From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nick Piggin Subject: Re: remove zero_page (was Re: -mm merge plans for 2.6.24) Date: Tue, 9 Oct 2007 19:31:51 +1000 References: <20071001142222.fcaa8d57.akpm@linux-foundation.org> <200710090117.47610.nickpiggin@yahoo.com.au> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200710091931.51564.nickpiggin@yahoo.com.au> Sender: owner-linux-mm@kvack.org Return-Path: To: Linus Torvalds Cc: Hugh Dickins , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: On Wednesday 10 October 2007 00:52, Linus Torvalds wrote: > On Tue, 9 Oct 2007, Nick Piggin wrote: > > I have done some tests which indicate a couple of very basic common tools > > don't do much zero-page activity (ie. kbuild). And also combined with > > some logical arguments to say that a "sane" app wouldn't be using > > zero_page much. (basically -- if the app cares about memory or cache > > footprint and is using many pages of zeroes, then it should have a more > > compressed representation of zeroes anyway). > > One of the things that zero-page has been used for is absolutely *huge* > (but sparse) arrays in Fortan programs. > > At least in traditional fortran, it was very hard to do dynamic > allocations, so people would allocate the *maximum* array statically, and > then not necessarily use everything. I don't know if the pages ever even > got paged in, In which case, they would not be using the ZERO_PAGE? If they were paging in (ie. reading) huge reams of zeroes, then maybe their algorithms aren't so good anyway? (I don't know). > but this is the kind of usage which is *not* insane. Yeah, that's why I use the double quotes... I wonder how to find out, though. I guess I could ask SGI if they could ask around -- but that still comes back to the problem of not being able to ever conclusively show that there are no real users of the ZERO_PAGE. Where do you suggest I go from here? Is there any way I can convince you to try it? Make it a config option? (just kidding) -- 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