From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with ESMTP id EE10A6B00A6 for ; Tue, 26 Jan 2010 11:42:45 -0500 (EST) Date: Tue, 26 Jan 2010 16:42:30 +0000 From: Mel Gorman Subject: Re: [PATCH 00 of 30] Transparent Hugepage support #3 Message-ID: <20100126164230.GC16468@csn.ul.ie> References: <20100122151947.GA3690@random.random> <20100123175847.GC6494@random.random> <4B5E3CC0.2060006@redhat.com> <20100126161625.GO30452@random.random> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20100126161625.GO30452@random.random> Sender: owner-linux-mm@kvack.org To: Andrea Arcangeli Cc: Christoph Lameter , Rik van Riel , linux-mm@kvack.org, Marcelo Tosatti , Adam Litke , Avi Kivity , Izik Eidus , Hugh Dickins , Nick Piggin , Andi Kleen , Dave Hansen , Benjamin Herrenschmidt , Ingo Molnar , Mike Travis , KAMEZAWA Hiroyuki , Chris Wright , Andrew Morton List-ID: On Tue, Jan 26, 2010 at 05:16:25PM +0100, Andrea Arcangeli wrote: > On Tue, Jan 26, 2010 at 09:54:59AM -0600, Christoph Lameter wrote: > > Huge pages are already in use through hugetlbs for such workloads. That > > works without swap. So why is this suddenly such a must have requirement? > > hugetlbfs is unusable when you're not doing a static alloc for 1 DBMS > in 1 machine with alloc size set in a config file that will then match > grub command line. > That may have been the case once upon a time but is far from accurate now. I routinely run benchmarks against a database using huge pages that isn't even hugepage-aware without going through insane steps. The huge pages are often allocated when the system has already been running several days (and in one case a few weeks) and I didn't have to be overly specific on how many huge pages I needed either as additional ones were allocated as required. hugetlbfs may be not be ideal, but it's not quite as catastrophic as commonly believed either. > > Why not swap 2M huge pages as a whole? > > That is nice thing to speedup swap bandwidth and reduce fragmentation, > just I couldn't make so many changes in one go. Later we can make this > change and remove a few split_huge_page from the rmap paths. > > > What in your workload forces hugetlb swap use? Just leaving a certain > > percentage of memory for 4k pages addresses the issue right now. > > hypervisor must be able to swap, furthermore when a VM exists we want > to be able to use that ram as pagecache (not to remain reserved in > some hugetlbfs). And we must be able to fallback to 4k allocations > always without userland being able to notice when unable to defrag, > all things hugetlbfs can't do. All designs that can't 100% fallback to > 4k allocations are useless in my view as far as you want to keep the > word "transparent" in the description of the patch... > -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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