Re: [patch 00/12] mm: page_alloc: improve OOM mechanism and policy

Michal Hocko
2015-04-01T15:19:27Z

On Mon 30-03-15 11:32:40, Dave Chinner wrote:
> On Fri, Mar 27, 2015 at 11:05:09AM -0400, Johannes Weiner wrote:
[...]
> > GFP_NOFS sites are currently one of the sites that can deadlock inside
> > the allocator, even though many of them seem to have fallback code.
> > My reasoning here is that if you *have* an exit strategy for failing
> > allocations that is smarter than hanging, we should probably use that.
>
> We already do that for allocations where we can handle failure in
> GFP_NOFS conditions. It is, however, somewhat useless if we can't
> tell the allocator to try really hard if we've already had a failure
> and we are already in memory reclaim conditions (e.g. a shrinker
> trying to clean dirty objects so they can be reclaimed).
>
> From that perspective, I think that this patch set aims force us
> away from handling fallbacks ourselves because a) it makes GFP_NOFS
> more likely to fail, and b) provides no mechanism to "try harder"
> when we really need the allocation to succeed.

You can ask for this "try harder" by __GFP_HIGH flag. Would that help
in your fallback case?
--
Michal Hocko
SUSE Labs