From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with ESMTP id 56FB36B01F1 for ; Mon, 15 Mar 2010 16:10:08 -0400 (EDT) Date: Mon, 15 Mar 2010 13:09:35 -0700 From: Andrew Morton Subject: Re: [RFC PATCH 0/3] Avoid the use of congestion_wait under zone pressure Message-Id: <20100315130935.f8b0a2d7.akpm@linux-foundation.org> In-Reply-To: <4B9E296A.2010605@linux.vnet.ibm.com> References: <1268048904-19397-1-git-send-email-mel@csn.ul.ie> <20100311154124.e1e23900.akpm@linux-foundation.org> <4B99E19E.6070301@linux.vnet.ibm.com> <20100312020526.d424f2a8.akpm@linux-foundation.org> <20100312104712.GB18274@csn.ul.ie> <4B9A3049.7010602@linux.vnet.ibm.com> <20100312093755.b2393b33.akpm@linux-foundation.org> <4B9E296A.2010605@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Christian Ehrhardt Cc: Mel Gorman , linux-mm@kvack.org, Nick Piggin , Chris Mason , Jens Axboe , linux-kernel@vger.kernel.org, gregkh@novell.com List-ID: On Mon, 15 Mar 2010 13:34:50 +0100 Christian Ehrhardt wrote: > c) If direct reclaim did reasonable progress in try_to_free but did not > get a page, AND there is no write in flight at all then let it try again > to free up something. > This could be extended by some kind of max retry to avoid some weird > looping cases as well. > > d) Another way might be as easy as letting congestion_wait return > immediately if there are no outstanding writes - this would keep the > behavior for cases with write and avoid the "running always in full > timeout" issue without writes. They're pretty much equivalent and would work. But there are two things I still don't understand: 1: Why is direct reclaim calling congestion_wait() at all? If no writes are going on there's lots of clean pagecache around so reclaim should trivially succeed. What's preventing it from doing so? 2: This is, I think, new behaviour. A regression. What caused it? -- 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