From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with SMTP id A06F56B004D for ; Sat, 31 Oct 2009 18:29:18 -0400 (EDT) Date: Sat, 31 Oct 2009 23:29:06 +0100 From: Pavel Machek Subject: Re: [PATCH 2/3] page allocator: Do not allow interrupts to use ALLOC_HARDER Message-ID: <20091031222905.GA32720@elf.ucw.cz> References: <1256650833-15516-1-git-send-email-mel@csn.ul.ie> <1256650833-15516-3-git-send-email-mel@csn.ul.ie> <20091027130924.fa903f5a.akpm@linux-foundation.org> <20091031184054.GB1475@ucw.cz> <20091031201158.GB29536@elf.ucw.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org To: David Rientjes Cc: Andrew Morton , Mel Gorman , stable@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Frans Pop , Jiri Kosina , Sven Geggus , Karol Lewandowski , Tobias Oetiker , KOSAKI Motohiro , Pekka Enberg , Rik van Riel , Christoph Lameter , Stephan von Krawczynski , kernel-testers@vger.kernel.org List-ID: On Sat 2009-10-31 14:19:50, David Rientjes wrote: > On Sat, 31 Oct 2009, Pavel Machek wrote: > > > > Um, no, it's a matter of the kernel implementation. We allow such tasks > > > to allocate deeper into reserves to avoid the page allocator from > > > incurring a significant penalty when direct reclaim is required. > > > Background reclaim has already commenced at this point in the > > > slowpath. > > > > But we can't guarantee that enough memory will be ready in the > > reserves. So if realtime task relies on it, it is broken, and will > > fail to meet its deadlines from time to time. > > This is truly a bizarre tangent to take, I don't quite understand the > point you're trying to make. Memory reserves exist to prevent blocking > when we need memory the most (oom killed task or direct reclaim) and to > allocate from when we can't (GFP_ATOMIC) or shouldn't (rt tasks) utilize > direct reclaim. The idea is to kick background reclaim first in the > slowpath so we're only below the low watermark for a short period and > allow the allocation to succeed. If direct reclaim actually can't free > any memory, the oom killer will free it for us. > > So the realtime[*] tasks aren't relying on it at all, the ALLOC_HARDER > exemption for them in the page allocator are a convenience to return > memory faster than otherwise when the fastpath fails. I don't see much > point in arguing against that. Well, you are trying to make rt heuristic more precise. I believe it would be better to simply remove it. -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- 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