From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx162.postini.com [74.125.245.162]) by kanga.kvack.org (Postfix) with SMTP id 165AC6B005A for ; Sat, 9 Jun 2012 10:49:26 -0400 (EDT) Date: Sat, 9 Jun 2012 16:49:18 +0200 From: Johannes Weiner Subject: Re: [PATCH -V8 05/16] hugetlb: avoid taking i_mmap_mutex in unmap_single_vma() for hugetlb Message-ID: <20120609144918.GI1761@cmpxchg.org> References: <1339232401-14392-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1339232401-14392-6-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <20120609094444.GG1761@cmpxchg.org> <87sje4ljsm.fsf@skywalker.in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87sje4ljsm.fsf@skywalker.in.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Aneesh Kumar K.V" Cc: linux-mm@kvack.org, kamezawa.hiroyu@jp.fujitsu.com, dhillf@gmail.com, rientjes@google.com, mhocko@suse.cz, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org On Sat, Jun 09, 2012 at 06:33:05PM +0530, Aneesh Kumar K.V wrote: > Johannes Weiner writes: > > > On Sat, Jun 09, 2012 at 02:29:50PM +0530, Aneesh Kumar K.V wrote: > >> From: "Aneesh Kumar K.V" > >> > >> i_mmap_mutex lock was added in unmap_single_vma by 502717f4e ("hugetlb: > >> fix linked list corruption in unmap_hugepage_range()") but we don't use > >> page->lru in unmap_hugepage_range any more. Also the lock was taken > >> higher up in the stack in some code path. That would result in deadlock. > >> > >> unmap_mapping_range (i_mmap_mutex) > >> -> unmap_mapping_range_tree > >> -> unmap_mapping_range_vma > >> -> zap_page_range_single > >> -> unmap_single_vma > >> -> unmap_hugepage_range (i_mmap_mutex) > >> > >> For shared pagetable support for huge pages, since pagetable pages are ref > >> counted we don't need any lock during huge_pmd_unshare. We do take > >> i_mmap_mutex in huge_pmd_share while walking the vma_prio_tree in mapping. > >> (39dde65c9940c97f ("shared page table for hugetlb page")). > >> > >> Signed-off-by: Aneesh Kumar K.V > > > > This patch (together with the previous one) seems like a bugfix that's > > not really related to the hugetlb controller, unless I miss something. > > > > Could you please submit the fix separately? > > Patches upto 6 can really got in a separate series. I was not sure > whether I should split them. I will post that as a separate series now Ok, thanks, that will make it easier to upstream the controller. > > Maybe also fold the two patches into one and make it a single bugfix > > change that gets rid of the lock by switching away from page->lru. > > I wanted to make sure the patch that drop i_mmap_mutex is a separate one > so that we understand and document the locking details separately Nothing prevents you from writing a proper changelog :-) But changing from page->lru to an on-stack array does not have any merit by itself, so it just seems like a needless dependency between two patches that fix one problem (pita for backports into stable/distro kernels). -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org