From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx186.postini.com [74.125.245.186]) by kanga.kvack.org (Postfix) with SMTP id ABE406B006E for ; Thu, 16 Aug 2012 19:08:41 -0400 (EDT) Message-ID: <502D7D6E.8090303@linux.intel.com> Date: Thu, 16 Aug 2012 16:08:30 -0700 From: "H. Peter Anvin" MIME-Version: 1.0 Subject: Re: [PATCH, RFC 0/9] Introduce huge zero page References: <1344503300-9507-1-git-send-email-kirill.shutemov@linux.intel.com> <20120816122023.c0e9bbc0.akpm@linux-foundation.org> <20120816194024.GP11188@redhat.com> In-Reply-To: <20120816194024.GP11188@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrea Arcangeli Cc: Andrew Morton , "Kirill A. Shutemov" , linux-mm@kvack.org, Andi Kleen , linux-kernel@vger.kernel.org, "Kirill A. Shutemov" On 08/16/2012 12:40 PM, Andrea Arcangeli wrote: > Hi Andrew, > > On Thu, Aug 16, 2012 at 12:20:23PM -0700, Andrew Morton wrote: >> That's a pretty big improvement for a rather fake test case. I wonder >> how much benefit we'd see with real workloads? > > The same discussion happened about the zero page in general and > there's no easy answer. I seem to recall that it was dropped at some > point and then we reintroduced the zero page later. > > Most of the time it won't be worth it, it's just a few pathological > compute loads that benefits IIRC. So I'm overall positive about it > (after it's stable). > > Because this is done the right way (i.e. to allocate an hugepage at > the first wp fault, and to fallback exclusively if compaction fails) > it will help much less than the 4k zero pages if the zero pages are > scattered over the address space and not contiguous (it only helps if > there are 512 of them in a row). OTOH if they're contiguous, the huge > zero pages will perform better than the 4k zero pages. > One thing that I asked for testing a "virtual zero page" where the same page (or N pages for N-way page coloring) is reused across a page table. It would have worse TLB performance but likely *much* better cache behavior. -hpa -- 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