From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Sat, 19 May 2007 03:22:35 +0200 From: Nick Piggin Subject: Re: [rfc] increase struct page size?! Message-ID: <20070519012235.GA15569@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: Hugh Dickins Cc: Linux Kernel Mailing List , Linux Memory Management List , linux-arch@vger.kernel.org List-ID: On Fri, May 18, 2007 at 04:42:10PM +0100, Hugh Dickins wrote: > On Fri, 18 May 2007, Nick Piggin wrote: > > > > If we add 8 bytes to struct page on 64-bit machines, it becomes 64 bytes, > > which is quite a nice number for cache purposes. > > > > 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. > > Sooner rather than later, don't we need those 8 bytes to expand from > atomic_t to atomic64_t _count and _mapcount? Not that we really need > all 64 bits of both, but I don't know how to work atomically with less. Yeah, that would be a very good use of it. > (Why do I have this sneaking feeling that you're actually wanting > to stick something into the lower bits of page->virtual?) No, I just thought I would get even more flamed if I was just adding padding that wasn't even doing _anything_ :) I remembered Ken had a benchmark where page_address was slow, and the rest is history... -- 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