Re: [LSF/MM ATTEND] 2016: Requests to attend MM-summit

[Johannes Weiner <hannes@cmpxchg.org>]

Hi,

On Fri, Jan 22, 2016 at 10:11:12AM +0530, Aneesh Kumar K.V wrote:
> * CMA allocator issues:
>   (1) order zero allocation failures:
>       We are observing order zero non-movable allocation failures in kernel
> with CMA configured. We don't start a reclaim because our free memory check
> does not consider free_cma. Hence the reclaim code assume we have enough free
> pages. Joonsoo Kim tried to fix this with his ZOME_CMA patches. I would
> like to discuss the challenges in getting this merged upstream.
> https://lkml.org/lkml/2015/2/12/95 (ZONE_CMA)

The exclusion of cma pages from the watermark checks means that
reclaim is happening too early, not too late, which leaves memory
underutilized. That's what ZONE_CMA set out to fix.

But unmovable allocations can still fail when the only free memory is
inside CMA regions. I don't see how ZONE_CMA would fix that.

CC Joonsoo

But as Jan said, we discussed ZONE_CMA before, so it's not clear
whether rehashing it without new data points would be too useful.

> Others needed for the discussion:
> Joonsoo Kim <iamjoonsoo.kim@lge.com>
> 
>   (2) CMA allocation failures due to pinned pages in the region:
>       We allow only movable allocation from the CMA region to enable us
> to migrate those pages later when we get a CMA allocation request. But
> if we pin those movable pages, we will fail the migration which can result
> in CMA allocation failure. One such report can be found here.
> http://article.gmane.org/gmane.linux.kernel.mm/136738
> 
> Peter Zijlstra's VM_PINNED patch series should help in fixing the issue. I would
> like to discuss what needs to be done to get this patch series merged upstream
> https://lkml.org/lkml/2014/5/26/345 (VM_PINNED)
> 
> Others needed for the discussion:
> Peter Zijlstra <peterz@infradead.org>

There was no consensus whether this specific implementation would work
well for all sources of pinning. Giving this some time in the MM track
could be useful.

CC Peter

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>