On Fri, Aug 28, 2015 at 07:13:22PM +0200, Michal Hocko wrote:
...
> > * If the allocation doesn't have __GFP_WAIT, direct reclaim is
> > skipped. If a process performs only speculative allocations, it can
> > blow way past the high limit. This is actually easily reproducible
> > by simply doing "find /". VFS tries speculative !__GFP_WAIT
> > allocations first, so as long as there's memory which can be
> > consumed without blocking, it can keep allocating memory regardless
> > of the high limit.
>
> It is a bit confusing that you are talking about direct reclaim but in
> fact mean high limit reclaim. But yeah, you are right there is no
> protection against GFP_NOWAIT allocations there.
Actually, memory.high by itself *is* the protection against GFP_NOWAIT
allocations, similarly to zone watermarks. W/o it we would have no other
choice but fail a GFP_NOWAIT allocation on hitting memory.max. One
should just set it so that
memory.max - memory.high > [max sum size of !__GFP_WAIT allocations
that can normally occur in a row]
That being said, currently I don't see any point in making memory.high
!__GFP_WAIT-safe.
Thanks,
Vladimir
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