From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f52.google.com (mail-pa0-f52.google.com [209.85.220.52]) by kanga.kvack.org (Postfix) with ESMTP id 04ECD6B0005 for ; Mon, 4 Apr 2016 01:54:14 -0400 (EDT) Received: by mail-pa0-f52.google.com with SMTP id zm5so136897733pac.0 for ; Sun, 03 Apr 2016 22:54:13 -0700 (PDT) Received: from mail-pf0-x233.google.com (mail-pf0-x233.google.com. [2607:f8b0:400e:c00::233]) by mx.google.com with ESMTPS id i71si21712648pfi.110.2016.04.03.22.54.13 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 03 Apr 2016 22:54:13 -0700 (PDT) Received: by mail-pf0-x233.google.com with SMTP id n1so31927799pfn.2 for ; Sun, 03 Apr 2016 22:54:13 -0700 (PDT) Subject: Re: [PATCH v3 01/16] mm: use put_page to free page instead of putback_lru_page References: <1459321935-3655-1-git-send-email-minchan@kernel.org> <1459321935-3655-2-git-send-email-minchan@kernel.org> From: Balbir Singh Message-ID: <57020177.60006@gmail.com> Date: Mon, 4 Apr 2016 15:53:59 +1000 MIME-Version: 1.0 In-Reply-To: <1459321935-3655-2-git-send-email-minchan@kernel.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Minchan Kim , Andrew Morton Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, jlayton@poochiereds.net, bfields@fieldses.org, Vlastimil Babka , Joonsoo Kim , koct9i@gmail.com, aquini@redhat.com, virtualization@lists.linux-foundation.org, Mel Gorman , Hugh Dickins , Sergey Senozhatsky , Rik van Riel , rknize@motorola.com, Gioh Kim , Sangseok Lee , Chan Gyun Jeong , Al Viro , YiPing Xu , Naoya Horiguchi On 30/03/16 18:12, 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. 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. So effectively when we return from unmap_and_move() the page is either put_page or putback_lru_page() and the page is gone from under us. -- 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