From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [PATCH 0/5] make slab gfp fair From: Peter Zijlstra In-Reply-To: <20070514124451.c868c4c0.akpm@linux-foundation.org> References: <20070514131904.440041502@chello.nl> <20070514161224.GC11115@waste.org> <20070514124451.c868c4c0.akpm@linux-foundation.org> Content-Type: text/plain Date: Mon, 14 May 2007 22:05:29 +0200 Message-Id: <1179173129.2942.52.camel@lappy> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: Matt Mackall , Christoph Lameter , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Thomas Graf , David Miller , Daniel Phillips , Pekka Enberg List-ID: On Mon, 2007-05-14 at 12:44 -0700, Andrew Morton wrote: > On Mon, 14 May 2007 11:12:24 -0500 > Matt Mackall wrote: > > > If I understand this correctly: > > > > privileged thread unprivileged greedy process > > kmem_cache_alloc(...) > > adds new slab page from lowmem pool > > do_io() > > kmem_cache_alloc(...) > > kmem_cache_alloc(...) > > kmem_cache_alloc(...) > > kmem_cache_alloc(...) > > kmem_cache_alloc(...) > > ... > > eats it all > > kmem_cache_alloc(...) -> ENOMEM > > who ate my donuts?! > > Yes, that's my understanding also. > > I can see why it's a problem in theory, but I don't think Peter has yet > revealed to us why it's a problem in practice. I got all excited when > Christoph asked "I am not sure what the point of all of this is.", but > Peter cunningly avoided answering that ;) > > What observed problem is being fixed here? I'm moving towards swapping over networked storage. Admittedly a new feature. Like with pretty much all other swap solutions; there is the fundamental vm deadlock: freeing memory requires memory. Current block devices get around that by using mempools. This works well. However with network traffic mempools are not easily usable; the network stack uses kmalloc. By using reserve based allocation we can keep operating in a similar matter. -- 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