From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with ESMTP id 9CBAC8D0040 for ; Tue, 29 Mar 2011 23:25:10 -0400 (EDT) Date: Wed, 30 Mar 2011 05:25:04 +0200 From: Andi Kleen Subject: Re: [PATCH]mmap: avoid unnecessary anon_vma lock Message-ID: <20110330032504.GD21838@one.firstfloor.org> References: <1301277532.3981.25.camel@sli10-conroe> <20110329153517.3b87842f.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110329153517.3b87842f.akpm@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Andi Kleen , Shaohua Li , linux-mm , lkml , Rik van Riel , Hugh Dickins On Tue, Mar 29, 2011 at 03:35:17PM -0700, Andrew Morton wrote: > On Mon, 28 Mar 2011 09:57:39 -0700 > Andi Kleen wrote: > > > Shaohua Li writes: > > > > > If we only change vma->vm_end, we can avoid taking anon_vma lock even 'insert' > > > isn't NULL, which is the case of split_vma. > > > From my understanding, we need the lock before because rmap must get the > > > 'insert' VMA when we adjust old VMA's vm_end (the 'insert' VMA is linked to > > > anon_vma list in __insert_vm_struct before). > > > But now this isn't true any more. The 'insert' VMA is already linked to > > > anon_vma list in __split_vma(with anon_vma_clone()) instead of > > > __insert_vm_struct. There is no race rmap can't get required VMAs. > > > So the anon_vma lock is unnecessary, and this can reduce one locking in brk > > > case and improve scalability. > > > > Looks good to me. > > Looks way too tricky to me. > > Please review this code for maintainability. Have we documented what > we're doing as completely and as clearly as we are able? I agree the comments could be improved, but the code change looked good to me. I don't think it impacts maintainability by itself because we already do similar magic. -Andi -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org