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 471E26B01AD for ; Fri, 11 Jun 2010 02:17:31 -0400 (EDT) Date: Thu, 10 Jun 2010 23:17:06 -0700 From: Andrew Morton Subject: Re: [PATCH 6/6] vmscan: Do not writeback pages in direct reclaim Message-Id: <20100610231706.1d7528f2.akpm@linux-foundation.org> In-Reply-To: <1275987745-21708-7-git-send-email-mel@csn.ul.ie> References: <1275987745-21708-1-git-send-email-mel@csn.ul.ie> <1275987745-21708-7-git-send-email-mel@csn.ul.ie> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Mel Gorman Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Dave Chinner , Chris Mason , Nick Piggin , Rik van Riel List-ID: On Tue, 8 Jun 2010 10:02:25 +0100 Mel Gorman wrote: > When memory is under enough pressure, a process may enter direct > reclaim to free pages in the same manner kswapd does. If a dirty page is > encountered during the scan, this page is written to backing storage using > mapping->writepage. This can result in very deep call stacks, particularly > if the target storage or filesystem are complex. It has already been observed > on XFS that the stack overflows but the problem is not XFS-specific. > > This patch prevents direct reclaim writing back pages by not setting > may_writepage in scan_control. Instead, dirty pages are placed back on the > LRU lists for either background writing by the BDI threads or kswapd. If > in direct lumpy reclaim and dirty pages are encountered, the process will > kick the background flushter threads before trying again. > This wouldn't have worked at all well back in the days when you could dirty all memory with MAP_SHARED. The balance_dirty_pages() calls on the fault path will now save us but if for some reason we were ever to revert those, we'd need to revert this change too, I suspect. As it stands, it would be wildly incautious to make a change like this without first working out why we're pulling so many dirty pages off the LRU tail, and fixing that. -- 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