On 02.11.20 15:44, Matthew Wilcox wrote:
On Mon, Nov 02, 2020 at 06:39:20AM -0800, Chris Goldsworthy wrote:The current approach to increasing CMA utilization introduced in commit 16867664936e ("mm,page_alloc,cma: conditionally prefer cma pageblocks for movable allocations") increases CMA utilization by redirecting MIGRATE_MOVABLE allocations to a CMA region, when greater than half of the free pages in a given zone are CMA pages. The issue in this approach is that allocations with type MIGRATE_MOVABLE can still succumb to pinning. To get around this, one approach is to re-direct allocations to the CMA areas, that are known not to be victims of pinning. To this end, this series brings in __GFP_CMA, which we mark with allocations that we know are safe to be redirected to a CMA area.This feels backwards to me. What you're essentially saying is "Some allocations marked with GFP_MOVABLE turn out not to be movable, so we're going to add another GFP_REALLY_MOVABLE flag" instead of tracking down which GFP_MOVABLE allocations aren't really movable.
Right, this just sounds wrong. We have the exact same issues with long-term pinnings on ZONE_MOVABLE. We have known issues with short-term pinnings and movable allocations (e.g., when a process dies) that should be tackled instead.
This is just trying to work around the original issue. Nacked-by: David Hildenbrand <david@xxxxxxxxxx> -- Thanks, David / dhildenb
