Messages in this thread | | | Date | Mon, 29 Jun 2009 16:35:26 -0700 (PDT) | From | David Rientjes <> | Subject | Re: upcoming kerneloops.org item: get_page_from_freelist |
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On Mon, 29 Jun 2009, Mel Gorman wrote:
> page-allocator: Ensure that processes that have been OOM killed exit the page allocator > > Processes that have been OOM killed set the thread flag TIF_MEMDIE. A > process such as this is expected to exit the page allocator but in the > event it happens to have set __GFP_NOFAIL, it potentially loops forever. >
That's not the expected behavior for TIF_MEMDIE, although your patch certainly changes that.
Your patch is simply doing
if (test_thread_flag(TIF_MEMDIE)) gfp_mask |= __GFP_NORETRY;
in the slowpath.
TIF_MEMDIE is supposed to allow allocations to succeed, not automatically fail, so that it can quickly handle its SIGKILL without getting blocked in the exit path seeking more memory.
> This patch checks TIF_MEMDIE when deciding whether to loop again in the > page allocator. Such a process will now return NULL after direct reclaim > and OOM killing have both been considered as options. The potential > problem is that a __GFP_NOFAIL allocation can still return failure so > callers must still handle getting returned NULL. >
All __GFP_NOFAIL allocations should ensure that alloc_pages() never returns NULL. Although it's unfortunate, that's the requirement that callers have been guaranteed and until they are fixed, the page allocator should respect it.
I disagree with this change because it unconditionally fails allocations when a task has been oom killed, a scenario which should be the _highest_ priority for allocations to succeed since it leads to future memory freeing.
Additionally, this will fail all GFP_ATOMIC allocations for oom killed tasks if allocating without watermarks fails although pdflush may concurrently be doing writeback or other allocation attempts are invoking direct reclaim.
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