Hello, 2016-01-23 1:38 GMT+09:00 Johannes Weiner <hannes@xxxxxxxxxxx>: > 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) As far as I know, there is no disagreement on this patchset in last year LSF/MM. Problem may be due to my laziness... Sorry about that. I will handle it soon. Is there anything more that you concern? > 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 I understand what Aneesh's problem is. Assume that X = non movable free page Y = movable free page Z = cma free page X < min watermark X + Y > high watermark Z > high watermark If there are bunch of consecutive movable allocation requests, Y will decrease. After some time, Y will be exhausted. At that time, there is enough Z so movable allocation request still can be handled in fastpath and kswapd isn't waked up. In that situation, if atomic non-movable page allocation for order-0 comes, it would be failed. Although it isn't mentioned on ZONE_CMA patchset, it is also fixed by that patchset because with that patchset, all CMA pages are in CMA zone so freepage calculation is always precise. Thanks. -- 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>