Re: [PATCH 13/12] ksm: fix munlock during exit_mmap deadlock

[Hugh Dickins]

On Wed, 26 Aug 2009, Andrea Arcangeli wrote:
> 
> 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.

Yes, I began to have thoughts along those lines too as I was writing
my reply.  It is a different angle on the problem, I hadn't looked at
it that way before, and it does seem worth pursuing.  MMF_MEMDIE, yes,
that might be useful.  But KSM_RUN_UNMERGE wouldn't be able to use_mm
since it's coming from a normal user process - perhaps it should be a
kill-me-first like swapoff via PF_SWAPOFF.

Hugh
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