From Bugzilla Helper: User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.7.10) Gecko/20050719 Red Hat/1.0.6-1.4.1 Firefox/1.0.6 Description of problem: On a 64 bit system with large amount of ram the vmalloc one can allocate should not be limited to 64Mb. A patch for this bug is already submited for the kernel 2.6.11 can this patch be back ported to 2.6.9? Here is a quote and the patch from Andi Kleen on the LKML The vmap vmalloc rework in 2.5 had a unintended side effect. vmalloc uses kmalloc now to allocate an array with a list of pages. kmalloc has a 128K maximum. This limits the vmalloc maximum size to 64MB on a 64bit system with 4K pages. That limit causes problems with other subsystems, e.g. iptables relies on allocating large vmallocs for its rule sets. This is a bug IMHO - on 64bit platforms there shouldn't be such a low limit on the vmalloc size. And even on 32bit it's too small for custom kernels with enlarged vmalloc area. Another problem is that this makes vmalloc unreliable. After the system has been running for some time it is unlikely that kmalloc will be able to allocate >order 2 pages due to memory fragmentation. This patch takes the easy way out for fixing this by just allocating this array with vmalloc when it is larger than a page. While more complicated and intrusive solutions would be possible they didn't use vmalloc recursively they didn't seem it worth to handle this very infrequent case. Please note that the vmalloc recursion is strictly bounded because each nested allocation will generate a much smaller stack frame. Also the kernel stack can handle even a few recursion steps easily because vmalloc has only a small stack frame. Signed-off-by: Andi Kleen <ak@xxxxxxx> diff -u linux-2.6.11rc3/mm/vmalloc.c-o linux-2.6.11rc3/mm/vmalloc.c --- linux-2.6.11rc3/mm/vmalloc.c-o 2005-02-04 09:13:51.000000000 +0100 +++ linux-2.6.11rc3/mm/vmalloc.c 2005-02-08 10:59:58.000000000 +0100 @@ -378,7 +378,10 @@ __free_page(area->pages[i]); } - kfree(area->pages); + if (area->nr_pages > PAGE_SIZE/sizeof(struct page *)) + vfree(area->pages); + else + kfree(area->pages); } kfree(area); @@ -482,7 +485,12 @@ array_size = (nr_pages * sizeof(struct page *)); area->nr_pages = nr_pages; - area->pages = pages = kmalloc(array_size, (gfp_mask & ~__GFP_HIGHMEM)); + /* Please note that the recursion is strictly bounded. */ + if (array_size > PAGE_SIZE) + pages = __vmalloc(array_size, gfp_mask, PAGE_KERNEL); + else + pages = kmalloc(array_size, (gfp_mask & ~__GFP_HIGHMEM)); + area->pages = pages; if (!area->pages) { remove_vm_area(area->addr); kfree(area); - Version-Release number of selected component (if applicable): kernel-2.6.9-22.EL How reproducible: Always Steps to Reproduce: 1.try to allocate more than 64Mb of vmalloc 2. 3. Actual Results: the allocation fails Expected Results: allocation succeed Additional info:
I submitted the patch to fix this in RHEL4 but it was too late for U3 so it has been postponed to RHEL4-U4. Larry Woodman
just curious, did you hit this in practice, or its just a theoretical problem?
Yes, we hit this in practice, we have a driver for an optimized file system which can allocates up the 512 Mb of vmalloc for huge disk arrays.
committed in stream U4 build 34.4. A test kernel with this patch is available from http://people.redhat.com/~jbaron/rhel4/
An advisory has been issued which should help the problem described in this bug report. This report is therefore being closed with a resolution of ERRATA. For more information on the solution and/or where to find the updated files, please follow the link below. You may reopen this bug report if the solution does not work for you. http://rhn.redhat.com/errata/RHSA-2006-0575.html
*** Bug 179098 has been marked as a duplicate of this bug. ***