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SubjectRe: OOM behavior in constrained memory situations
On Mon, Feb 06, 2006 at 04:03:53PM -0800, Christoph Lameter wrote:
> On Mon, 6 Feb 2006, Andrew Morton wrote:
>
> > The oom-killer is invoked from the page allocator. A hugetlb pagefault
> > won't use the page allocator. So there shouldn't be an oom-killing on
> > hugepage exhaustion.
>
> Right..... and the arch specific fault code (at least ia64) does not call
> the OOM killer.
>
> > I think this comment is just wrong:
> >
> > /* Logically this is OOM, not a SIGBUS, but an OOM
> > * could cause the kernel to go killing other
> > * processes which won't help the hugepage situation
> > * at all (?) */
> >
> > A VM_FAULT_OOM from there won't cause the oom-killer to do anything. We
> > should return VM_FAULT_OOM and let do_page_fault() commit suicide with
> > SIGKILL.
>
> Drop my patch that adds the comments explaining the bus error and add this
> fix instead. This will terminate an application with out of memory instead
> of bus error and remove the comment that you mentioned.

Looks good, except I think a comment should go in there so the next
person to look at it doesn't make the same wrong assumption I did,
that returning VM_FAULT_OOM will trigger the OOM killer.

> Signed-off-by: Christoph Lameter <clameter@sgi.com>
>
> Index: linux-2.6.16-rc2/mm/hugetlb.c
> ===================================================================
> --- linux-2.6.16-rc2.orig/mm/hugetlb.c 2006-02-02 22:03:08.000000000 -0800
> +++ linux-2.6.16-rc2/mm/hugetlb.c 2006-02-06 16:02:53.000000000 -0800
> @@ -391,12 +391,7 @@ static int hugetlb_cow(struct mm_struct
>
> if (!new_page) {
> page_cache_release(old_page);
> -
> - /* Logically this is OOM, not a SIGBUS, but an OOM
> - * could cause the kernel to go killing other
> - * processes which won't help the hugepage situation
> - * at all (?) */
> - return VM_FAULT_SIGBUS;
> + return VM_FAULT_OOM;
> }
>
> spin_unlock(&mm->page_table_lock);
> @@ -444,6 +439,7 @@ retry:
> page = alloc_huge_page(vma, address);
> if (!page) {
> hugetlb_put_quota(mapping);
> + ret = VM_FAULT_OOM;
> goto out;
> }
>
> -
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