Messages in this thread | | | Date | Tue, 26 Apr 2016 15:50:06 +0100 | From | Mel Gorman <> | Subject | Re: [PATCH 15/28] mm, page_alloc: Move might_sleep_if check to the allocator slowpath |
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On Tue, Apr 26, 2016 at 03:41:22PM +0200, Vlastimil Babka wrote: > On 04/15/2016 11:07 AM, Mel Gorman wrote: > >There is a debugging check for callers that specify __GFP_DIRECT_RECLAIM > >from a context that cannot sleep. Triggering this is almost certainly > >a bug but it's also overhead in the fast path. > > For CONFIG_DEBUG_ATOMIC_SLEEP, enabling is asking for the overhead. But for > CONFIG_PREEMPT_VOLUNTARY which turns it into _cond_resched(), I guess it's > not. >
Either way, it struck me as odd. It does depend on the config and it's marginal so if there is a problem then I can drop it.
> >Move the check to the slow > >path. It'll be harder to trigger as it'll only be checked when watermarks > >are depleted but it'll also only be checked in a path that can sleep. > > Hmm what about zone_reclaim_mode=1, should the check be also duplicated to > that part of get_page_from_freelist()? >
zone_reclaim has a !gfpflags_allow_blocking() check, does not call cond_resched() before that check so it does not fall into an accidental sleep path. I'm not seeing why the check is necessary there.
-- Mel Gorman SUSE Labs
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