Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751939Ab1DRDFZ (ORCPT ); Sun, 17 Apr 2011 23:05:25 -0400 Received: from smtp-out.google.com ([74.125.121.67]:22974 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751418Ab1DRDFU (ORCPT ); Sun, 17 Apr 2011 23:05:20 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=google.com; s=beta; h=date:from:x-x-sender:to:cc:subject:in-reply-to:message-id :references:user-agent:mime-version:content-type; b=dV33P8ocsc7S5l2l6zvkhqvJxmKnAeyYGldVjZRFPosy5jrphOcix3CnwU8X7lBEBo PbHJ8BCXGtZ+laZoIRKg== Date: Sun, 17 Apr 2011 20:05:19 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@sister.anvils To: Shaohua Li cc: Andrew Morton , linux-mm , lkml , Rik van Riel Subject: Re: [PATCH]mmap: avoid unnecessary anon_vma lock In-Reply-To: <1301277532.3981.25.camel@sli10-conroe> Message-ID: References: <1301277532.3981.25.camel@sli10-conroe> User-Agent: Alpine 2.00 (LSU 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1796 Lines: 41 On Mon, 28 Mar 2011, Shaohua Li wrote: > 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. > > Signed-off-by: Shaohua Li I was sceptical at first, but yes, you're right: thanks. Acked-by: Hugh Dickins > > --- > mm/mmap.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > Index: linux/mm/mmap.c > =================================================================== > --- linux.orig/mm/mmap.c 2011-03-24 09:08:27.000000000 +0800 > +++ linux/mm/mmap.c 2011-03-24 09:14:03.000000000 +0800 > @@ -605,7 +605,7 @@ again: remove_next = 1 + (end > next-> > * lock may be shared between many sibling processes. Skipping > * the lock for brk adjustments makes a difference sometimes. > */ > - if (vma->anon_vma && (insert || importer || start != vma->vm_start)) { > + if (vma->anon_vma && (importer || start != vma->vm_start)) { > anon_vma = vma->anon_vma; > anon_vma_lock(anon_vma); > } -- 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/