From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx164.postini.com [74.125.245.164]) by kanga.kvack.org (Postfix) with SMTP id 48EB86B0146 for ; Sun, 19 Feb 2012 16:21:35 -0500 (EST) Received: by pbcwz17 with SMTP id wz17so6906861pbc.14 for ; Sun, 19 Feb 2012 13:21:34 -0800 (PST) Date: Sun, 19 Feb 2012 13:21:02 -0800 (PST) From: Hugh Dickins Subject: Re: [PATCH 2/6] thp: optimize away unnecessary page table locking In-Reply-To: <1328716302-16871-3-git-send-email-n-horiguchi@ah.jp.nec.com> Message-ID: References: <1328716302-16871-1-git-send-email-n-horiguchi@ah.jp.nec.com> <1328716302-16871-3-git-send-email-n-horiguchi@ah.jp.nec.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Naoya Horiguchi Cc: linux-mm@kvack.org, Andrew Morton , David Rientjes , Andi Kleen , Wu Fengguang , Andrea Arcangeli , KOSAKI Motohiro , KAMEZAWA Hiroyuki , linux-kernel@vger.kernel.org On Wed, 8 Feb 2012, Naoya Horiguchi wrote: > Currently when we check if we can handle thp as it is or we need to > split it into regular sized pages, we hold page table lock prior to > check whether a given pmd is mapping thp or not. Because of this, > when it's not "huge pmd" we suffer from unnecessary lock/unlock overhead. > To remove it, this patch introduces a optimized check function and > replace several similar logics with it. > > Signed-off-by: Naoya Horiguchi > Cc: David Rientjes > > Changes since v4: > - Rethink returned value of __pmd_trans_huge_lock() [snip] > --- 3.3-rc2.orig/mm/mremap.c > +++ 3.3-rc2/mm/mremap.c > @@ -155,8 +155,6 @@ unsigned long move_page_tables(struct vm_area_struct *vma, > if (err > 0) { > need_flush = true; > continue; > - } else if (!err) { > - split_huge_page_pmd(vma->vm_mm, old_pmd); > } > VM_BUG_ON(pmd_trans_huge(*old_pmd)); > } Is that what you intended to do there? I just hit that VM_BUG_ON on rc3-next-20120217. Hugh -- 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