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    SubjectRe: [PATCH][BUGFIX] vmscan: limit VM_EXEC protection to file pages
    On Tue, 13 Oct 2009, Wu Fengguang wrote:

    > It is possible to have !Anon but SwapBacked pages, and some apps could
    > create huge number of such pages with MAP_SHARED|MAP_ANONYMOUS. These
    > pages go into the ANON lru list, and hence shall not be protected: we
    > only care mapped executable files. Failing to do so may trigger OOM.
    >
    > Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
    > Reviewed-by: Rik van Riel <riel@redhat.com>
    > Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>

    I'm not going to stand against this patch. But I would like to point
    out that it will "penalize" (well, no longer favour) executables being
    run from a tmpfs. Probably not a big deal.

    And I want to put on record that (like Andrea) I really loathe this
    (vm_flags & VM_EXEC) test: it's a heuristic unlike any other in page
    reclaim, and one that is open to any application writer to take unfair
    advantage of.

    I know that it's there to make some things work better, and that it
    has been successful (though now inevitably it's found to require a
    tweak - how long until its next tweak?). But I do hope that one
    day you will come up with something much more satisfactory here.

    Hugh

    > ---
    > mm/vmscan.c | 2 +-
    > 1 file changed, 1 insertion(+), 1 deletion(-)
    >
    > --- linux.orig/mm/vmscan.c 2009-10-13 09:49:05.000000000 +0800
    > +++ linux/mm/vmscan.c 2009-10-13 09:49:37.000000000 +0800
    > @@ -1356,7 +1356,7 @@ static void shrink_active_list(unsigned
    > * IO, plus JVM can create lots of anon VM_EXEC pages,
    > * so we ignore them here.
    > */
    > - if ((vm_flags & VM_EXEC) && !PageAnon(page)) {
    > + if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
    > list_add(&page->lru, &l_active);
    > continue;
    > }


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