[EE84M3i]

For the file being entirely pre-allocated case I understand, but for the file hole case I'm not sure I understand why you'd get such high disk activity.

If the index block also got evicted from the page cache, then could reading into a file hole still trigger a fault? Or is the "holiness" of a page for a mapping stored in the page table?

[loeg]

I suspect page size/aligned file holes could be backed by a read-only zero page via PTE as an optimization, but they might not be (I'm not as familiar with Linux mmap/filesystems as with FreeBSD).

It is quite possible the filesystem caches, e.g., the file extent tree (including holiness) separately from the backing inode/on-disk sectors for the tree.