From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with SMTP id 9751B8D000B for ; Sun, 24 Oct 2010 23:28:30 -0400 (EDT) Date: Mon, 25 Oct 2010 11:28:27 +0800 From: Wu Fengguang Subject: Re: [PATCH] do_migrate_range: avoid failure as much as possible Message-ID: <20101025032827.GA15933@localhost> References: <1287974851-4064-1-git-send-email-lliubbo@gmail.com> <20101025114017.86ee5e54.kamezawa.hiroyu@jp.fujitsu.com> <20101025025703.GA13858@localhost> <20101025120550.45745c3d.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20101025120550.45745c3d.kamezawa.hiroyu@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki Cc: Bob Liu , "akpm@linux-foundation.org" , "linux-mm@kvack.org" , "mel@csn.ul.ie" , "kosaki.motohiro@jp.fujitsu.com" List-ID: On Mon, Oct 25, 2010 at 11:05:50AM +0800, KAMEZAWA Hiroyuki wrote: > On Mon, 25 Oct 2010 10:57:03 +0800 > Wu Fengguang wrote: > > > On Mon, Oct 25, 2010 at 10:40:17AM +0800, KAMEZAWA Hiroyuki wrote: > > > On Mon, 25 Oct 2010 10:47:31 +0800 > > > Bob Liu wrote: > > > > > > > It's normal for isolate_lru_page() to fail at times. The failures are > > > > typically temporal and may well go away when offline_pages() retries > > > > the call. So it seems more reasonable to migrate as much as possible > > > > to increase the chance of complete success in next retry. > > > > > > > > This patch remove page_count() check and remove putback_lru_pages() and > > > > call migrate_pages() regardless of not_managed to reduce failure as much > > > > as possible. > > > > > > > > Signed-off-by: Bob Liu > > > > > > -EBUSY should be returned. > > > > It does return -EBUSY when ALL pages cannot be isolated from LRU (or > > is non-LRU pages at all). That means offline_pages() will repeat calls > > to do_migrate_range() as fast as possible as long as it can make > > progress. > > > I read the patch wrong ? "ret = -EBUSY" is dropped and "ret" will be > 0 or just a return code of migrate_page(). for () { ret = isolate_lru_page(page); } if (list_empty(&source)) goto out; out: return ret; So do_migrate_range() will return -EBUSY if the last isolate_lru_page() returns -EBUSY. > > > > > Is that behavior good enough? It does need some comment for this > > non-obvious return value. > > > > btw, the caller side code can be simplified (no behavior change). > > > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > > index dd186c1..606d358 100644 > > --- a/mm/memory_hotplug.c > > +++ b/mm/memory_hotplug.c > > @@ -848,17 +848,13 @@ repeat: > > pfn = scan_lru_pages(start_pfn, end_pfn); > > if (pfn) { /* We have page on LRU */ > > ret = do_migrate_range(pfn, end_pfn); > > - if (!ret) { > > - drain = 1; > > - goto repeat; > > - } else { > > - if (ret < 0) > > - if (--retry_max == 0) > > - goto failed_removal; > > + if (ret < 0) { > > + if (--retry_max <= 0) > > + goto failed_removal; > > yield(); > > - drain = 1; > > - goto repeat; > > } > > + drain = 1; > > + goto repeat; > > } > > This changes behavior. Ah yes! > This "ret" can be > 0 because migrate_page()'s return code is > "Return: Number of pages not migrated or error code." > > Then, > ret < 0 ===> maybe ebusy > ret > 0 ===> some pages are not migrated. maybe PG_writeback or some > ret == 0 ===> ok, all condition green. try next chunk soon. > > Then, I added "yield()" and --retrym_max for !ret cases. You are right, there is the "ret > 0, some pages are not migrated" case. But I'm not sure it's PG_writeback pages, because migrate_pages() will wait on writeback after pass 2. Thanks, Fengguang -- 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