From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id 32A2D8D003B for ; Sun, 27 Mar 2011 22:03:43 -0400 (EDT) Subject: [PATCH]mmap: avoid unnecessary anon_vma lock From: Shaohua Li 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 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: linux-mm , lkml , Rik van Riel , Hugh Dickins 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, 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