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HPT allocation failures on POWER8 KVM hosts

From: Roman Bolshakov
Subject: HPT allocation failures on POWER8 KVM hosts
Date: Fri, 15 Nov 2019 18:28:26 +0300

Hi Aneesh,

We're running a lot of KVM virtual machines on POWER8 hosts and
sometimes new VMs can't be started because there are no contiguous
regions for HPT because of CMA region fragmentation.

The issue is covered in the LWN article: https://lwn.net/Articles/684611/
The article points that you raised the problem on LSFMM 2016. However I
couldn't find a follow up article on the issue.

Looking at the kernel commit log I've identified a few commits that
might reduce CMA fragmentaiton and overcome HPT allocation failure:
  - bd2e75633c801 ("dma-contiguous: use fallback alloc_pages for single pages")
  - 678e174c4c16a ("powerpc/mm/iommu: allow migration of cma allocated
    pages during mm_iommu_do_alloc")
  - 9a4e9f3b2d739 ("mm: update get_user_pages_longterm to migrate pages 
allocated from
    CMA region")
  - d7fefcc8de914 ("mm/cma: add PF flag to force non cma alloc")

Are there any other commits that address the issue? What is the first
kernel version that shouldn't have the HPT allocation problem due to CMA

Thank you,

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