From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx189.postini.com [74.125.245.189]) by kanga.kvack.org (Postfix) with SMTP id 35A926B0033 for ; Tue, 14 May 2013 17:09:07 -0400 (EDT) Message-ID: <5192A76E.6010509@redhat.com> Date: Tue, 14 May 2013 17:06:54 -0400 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [PATCH 7/9] mm: vmscan: Block kswapd if it is encountering pages under writeback References: <1368432760-21573-1-git-send-email-mgorman@suse.de> <1368432760-21573-8-git-send-email-mgorman@suse.de> In-Reply-To: <1368432760-21573-8-git-send-email-mgorman@suse.de> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Andrew Morton , Jiri Slaby , Valdis Kletnieks , Zlatko Calusic , Johannes Weiner , dormando , Michal Hocko , Kamezawa Hiroyuki , Linux-MM , LKML On 05/13/2013 04:12 AM, Mel Gorman wrote: > Historically, kswapd used to congestion_wait() at higher priorities if it > was not making forward progress. This made no sense as the failure to make > progress could be completely independent of IO. It was later replaced by > wait_iff_congested() and removed entirely by commit 258401a6 (mm: don't > wait on congested zones in balance_pgdat()) as it was duplicating logic > in shrink_inactive_list(). > > This is problematic. If kswapd encounters many pages under writeback and > it continues to scan until it reaches the high watermark then it will > quickly skip over the pages under writeback and reclaim clean young > pages or push applications out to swap. > > The use of wait_iff_congested() is not suited to kswapd as it will only > stall if the underlying BDI is really congested or a direct reclaimer was > unable to write to the underlying BDI. kswapd bypasses the BDI congestion > as it sets PF_SWAPWRITE but even if this was taken into account then it > would cause direct reclaimers to stall on writeback which is not desirable. > > This patch sets a ZONE_WRITEBACK flag if direct reclaim or kswapd is > encountering too many pages under writeback. If this flag is set and > kswapd encounters a PageReclaim page under writeback then it'll assume > that the LRU lists are being recycled too quickly before IO can complete > and block waiting for some IO to complete. > > Signed-off-by: Mel Gorman > Reviewed-by: Michal Hocko Acked-by: Rik van Riel -- 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