On 10/15/2014 8:35 PM, Hui Zhu wrote:
In fallbacks of page_alloc.c, MIGRATE_CMA is the fallback of MIGRATE_MOVABLE. MIGRATE_MOVABLE will use MIGRATE_CMA when it doesn't have a page in order that Linux kernel want. If a system that has a lot of user space program is running, for instance, an Android board, most of memory is in MIGRATE_MOVABLE and allocated. Before function __rmqueue_fallback get memory from MIGRATE_CMA, the oom_killer will kill a task to release memory when kernel want get MIGRATE_UNMOVABLE memory because fallbacks of MIGRATE_UNMOVABLE are MIGRATE_RECLAIMABLE and MIGRATE_MOVABLE. This status is odd. The MIGRATE_CMA has a lot free memory but Linux kernel kill some tasks to release memory. This patch series adds a new function CMA_AGGRESSIVE to make CMA memory be more aggressive about allocation. If function CMA_AGGRESSIVE is available, when Linux kernel call function __rmqueue try to get pages from MIGRATE_MOVABLE and conditions allow, MIGRATE_CMA will be allocated as MIGRATE_MOVABLE first. If MIGRATE_CMA doesn't have enough pages for allocation, go back to allocate memory from MIGRATE_MOVABLE. Then the memory of MIGRATE_MOVABLE can be kept for MIGRATE_UNMOVABLE and MIGRATE_RECLAIMABLE which doesn't have fallback MIGRATE_CMA.
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. Thanks, Laura -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation -- 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>