Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756171Ab3HBTlN (ORCPT ); Fri, 2 Aug 2013 15:41:13 -0400 Received: from zene.cmpxchg.org ([85.214.230.12]:51623 "EHLO zene.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755585Ab3HBTlL (ORCPT ); Fri, 2 Aug 2013 15:41:11 -0400 Date: Fri, 2 Aug 2013 15:41:02 -0400 From: Johannes Weiner To: Joonsoo Kim Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Joonsoo Kim , Minchan Kim , Mel Gorman , Rik van Riel Subject: Re: [PATCH 2/4] mm, migrate: allocation new page lazyily in unmap_and_move() Message-ID: <20130802194102.GV715@cmpxchg.org> References: <1375409279-16919-1-git-send-email-iamjoonsoo.kim@lge.com> <1375409279-16919-2-git-send-email-iamjoonsoo.kim@lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1375409279-16919-2-git-send-email-iamjoonsoo.kim@lge.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1691 Lines: 45 On Fri, Aug 02, 2013 at 11:07:57AM +0900, Joonsoo Kim wrote: > We don't need a new page and then go out immediately if some condition > is met. Allocation has overhead in comparison with some condition check, > so allocating lazyily is preferable solution. > > Signed-off-by: Joonsoo Kim > > diff --git a/mm/migrate.c b/mm/migrate.c > index 6f0c244..86db87e 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -864,10 +864,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private, > { > int rc = 0; > int *result = NULL; > - struct page *newpage = get_new_page(page, private, &result); > - > - if (!newpage) > - return -ENOMEM; > + struct page *newpage = NULL; > > if (page_count(page) == 1) { > /* page was freed from under us. So we are done. */ > @@ -878,6 +875,10 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private, > if (unlikely(split_huge_page(page))) > goto out; > > + newpage = get_new_page(page, private, &result); > + if (!newpage) > + return -ENOMEM; get_new_page() sets up result to communicate error codes from the following checks. While the existing ones (page freed and thp split failed) don't change rc, somebody else might add a condition whose error code should be propagated back into *result but miss it. Please leave get_new_page() where it is. The win from this change is not big enough to risk these problems. Thanks! -- 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/