Re: [Devel] [PATCH hci-8.1 2/2] selftests/ve: check memory.numa_migrate keeps the folio order

[Pavel Tikhomirov <ptikhomirov@virtuozzo.com>]

> memcg_numa_migrate_new_folio() used to allocate a PMD-sized destination
> for every large folio. A page cache folio of a smaller order then ended
> up with a 512-page destination carrying its index and reference count.
> Only the source pages were copied into it, so a read of the folios that
> followed in the same 2 MB range was served from the uninitialised part
> of the destination, and the inode died in clear_inode() on eviction.
> 
> The test writes a file on an XFS image, where 64K writes produce large
> folios, from a cgroup bound to one NUMA node, migrates the cgroup to a
> second node, checks that something was migrated and reads the file back
> against the written pattern. On an unfixed kernel the comparison fails;
> the test then leaves the image mounted, because unlinking or unmounting
> would evict the inode and crash the node.
> 
> It needs root, two NUMA nodes with memory (numa=fake=2 is enough),
> cgroup2 with the memory and cpuset controllers, and mkfs.xfs, and skips
> otherwise.

This case looks a bit implicit, we rely on the size of huge pages XFS
allocates, maybe we can add folio size check, or somehow force
allocation of proper order. This is not blocking I guess.

-- 
Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
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