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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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