From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f41.google.com (mail-pa0-f41.google.com [209.85.220.41]) by kanga.kvack.org (Postfix) with ESMTP id 87C2C6B0037 for ; Mon, 3 Feb 2014 22:48:07 -0500 (EST) Received: by mail-pa0-f41.google.com with SMTP id fa1so7966658pad.28 for ; Mon, 03 Feb 2014 19:48:07 -0800 (PST) Received: from mail-pa0-x230.google.com (mail-pa0-x230.google.com [2607:f8b0:400e:c03::230]) by mx.google.com with ESMTPS id qv10si1398505pbb.232.2014.02.03.19.48.06 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Mon, 03 Feb 2014 19:48:06 -0800 (PST) Received: by mail-pa0-f48.google.com with SMTP id kx10so7888596pab.21 for ; Mon, 03 Feb 2014 19:48:06 -0800 (PST) Date: Mon, 3 Feb 2014 19:47:21 -0800 (PST) From: Hugh Dickins Subject: Re: [patch] mm, compaction: avoid isolating pinned pages fix In-Reply-To: Message-ID: References: <20140203095329.GH6732@suse.de> <20140204000237.GA17331@lge.com> <20140204015332.GA14779@lge.com> <20140204021533.GA14924@lge.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: David Rientjes Cc: Joonsoo Kim , Mel Gorman , Andrew Morton , Rik van Riel , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Mon, 3 Feb 2014, David Rientjes wrote: > On Tue, 4 Feb 2014, Joonsoo Kim wrote: > > > > > Okay. It can't fix your situation. Anyway, *normal* anon pages may be mapped > > > > and have positive page_count(), so your code such as > > > > '!page_mapping(page) && page_count(page)' makes compaction skip these *normal* > > > > anon pages and this is incorrect behaviour. > > > > > > > > > > So how does that work with migrate_page_move_mapping() which demands > > > page_count(page) == 1 and the get_page_unless_zero() in > > > __isolate_lru_page()? > > > > Before doing migrate_page_move_mapping(), try_to_unmap() is called so that all > > mapping is unmapped. Then, remained page_count() is 1 which is grabbed by > > __isolate_lru_page(). Am I missing something? > > > > Ah, good point. I wonder if we can get away with > page_count(page) - page_mapcount(page) > 1 to avoid the get_user_pages() > pin? Something like that. But please go back to migrate_page_move_mapping() to factor in what it's additionally considering. Whether you can share code with it, I don't know - it has to do some things under a lock you cannot take at the preliminary stage - you haven't isolated or locked the page yet. There is a separate issue, that a mapping may supply its own non-default mapping->a_ops->migratepage(): can we assume that the page_counting is the same whatever migratepage() is in use? I'm not sure. If you stick to special-casing PageAnon pages, you won't face that issue; but your proposed change would be a lot more satisfying if we can convince ourselves that it's good for !PageAnon too. May need a trawl through the different migratepage() methods that exist in tree. 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/ . Don't email: email@kvack.org