From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f176.google.com (mail-wi0-f176.google.com [209.85.212.176]) by kanga.kvack.org (Postfix) with ESMTP id C64B46B0253 for ; Tue, 4 Aug 2015 09:52:59 -0400 (EDT) Received: by wibxm9 with SMTP id xm9so167493184wib.0 for ; Tue, 04 Aug 2015 06:52:59 -0700 (PDT) Received: from mail-wi0-f176.google.com (mail-wi0-f176.google.com. [209.85.212.176]) by mx.google.com with ESMTPS id ld9si2402052wjc.86.2015.08.04.06.52.58 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 04 Aug 2015 06:52:58 -0700 (PDT) Received: by wibud3 with SMTP id ud3so24924047wib.0 for ; Tue, 04 Aug 2015 06:52:58 -0700 (PDT) Date: Tue, 4 Aug 2015 15:52:56 +0200 From: Michal Hocko Subject: Re: [PATCH] mm: vmscan: never isolate more pages than necessary Message-ID: <20150804135255.GG28571@dhcp22.suse.cz> References: <1438614147-30419-1-git-send-email-vdavydov@parallels.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1438614147-30419-1-git-send-email-vdavydov@parallels.com> Sender: owner-linux-mm@kvack.org List-ID: To: Vladimir Davydov Cc: Andrew Morton , Johannes Weiner , Vlastimil Babka , Minchan Kim , Mel Gorman , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Mon 03-08-15 18:02:27, Vladimir Davydov wrote: > If transparent huge pages are enabled, we can isolate many more pages > than we actually need to scan, because we count both single and huge > pages equally in isolate_lru_pages(). > > Since commit 5bc7b8aca942d ("mm: thp: add split tail pages to shrink > page list in page reclaim"), we scan all the tail pages immediately > after a huge page split (see shrink_page_list()). As a result, we can > reclaim up to SWAP_CLUSTER_MAX * HPAGE_PMD_NR (512 MB) in one run! 512MB is really unexpected. But yeah, you are right. Mel has increased SWAP_CLUSTER_MAX to 256 recently (mm: increase SWAP_CLUSTER_MAX to batch TLB flushes) which I have missed. That has made the situation potentially much worse. I guess this is worth mentioning in the changelog because the original SWAP_CLUSTER_MAX (32) hasn't looked that scary. > This is easy to catch on memcg reclaim with zswap enabled. The latter > makes swapout instant so that if we happen to scan an unreferenced huge > page we will evict both its head and tail pages immediately, which is > likely to result in excessive reclaim. > > Signed-off-by: Vladimir Davydov Reviewed-by: Michal Hocko > --- > mm/vmscan.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 5221e19e98f4..94092fd3b96b 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -1387,7 +1387,8 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, > unsigned long nr_taken = 0; > unsigned long scan; > > - for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) { > + for (scan = 0; scan < nr_to_scan && nr_taken < nr_to_scan && > + !list_empty(src); scan++) { > struct page *page; > int nr_pages; > > -- > 2.1.4 > -- Michal Hocko SUSE Labs -- 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