Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751641AbaKDGEh (ORCPT ); Tue, 4 Nov 2014 01:04:37 -0500 Received: from mail-pa0-f41.google.com ([209.85.220.41]:50663 "EHLO mail-pa0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750968AbaKDGEd (ORCPT ); Tue, 4 Nov 2014 01:04:33 -0500 Date: Mon, 3 Nov 2014 22:04:24 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Davidlohr Bueso cc: "Kirill A. Shutemov" , Michel Lespinasse , akpm@linux-foundation.org, hughd@google.com, riel@redhat.com, mgorman@suse.de, peterz@infradead.org, mingo@kernel.org, linux-kernel@vger.kernel.org, dbueso@suse.de, linux-mm@kvack.org Subject: Re: [PATCH 08/10] mm/mremap: share the i_mmap_rwsem In-Reply-To: <1414697657-1678-9-git-send-email-dave@stgolabs.net> Message-ID: References: <1414697657-1678-1-git-send-email-dave@stgolabs.net> <1414697657-1678-9-git-send-email-dave@stgolabs.net> User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I'm glad to see this series back, and nicely presented: thank you. Not worth respinning them, but consider 1,2,3,4,5,6,7 and 9 as Acked-by: Hugh Dickins On Thu, 30 Oct 2014, Davidlohr Bueso wrote: > As per the comment in move_ptes(), we only require taking the > anon vma and i_mmap locks to ensure that rmap will always observe > either the old or new ptes, in the case of need_rmap_lock=true. > No modifications to the tree itself, thus share the i_mmap_rwsem. > > Signed-off-by: Davidlohr Bueso > Acked-by: Kirill A. Shutemov But this one is Nacked by me. I don't understand how you and Kirill could read Michel's painstaking comment on need_rmap_locks, then go go ahead and remove the exclusion of rmap_walk(). I agree the code here does not modify the interval tree, but the comment explains how we're moving a pte from one place in the tree to another, and in some cases there's a danger that the rmap walk might miss the pte from both places (which doesn't matter much to most of its uses, but is critical in page migration). Or am I the one missing something? Hugh > --- > mm/mremap.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/mremap.c b/mm/mremap.c > index c929324..09bd644 100644 > --- a/mm/mremap.c > +++ b/mm/mremap.c > @@ -119,7 +119,7 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, > if (need_rmap_locks) { > if (vma->vm_file) { > mapping = vma->vm_file->f_mapping; > - i_mmap_lock_write(mapping); > + i_mmap_lock_read(mapping); > } > if (vma->anon_vma) { > anon_vma = vma->anon_vma; > @@ -156,7 +156,7 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, > if (anon_vma) > anon_vma_unlock_read(anon_vma); > if (mapping) > - i_mmap_unlock_write(mapping); > + i_mmap_unlock_read(mapping); > } > > #define LATENCY_LIMIT (64 * PAGE_SIZE) > -- > 1.8.4.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/