From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx145.postini.com [74.125.245.145]) by kanga.kvack.org (Postfix) with SMTP id 735F36B006C for ; Tue, 27 Nov 2012 06:59:34 -0500 (EST) Date: Tue, 27 Nov 2012 09:59:10 -0200 From: Rafael Aquini Subject: Re: [PATCH v11 4/7] mm: introduce compaction and migration for ballooned pages Message-ID: <20121127115910.GA1812@t510.redhat.com> References: <08be4346b620ae9344691cc6c2ad0bc51f492e01.1352256088.git.aquini@redhat.com> <20121109121602.GQ3886@csn.ul.ie> <20121120153324.7119bd3b.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121120153324.7119bd3b.akpm@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Mel Gorman , linux-mm@kvack.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Rusty Russell , "Michael S. Tsirkin" , Rik van Riel , Andi Kleen , Konrad Rzeszutek Wilk , Minchan Kim , Peter Zijlstra , "Paul E. McKenney" On Tue, Nov 20, 2012 at 03:33:24PM -0800, Andrew Morton wrote: > On Fri, 9 Nov 2012 12:16:02 +0000 > Mel Gorman wrote: > > > On Wed, Nov 07, 2012 at 01:05:51AM -0200, Rafael Aquini wrote: > > > Memory fragmentation introduced by ballooning might reduce significantly > > > the number of 2MB contiguous memory blocks that can be used within a guest, > > > thus imposing performance penalties associated with the reduced number of > > > transparent huge pages that could be used by the guest workload. > > > > > > This patch introduces the helper functions as well as the necessary changes > > > to teach compaction and migration bits how to cope with pages which are > > > part of a guest memory balloon, in order to make them movable by memory > > > compaction procedures. > > > > > > > ... > > > > > --- a/mm/compaction.c > > > +++ b/mm/compaction.c > > > @@ -14,6 +14,7 @@ > > > #include > > > #include > > > #include > > > +#include > > > #include "internal.h" > > > > > > #if defined CONFIG_COMPACTION || defined CONFIG_CMA > > > @@ -565,9 +566,24 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc, > > > goto next_pageblock; > > > } > > > > > > - /* Check may be lockless but that's ok as we recheck later */ > > > - if (!PageLRU(page)) > > > + /* > > > + * Check may be lockless but that's ok as we recheck later. > > > + * It's possible to migrate LRU pages and balloon pages > > > + * Skip any other type of page > > > + */ > > > + if (!PageLRU(page)) { > > > + if (unlikely(balloon_page_movable(page))) { > > > > Because it's lockless, it really seems that the barrier stuck down there > > is unnecessary. At worst you get a temporarily incorrect answer that you > > recheck later under page lock in balloon_page_isolate. > Sorry for the late reply. > What happened with this? > This Mel's concern were addressed by the last submitted review (v12) > Also: what barrier? Mel was refering to these barriers, at balloon_compaction.h: ---8<--- +/* + * balloon_page_insert - insert a page into the balloon's page list and make + * the page->mapping assignment accordingly. + * @page : page to be assigned as a 'balloon page' + * @mapping : allocated special 'balloon_mapping' + * @head : balloon's device page list head + */ +static inline void balloon_page_insert(struct page *page, + struct address_space *mapping, + struct list_head *head) +{ + list_add(&page->lru, head); + /* + * Make sure the page is already inserted on balloon's page list + * before assigning its ->mapping. + */ + smp_wmb(); + page->mapping = mapping; +} + +/* + * balloon_page_delete - clear the page->mapping and delete the page from + * balloon's page list accordingly. + * @page : page to be released from balloon's page list + */ +static inline void balloon_page_delete(struct page *page) +{ + page->mapping = NULL; + /* + * Make sure page->mapping is cleared before we proceed with + * balloon's page list deletion. + */ + smp_wmb(); + list_del(&page->lru); +} + +/* + * __is_movable_balloon_page - helper to perform @page mapping->flags tests + */ +static inline bool __is_movable_balloon_page(struct page *page) +{ + /* + * we might attempt to read ->mapping concurrently to other + * threads trying to write to it. + */ + struct address_space *mapping = ACCESS_ONCE(page->mapping); + smp_read_barrier_depends(); + return mapping_balloon(mapping); +} ---8<--- The last review got rid of them to stick with Mel's ACK. Cheers! --Rafael -- 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