Messages in this thread | | | Date | Wed, 26 Aug 2009 21:44:44 +0200 | From | Andrea Arcangeli <> | Subject | Re: [PATCH 13/12] ksm: fix munlock during exit_mmap deadlock |
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On Wed, Aug 26, 2009 at 08:17:50PM +0100, Hugh Dickins wrote: > Has anyone looked at why Rawhide's mlockall is not faulting in the > pages, I wonder if there's a separate bug there?)
I reproduced only with self compiled mmotm kernel with full self compiled userland with just a mlockall and exit (not rawhide kernel/userland) so there's certainly no bug in rawhide, or at least nothing special about it.
> No, not while it's down inside page allocation.
There's a slight difference if it's ksm inside page allocation and not the task itself for other reasons. See the TIF_MEMDIE check in page_alloc.c, those won't trigger when it's ksm causing a page fault. So that's the problem left to tackle to make oom killer fully happy with KSK unshare.
> But you don't like that approach at all, hmm. It sounds like we'll > have a fight if I try either that or to reintroduce the ksm_test_exits
;) Well I'd rather have a more unfixable issue if we have to reintroduce the mm_users check the in page faults.
All is left to address is to teach page_alloc.c that the mm is going away in a second patch. That might also help when it's aio triggering gup page allocations or other kernel threads with use_mm just like ksm and the oom killer selected those "mm" for release.
Having ksm using use_mm before triggering the handle_mm_fault (so tsk->mm points to the mm of the task) and adding a MMF_MEMDIE to mm->flags checked by page_alloc would work just fine and should solve the double task killed... but then I'm unsure.. this is just the first idea I had.
> in memory.c, once the munlock faulting is eliminated. Well, I'll give > it more thought: your patch is a lot better than the status quo, > and should go in for now - thanks.
Ok, agreed!
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