Move the suitable huge orders validation into shmem_suitable_orders() for
tmpfs, which can reuse some code to simplify the logic.
In addition, we don't have special handling for the error code -E2BIG when
checking for conflicts with PMD sized THP in the pagecache for tmpfs, instead,
it will just fallback to order-0 allocations like this patch does, so this
simplification will not add functional changes.
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
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