From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [RFC 0/7] Postphone reclaim laundry to write at high water marks From: Peter Zijlstra In-Reply-To: <20070823120819.GO13915@v2.random> References: <20070820215040.937296148@sgi.com> <1187692586.6114.211.camel@twins> <1187730812.5463.12.camel@lappy> <1187734144.5463.35.camel@lappy> <20070823120819.GO13915@v2.random> Content-Type: text/plain Date: Thu, 23 Aug 2007 14:59:48 +0200 Message-Id: <1187873988.6114.388.camel@twins> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Andrea Arcangeli Cc: Christoph Lameter , linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: On Thu, 2007-08-23 at 14:08 +0200, Andrea Arcangeli wrote: > On Wed, Aug 22, 2007 at 12:09:03AM +0200, Peter Zijlstra wrote: > > Strictly speaking: > > > > if: > > > > page = alloc_page(gfp); > > > > fails but: > > > > obj = kmem_cache_alloc(s, gfp); > > > > succeeds then its a bug. > > Why? this is like saying that if alloc_pages(order=1) fails but > alloc_pages(order=0) succeeds then it's a bug. Obviously it's not a > bug. > > The only bug is if slab allocations <=4k fails despite > alloc_pages(order=0) would succeed. That would be currently true. However I need it to be stricter. I'm wanting to do networked swap. And in order to be able to receive writeout completions when in the PF_MEMALLOC region I need to introduce a new network state. This is because it needs to operate in a steady state with limited (bounded) memory use. Normal network either consumes memory, or fails to receive anything at all. So this new network state will allocate space for a packet, receive the packet from the NIC, inspect the packet, and toss the packet when its not found to be aimed at the VM (ie. does not contain a writeout completion). So the total memory consumption of this state is 0 - it always frees what it takes, but the memory use is non 0 but bounded - it does temporarily use memory, but will limit itself to never exceed a given maximum) Because the network stack runs on the slab allocator in generic (both kmem_cache and kmalloc) I need this extra guarantee so that a slab allocated from the reserves will not serve objects to some random non-critical application. If this is not restricted this network state can leak memory to outside of PF_MEMALLOC and will not be stable. So what I need is: kmem_cache_alloc(s, gfp) to fail when alloc_page(gfp) fails agreeing on the extra condition: when kmem_cache_size(s) <= PAGE_SIZE and the extra note that: I only really need it to fail for ALLOC_NO_WATERMARKS, the other levels like ALLOC_HIGH and ALLOC_HARDER are not critical. Which ends up with: if the current gfp-context does not allow ALLOC_NO_WATERMARKS allocations, and alloc_page() fails, so must kmem_cache_alloc(s,) if kmem_cache_size(s) <= PAGE_SIZE. (yes this leaves jumbo frames broken) -- 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