On 05/06/2015 12:09 AM, Nishanth Aravamudan wrote:

On 03.04.2015 [10:45:56 -0700], Nishanth Aravamudan wrote:

quoted

quoted

What I find somewhat worrying though is that we could potentially
break the pfmemalloc_watermark_ok() test in situations where
zone_reclaimable_pages(zone) == 0 is a transient situation (and not
a permanently allocated hugepage). In that case, the throttling is
supposed to help system recover, and we might be breaking that
ability with this patch, no?

Well, if it's transient, we'll skip it this time through, and once there
are reclaimable pages, we should notice it again.

I'm not familiar enough with this logic, so I'll read through the code
again soon to see if your concern is valid, as best I can.

In reviewing the code, I think that transiently unreclaimable zones will
lead to some higher direct reclaim rates and possible contention, but
shouldn't cause any major harm. The likelihood of that situation, as
well, in a non-reserved memory setup like the one I described, seems
exceedingly low.

OK, I guess when a reasonably configured system has nothing to reclaim, 
it's already busted and throttling won't change much.

Consider the patch Acked-by: Vlastimil Babka [off-list ref]

Thanks,
Nish