From mboxrd@z Thu Jan 1 00:00:00 1970 From: Con Kolivas Subject: Re: [PATCH] mm: yield during swap prefetching Date: Thu, 9 Mar 2006 13:30:13 +1100 References: <200603081013.44678.kernel@kolivas.org> <20060308222404.GA4693@elf.ucw.cz> <440F9154.2080909@yahoo.com.au> In-Reply-To: <440F9154.2080909@yahoo.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 8BIT Content-Disposition: inline Message-Id: <200603091330.14396.kernel@kolivas.org> Sender: owner-linux-mm@kvack.org Return-Path: To: Nick Piggin Cc: Pavel Machek , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, ck@vds.kolivas.org List-ID: On Thu, 9 Mar 2006 01:22 pm, Nick Piggin wrote: > Pavel Machek wrote: > >On Ut 07-03-06 16:05:15, Andrew Morton wrote: > >>Why do you want that? > >> > >>If prefetch is doing its job then it will save the machine from a pile of > >>major faults in the near future. The fact that the machine happens > > > >Or maybe not.... it is prefetch, it may prefetch wrongly, and you > >definitely want it doing nothing when system is loaded.... It only > >makes sense to prefetch when system is idle. > > Right. Prefetching is obviously going to have a very low work/benefit, > assuming your page reclaim is working properly, because a) it doesn't > deal with file pages, and b) it is doing work to reclaim pages that > have already been deemed to be the least important. > > What it is good for is working around our interesting VM that apparently > allows updatedb to swap everything out (although I haven't seen this > problem myself), and artificial memory hogs. By moving work to times of > low cost. No problem with the theory behind it. > > So as much as a major fault costs in terms of performance, the tiny > chance that prefetching will avoid it means even the CPU usage is > questionable. Using sched_yield() seems like a hack though. Yeah it's a hack alright. Funny how at last I find a place where yield does exactly what I want and because we hate yield so much noone wants me to use it all. Cheers, Con -- 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