From: Daniel Borkmann

Sent: 26 January 2017 09:37

...

quoted

quoted

I assume that kvzalloc() is still the same from [1], right? If so, then
it would unfortunately (partially) reintroduce the issue that was fixed.
If you look above at flags, they're also passed to __vmalloc() to not
trigger OOM in these situations I've experienced.

Pushing __GFP_NORETRY to __vmalloc doesn't have the effect you might
think it would. It can still trigger the OOM killer becauset the flags
are no propagated all the way down to all allocations requests (e.g.
page tables). This is the same reason why GFP_NOFS is not supported in
vmalloc.

Ok, good to know, is that somewhere clearly documented (like for the
case with kmalloc())? If not, could we do that for non-mm folks, or
at least add a similar WARN_ON_ONCE() as you did for kvmalloc() to make
it obvious to users that a given flag combination is not supported all
the way down?

ISTM that requests for the relatively small memory blocks needed for page
tables aren't really likely to invoke the OOM killer when it isn't already
being invoked by other actions. So that isn't really a problem.

More of a problem is that requests that you really don't mind failing
can use the last 'reasonably available' memory.
This will cause the next allocate to fail when it would be better for
the earlier one to fail instead.

	David

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