From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: Directories > 2GB Date: 16 Oct 2006 20:17:03 +0200 Message-ID: References: <20061004165655.GD22010@schatzie.adilger.int> <452AC4BE.6090905@xfs.org> <20061010015512.GQ11034@melbourne.sgi.com> <452B0240.60203@xfs.org> <20061010091904.GA395@infradead.org> <20061010233124.GX11034@melbourne.sgi.com> <452D2086.2020204__28695.6273987473$1160585745$gmane$org@xfs.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Christoph Hellwig , linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, xfs@oss.sgi.com Return-path: To: Steve Lord In-Reply-To: <452D2086.2020204__28695.6273987473$1160585745$gmane$org@xfs.org> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org Steve Lord writes: > David Chinner wrote: > > On Tue, Oct 10, 2006 at 10:19:04AM +0100, Christoph Hellwig wrote: > >> On Mon, Oct 09, 2006 at 09:15:28PM -0500, Steve Lord wrote: > >>> Hi Dave, > >>> > >>> My recollection is that it used to default to on, it was disabled > >>> because it needs to map the buffer into a single contiguous chunk > >>> of kernel memory. This was placing a lot of pressure on the memory > >>> remapping code, so we made it not default to on as reworking the > >>> code to deal with non contig memory was looking like a major > >>> effort. > >> Exactly. The code works but tends to go OOM pretty fast at least > >> when the dir blocksize code is bigger than the page size. I should > >> give the code a spin on my ppc box with 64k pages if it works better > >> there. > > The pagebuf code doesn't use high-order allocations anymore; it uses > > scatter lists and remapping to allow physically discontiguous pages > > in a multi-page buffer. That is, the pages are sourced via > > find_or_create_page() from the address space of the backing device, > > and then mapped via vmap() to provide a virtually contigous mapping > > of the multi-page buffer. > > So I don't think this problem exists anymore... > > I was not referring to high order allocations here, but the overhead > of doing address space remapping every time a directory is accessed. # grep -i vmalloc /proc/meminfo VmallocTotal: 34359738367 kB At least on 64bit systems it would be reasonable to keep a large number of directories mapped this way over a longer time. vmap() space is cheap there. -Andi