Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753521Ab1C1CDt (ORCPT ); Sun, 27 Mar 2011 22:03:49 -0400 Received: from mga11.intel.com ([192.55.52.93]:31922 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753282Ab1C1CDp (ORCPT ); Sun, 27 Mar 2011 22:03:45 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.63,252,1299484800"; d="scan'208";a="902440334" Subject: [PATCH]mmap: avoid unnecessary anon_vma lock From: Shaohua Li To: Andrew Morton Cc: linux-mm , lkml , Rik van Riel , Hugh Dickins Content-Type: text/plain; charset="UTF-8" Date: Mon, 28 Mar 2011 09:58:52 +0800 Message-ID: <1301277532.3981.25.camel@sli10-conroe> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1598 Lines: 37 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 --- 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/