From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 10 Nov 2005 15:13:29 -0800 (PST) From: Christoph Lameter Subject: Re: [RFC, PATCH] Slab counter troubles with swap prefetch? In-Reply-To: <200511111007.12872.kernel@kolivas.org> Message-ID: References: <200511111007.12872.kernel@kolivas.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Con Kolivas Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, alokk@calsoftinc.com List-ID: On Fri, 11 Nov 2005, Con Kolivas wrote: > > This patch splits the counter into the nr_local_slab which reflects > > slab pages allocated from the local zones (and this number is useful > > at least as a guidance for the VM) and the remotely allocated pages. > > How large a contribution is the remote slab size likely to be? Would this > information be useful to anyone potentially in future code besides swap > prefetch? The nature of prefetch is that this is only a fairly coarse measure > of how full the vm is with data we don't want to displace. Thus it is also > not important that it is very accurate. The size of the remote cache depends on many factors. The application can influence that by setting memory policies. > Unless the remote slab size can be a very large contribution, or having local Yes it can be quite large. On some of my tests with applications these are 100%. This is typical if the application sets the policy in such a way that all allocations are off node or if the kernel has to allocate memory on a certain node for a device. > and remote slab sizes is useful potentially to some other code I'm inclined > to say this is unnecessary. A simple comment saying something like "the > nr_slab estimation is artificially elevated by remote slab pages on numa, > however this contribution is not important to the accuracy of this > algorithm". Of course it is nice to be more accurate and if you think > worthwhile then we can do this - I'll be happy to be guided by your > judgement. > As a side note I doubt any serious size numa hardware will ever be idle enough > by swap prefetch standards to even start prefetching swap pages. If you think > hardware of this sort is likely to benefit from swap prefetch then perhaps we > should look at relaxing the conditions under which prefetching occurs. Small scale NUMA machines may benefit from swap prefetch but on larger machines people usually try to avoid swap altogether. -- 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