardless of PTE mappings of the page. > > > > For tmpfs/shmem it's easy to fix by checking PageDoubleMap() in > > remove_migration_pmd(). > > > > Anon THP pages can only be shared between processes via fork(). Mlocked > > page can only be shared if parent mlocked it before forking, otherwise > > CoW will be triggered on mlock(). > > > > For Anon-THP, we can fix the issue by munlocking the page on removing PTE > > migration entry for the page. PTEs for the page will always come after > > mlocked PMD: rmap walks VMAs from oldest to newest. > > > > Test-case: > > > > #include > > #include > > #include > > #include > > #include > > > > int main(void) > > { > > unsigned long nodemask = 4; > > void *addr; > > > > addr = mmap((void *)0x20000000UL, 2UL << 20, PROT_READ | PROT_WRITE, > > MAP_PRIVATE | MAP_ANONYMOUS | MAP_LOCKED, -1, 0); > > > > if (fork()) { > > wait(NULL); > > return 0; > > } > > > > mlock(addr, 4UL << 10); > > mbind(addr, 2UL << 20, MPOL_PREFERRED | MPOL_F_RELATIVE_NODES, > > &nodemask, 4, MPOL_MF_MOVE | MPOL_MF_MOVE_ALL); > > > > return 0; > > } > > > > Signed-off-by: Kirill A. Shutemov > > Reported-by: Vegard Nossum > > Fixes: 616b8371539a ("mm: thp: enable thp migration in generic path") > > Cc: [v4.14+] > > Cc: Zi Yan > > Cc: Naoya Horiguchi > > Cc: Vlastimil Babka > > Cc: Andrea Arcangeli > > --- > > mm/huge_memory.c | 2 +- > > mm/migrate.c | 3 +++ > > 2 files changed, 4 insertions(+), 1 deletion(-) > > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > index 533f9b00147d..00704060b7f7 100644 > > --- a/mm/huge_memory.c > > +++ b/mm/huge_memory.c > > @@ -2931,7 +2931,7 @@ void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new) > > else > > page_add_file_rmap(new, true); > > set_pmd_at(mm, mmun_start, pvmw->pmd, pmde); > > - if (vma->vm_flags & VM_LOCKED) > > + if ((vma->vm_flags & VM_LOCKED) && !PageDoubleMap(new)) > > mlock_vma_page(new); > > update_mmu_cache_pmd(vma, address, pvmw->pmd); > > } > > diff --git a/mm/migrate.c b/mm/migrate.c > > index d6a2e89b086a..01dad96b25b5 100644 > > --- a/mm/migrate.c > > +++ b/mm/migrate.c > > @@ -275,6 +275,9 @@ static bool remove_migration_pte(struct page *page, struct vm_area_struct *vma, > > if (vma->vm_flags & VM_LOCKED && !PageTransCompound(new)) > > mlock_vma_page(new); > > + if (PageTransCompound(new) && PageMlocked(page)) > > + clear_page_mlock(page); > > + > > Can you explain this more? I am confused by the usage of 'new' and 'page' > there. 'new' is the PTE subpage of 'page'. clear_page_mlock() wants to see head page. I guess we can rewrite it more clearly: + if (PageTransHuge(page) && PageMlocked(page)) + clear_page_mlock(page); + > I guess the idea is if we are removing the migration pte at level 4 > table, and if we found the backing page compound don't mark the page > Mlocked? We has to clear mlock, not only don't mark it as such. remove_migration_pmd() for other VMA may mark it as mlock and we want to revert it on the first PTE mapping of the page. -- Kirill A. Shutemov