From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f41.google.com (mail-wm0-f41.google.com [74.125.82.41]) by kanga.kvack.org (Postfix) with ESMTP id 49B576B0005 for ; Mon, 14 Mar 2016 04:48:39 -0400 (EDT) Received: by mail-wm0-f41.google.com with SMTP id n186so96589818wmn.1 for ; Mon, 14 Mar 2016 01:48:39 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id y4si17287379wme.87.2016.03.14.01.48.37 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 14 Mar 2016 01:48:38 -0700 (PDT) From: Vlastimil Babka Subject: Re: [PATCH v1 01/19] mm: use put_page to free page instead of putback_lru_page References: <1457681423-26664-1-git-send-email-minchan@kernel.org> <1457681423-26664-2-git-send-email-minchan@kernel.org> Message-ID: <56E67AE1.60700@suse.cz> Date: Mon, 14 Mar 2016 09:48:33 +0100 MIME-Version: 1.0 In-Reply-To: <1457681423-26664-2-git-send-email-minchan@kernel.org> Content-Type: text/plain; charset=iso-8859-2; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Minchan Kim , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, jlayton@poochiereds.net, bfields@fieldses.org, Joonsoo Kim , koct9i@gmail.com, aquini@redhat.com, virtualization@lists.linux-foundation.org, Mel Gorman , Hugh Dickins , Sergey Senozhatsky , rknize@motorola.com, Rik van Riel , Gioh Kim , Naoya Horiguchi On 03/11/2016 08:30 AM, Minchan Kim wrote: > Procedure of page migration is as follows: > > First of all, it should isolate a page from LRU and try to > migrate the page. If it is successful, it releases the page > for freeing. Otherwise, it should put the page back to LRU > list. > > For LRU pages, we have used putback_lru_page for both freeing > and putback to LRU list. It's okay because put_page is aware of > LRU list so if it releases last refcount of the page, it removes > the page from LRU list. However, It makes unnecessary operations > (e.g., lru_cache_add, pagevec and flags operations. Yeah, and compaction (perhaps also other migration users) has to drain the lru pvec... Getting rid of this stuff is worth even by itself. > It would be > not significant but no worth to do) and harder to support new > non-lru page migration because put_page isn't aware of non-lru > page's data structure. > > To solve the problem, we can add new hook in put_page with > PageMovable flags check but it can increase overhead in > hot path and needs new locking scheme to stabilize the flag check > with put_page. > > So, this patch cleans it up to divide two semantic(ie, put and putback). > If migration is successful, use put_page instead of putback_lru_page and > use putback_lru_page only on failure. That makes code more readable > and doesn't add overhead in put_page. I had an idea of checking for count==1 in putback_lru_page() which would take the put_page() shortcut from there. But maybe it can't be done nicely without races. > Cc: Vlastimil Babka > Cc: Mel Gorman > Cc: Hugh Dickins > Cc: Naoya Horiguchi > Signed-off-by: Minchan Kim Acked-by: Vlastimil Babka Note in -next/after 4.6-rc1 this will need some rebasing though. -- 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/ . Don't email: email@kvack.org