Messages in this thread | | | Date | Tue, 13 Oct 2009 12:33:58 +0100 (BST) | From | Hugh Dickins <> | Subject | Re: [PATCH][BUGFIX] vmscan: limit VM_EXEC protection to file pages |
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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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