Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754396Ab1C3DZK (ORCPT ); Tue, 29 Mar 2011 23:25:10 -0400 Received: from one.firstfloor.org ([213.235.205.2]:50660 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754086Ab1C3DZI (ORCPT ); Tue, 29 Mar 2011 23:25:08 -0400 Date: Wed, 30 Mar 2011 05:25:04 +0200 From: Andi Kleen To: Andrew Morton Cc: Andi Kleen , Shaohua Li , linux-mm , lkml , Rik van Riel , Hugh Dickins 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> User-Agent: Mutt/1.4.2.2i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1495 Lines: 34 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 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/