From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with ESMTP id 77359900086 for ; Mon, 18 Apr 2011 10:08:10 -0400 (EDT) Date: Mon, 18 Apr 2011 15:08:04 +0100 From: Mel Gorman Subject: Re: [PATCH 12/12] mm: Throttle direct reclaimers if PF_MEMALLOC reserves are low and swap is backed by network storage Message-ID: <20110418140804.GC16908@suse.de> References: <1302777698-28237-1-git-send-email-mgorman@suse.de> <1302777698-28237-13-git-send-email-mgorman@suse.de> <20110418223251.7ab148bb@notabene.brown> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20110418223251.7ab148bb@notabene.brown> Sender: owner-linux-mm@kvack.org List-ID: To: NeilBrown Cc: Linux-MM , Linux-Netdev , LKML , Peter Zijlstra On Mon, Apr 18, 2011 at 10:32:51PM +1000, NeilBrown wrote: > On Thu, 14 Apr 2011 11:41:38 +0100 Mel Gorman wrote: > > > If swap is backed by network storage such as NBD, there is a risk that a > > large number of reclaimers can hang the system by consuming all > > PF_MEMALLOC reserves. To avoid these hangs, the administrator must tune > > min_free_kbytes in advance. This patch will throttle direct reclaimers > > if half the PF_MEMALLOC reserves are in use as the system is at risk of > > hanging. A message will be displayed so the administrator knows that > > min_free_kbytes should be tuned to a higher value to avoid the > > throttling in the future. > > > > (I knew there was something else). > > I understand that there are suggestions that direct reclaim should always be > serialised as this reduces lock contention and improve data patterns (or > something like that). > AFAIK, this suggestion never got much beyond the "hand-waving" stage of development. It tended to trip up on the fact that such a feature could also throttle processes on machines with plenty of free clean unmapped pagecache which would be undesirable. > Would that make this patch redundant? Depends on how it was being serialised but .... > Or does this provide some extra > guarantee that the other proposal would not? > This patch could be extended to serialise direct reclaims in situations other than PFMEMALLOC is low if someone demonstrated the benefit. -- Mel Gorman 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org