From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Sat, 19 May 2007 03:25:30 +0200 From: Nick Piggin Subject: Re: [rfc] increase struct page size?! Message-ID: <20070519012530.GB15569@wotan.suse.de> References: <20070518040854.GA15654@wotan.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org Return-Path: To: Christoph Lameter Cc: Linux Kernel Mailing List , Linux Memory Management List , linux-arch@vger.kernel.org List-ID: On Fri, May 18, 2007 at 11:14:26AM -0700, Christoph Lameter wrote: > On Fri, 18 May 2007, Nick Piggin wrote: > > > However we don't have to let those 8 bytes go to waste: we can use them > > to store the virtual address of the page, which kind of makes sense for > > 64-bit, because they can likely to use complicated memory models. > > That is not a valid consideration anymore. There is virtual memmap update > pending with the sparsemem folks that will simplify things. > > > Many batch operations on struct page are completely random, and as such, I > > think it is better if each struct page fits completely into a single > > cacheline even if it means being slightly larger. > > Right. That would simplify the calculations. It isn't the calculations I'm worried about, although they'll get simpler too. It is the cache cost. > > Don't let this space go to waste though, we can use page->virtual in order > > to optimise page_address operations. > > page->virtual is a benefit if the page is cache hot. Otherwise it may > cause a useless lookup. It would be very rare for the page not to be in L1 cache at this point, because we've likely taken a reference on it and/or locked it or moved it between lists etc. > I wonder if there are other uses for the free space? Hugh points out that we should make _count and _mapcount atomic_long_t's, which would probably be a better use of the space once your vmemmap goes in. -- 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