Joonsoo Kim <js1304@xxxxxxxxx> writes: > 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. > That is the issue I am hitting and if we don't have any blocker against ZONE_CMA then we can drop this topic. -aneesh -- 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>