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@xxxxxxx> > > (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@xxxxxxxxxxxxx> 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@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>