From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Lameter Date: Tue, 25 Mar 2008 17:48:19 +0000 Subject: Re: larger default page sizes... Message-Id: List-Id: References: <20080324.133722.38645342.davem@davemloft.net> <20080324.144356.104645106.davem@davemloft.net> In-Reply-To: <20080324.144356.104645106.davem@davemloft.net> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: David Miller Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-ia64@vger.kernel.org, torvalds@linux-foundation.org On Mon, 24 Mar 2008, David Miller wrote: > We should fix the underlying problems. > > I'm hitting issues on 128 cpu Niagara2 boxes, and it's all fundamental > stuff like contention on the per-zone page allocator locks. > > Which is very fixable, without going to larger pages. No its not fixable. You are doing linear optimizations to a slowdown that grows exponentially. Going just one order up for page size reduces the necessary locks and handling of the kernel by 50%. > > powerpc also runs HPC codes. They certainly see the same results > > that we see. > > There are ways to get large pages into the process address space for > compute bound tasks, without suffering the well known negative side > effects of using larger pages for everything. These hacks have limitations. F.e. they do not deal with I/O and require application changes.