From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757446AbcBWEKZ (ORCPT ); Mon, 22 Feb 2016 23:10:25 -0500 Received: from shelob.surriel.com ([74.92.59.67]:57139 "EHLO shelob.surriel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757310AbcBWEKF (ORCPT ); Mon, 22 Feb 2016 23:10:05 -0500 X-Greylist: delayed 1140 seconds by postgrey-1.27 at vger.kernel.org; Mon, 22 Feb 2016 23:10:05 EST Date: Mon, 22 Feb 2016 22:50:54 -0500 From: Rik van Riel To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, hannes@cmpxchg.org, akpm@linux-foundation.org, mgorman@suse.de Subject: [PATCH] mm,vmscan: compact memory from kswapd when lots of memory free already Message-ID: <20160222225054.1f6ab286@annuminas.surriel.com> X-Mailer: Claws Mail 3.12.0 (GTK+ 2.24.28; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If kswapd is woken up for a higher order allocation, for example from alloc_skb, but the system already has lots of memory free, kswapd_shrink_zone will rightfully decide kswapd should not free any more memory. However, at that point kswapd should proceed to compact memory, on behalf of alloc_skb or others. Currently kswapd will only compact memory if it first freed memory, leading kswapd to never compact memory when there is already lots of memory free. On my home system, that lead to kswapd occasionally using up to 5% CPU time, with many man wakeups from alloc_skb, and kswapd never doing anything to relieve the situation that caused it to be woken up. Going ahead with compaction when kswapd did not attempt to reclaim any memory, and as a consequence did not reclaim any memory, is the right thing to do in this situation. Signed-off-by: Rik van Riel --- mm/vmscan.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 71b1c29948db..9566a04b9759 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3343,7 +3343,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order, * Compact if necessary and kswapd is reclaiming at least the * high watermark number of pages as requsted */ - if (pgdat_needs_compaction && sc.nr_reclaimed > nr_attempted) + if (pgdat_needs_compaction && sc.nr_reclaimed >= nr_attempted) compact_pgdat(pgdat, order); /* -- -- All rights reversed.