From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with SMTP id D4DB96B02BA for ; Thu, 6 May 2010 11:45:34 -0400 (EDT) Message-ID: <4BE2E3F9.9090708@redhat.com> Date: Thu, 06 May 2010 11:44:57 -0400 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [PATCH 1/2] mm,migration: Prevent rmap_walk_[anon|ksm] seeing the wrong VMA information References: <1273159987-10167-1-git-send-email-mel@csn.ul.ie> <1273159987-10167-2-git-send-email-mel@csn.ul.ie> In-Reply-To: <1273159987-10167-2-git-send-email-mel@csn.ul.ie> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Mel Gorman Cc: Andrew Morton , Linux-MM , LKML , Minchan Kim , KAMEZAWA Hiroyuki , Christoph Lameter , Andrea Arcangeli , Linus Torvalds , Peter Zijlstra List-ID: On 05/06/2010 11:33 AM, Mel Gorman wrote: > @@ -1368,16 +1424,25 @@ static int rmap_walk_anon(struct page *page, int (*rmap_one)(struct page *, > * are holding mmap_sem. Users without mmap_sem are required to > * take a reference count to prevent the anon_vma disappearing > */ > - anon_vma = page_anon_vma(page); > + anon_vma = page_anon_vma_lock_root(page); > if (!anon_vma) > return ret; > - spin_lock(&anon_vma->lock); > list_for_each_entry(avc,&anon_vma->head, same_anon_vma) { One conceptual problem here. By taking the oldest anon_vma, instead of the anon_vma of the page, we may end up searching way too many processes. Eg. if the page is the page of a child process in a forking server workload, the above code will end up searching the parent and all of the siblings - even for a private page, in the child process's private anon_vma. For an Apache or Oracle system with 1000 clients (and child processes), that could be quite a drag - searching 1000 times as many processes as we should. -- 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