From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 13 Feb 2003 15:40:40 -0700 From: Matt Porter To: vinai Cc: "LinuxPPC Developers' List" Subject: Re: vmalloc limits in PPC kernels ? Message-ID: <20030213154040.A1738@home.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: ; from vroopcha@mcw.edu on Thu, Feb 13, 2003 at 02:19:41PM -0600 Sender: owner-linuxppc-dev@lists.linuxppc.org List-Id: On Thu, Feb 13, 2003 at 02:19:41PM -0600, vinai wrote: > I've been doing a little work trying to update an in-house custom driver > for x86. We acquired fairly large chunks of data, and we can't afford > to lose any of it. To do this, we reserve a fairly large chunk of memory > in which the data can be stored, as we can't afford system latencies > when writing to disk. We were able to this in 2.2 without any problems, > but in 2.4, a new "feature" was introduced to x86 that limited how much > memory one can "vmalloc". I did a quick check, but didn't find anything > in the ppc asm directory. Do we have such a limit ? All architectures have a limit. Its size is defined by VMALLOC_END-VMALLOC_START and further limited by the size of each preceding allocation (+ a PAGE_SIZE pad) before the allocation in question. Allocations also include ioremaps and on some architectures consistent memory allocations absorb vmalloc space. You can see the constraints in asm-ppc/pgtable.h. On PPC, it is possible to change the default parameters in order to expand the amount of vmalloc space available. This is accomplished via config options under the advanced kernel options menu. With PAGE_OFFSET at 0x40000000 and highmem, I've run a system with nearly 3GB of vmalloc space. Regards, -- Matt Porter porter@cox.net This is Linux Country. On a quiet night, you can hear Windows reboot. ** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/