On Tue, Nov 4, 2014 at 3:53 PM, Minchan Kim <minchan@xxxxxxxxxx> wrote: > Hello, > > On Wed, Oct 29, 2014 at 03:43:33PM +0100, Vlastimil Babka wrote: >> On 10/16/2014 10:55 AM, Laura Abbott wrote: >> >On 10/15/2014 8:35 PM, Hui Zhu wrote: >> > >> >It's good to see another proposal to fix CMA utilization. Do you have >> >any data about the success rate of CMA contiguous allocation after >> >this patch series? I played around with a similar approach of using >> >CMA for MIGRATE_MOVABLE allocations and found that although utilization >> >did increase, contiguous allocations failed at a higher rate and were >> >much slower. I see what this series is trying to do with avoiding >> >allocation from CMA pages when a contiguous allocation is progress. >> >My concern is that there would still be problems with contiguous >> >allocation after all the MIGRATE_MOVABLE fallback has happened. >> >> Hi, >> >> did anyone try/suggest the following idea? >> >> - keep CMA as fallback to MOVABLE as is is now, i.e. non-agressive >> - when UNMOVABLE (RECLAIMABLE also?) allocation fails and CMA >> pageblocks have space, don't OOM immediately, but first try to >> migrate some MOVABLE pages to CMA pageblocks, to make space for the >> UNMOVABLE allocation in non-CMA pageblocks >> - this should keep CMA pageblocks free as long as possible and >> useful for CMA allocations, but without restricting the non-MOVABLE >> allocations even though there is free memory (but in CMA pageblocks) >> - the fact that a MOVABLE page could be successfully migrated to CMA >> pageblock, means it was not pinned or otherwise non-migratable, so >> there's a good chance it can be migrated back again if CMA >> pageblocks need to be used by CMA allocation > > I suggested exactly same idea long time ago. > >> - it's more complex, but I guess we have most of the necessary >> infrastructure in compaction already :) > > I agree but still, it doesn't solve reclaim problem(ie, VM doesn't > need to reclaim CMA pages when memory pressure of unmovable pages > happens). Of course, we could make VM be aware of that via introducing > new flag of __isolate_lru_page. > > However, I'd like to think CMA design from the beginning. > It made page allocation logic complicated, even very fragile as we > had recently and now we need to add new logics to migrate like you said. > As well, we need to fix reclaim path, too. > > It makes mm complicated day by day even though it doesn't do the role > enough well(ie, big latency and frequent allocation failure) so I really > want to stop making the mess bloated. > > Long time ago, when I saw Joonsoo's CMA agressive allocation patchset > (ie, roundrobin allocation between CMA and normal movable pages) > it was good to me at a first glance but it needs tweak of allocation > path and doesn't solve reclaim path, either. Yes, reclaim path could > be solved by another patch but I want to solve it altogether. > > At that time, I suggested big surgery to Joonsoo in offline that > let's move CMA allocation with movable zone allocation. With it, > we could make allocation/reclaim path simple but thing is we should > make VM be aware of overlapping MOVABLE zone which means some of pages > in the zone could be part of another zones but I think we already have > logics to handle it when I read comment in isolate_freepages so I think > the design should work. Thanks. > > A thing you guys might worry is bigger CMA latency because it makes > CMA memory usage ratio higher than the approach you mentioned but > anyone couldn't guarantee it once memory is fully utilized. > In addition, we have used fair zone allocator policy so it makes > round robin allocation automatically so I believe it should be way > to go. Even if kernel use it to allocate the CMA memory, CMA alloc latency will happen if most of memory is allocated and driver try to get CMA memory. https://lkml.org/lkml/2014/10/17/129 https://lkml.org/lkml/2014/10/17/130 These patches let cma_alloc do a shrink with function shrink_all_memory_for_cma if need. It handle a lot of latency issue in my part. And I think it can be more configurable for example some device use it and others not. Thanks, Hui > >> >> Thoughts? >> Vlastimil >> >> >Thanks, >> >Laura >> > >> >> -- >> 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> > > -- > Kind regards, > Minchan Kim > > -- > 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> -- 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>