Messages in this thread | | | Subject | Re: [PATCH 0/2] Increasing CMA Utilization with a GFP Flag | From | David Hildenbrand <> | Date | Mon, 2 Nov 2020 18:35:08 +0100 |
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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@redhat.com>
-- Thanks,
David / dhildenb
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