On Wed, 23 Nov 2011, Christoph Hellwig wrote:

It also seems like all fallocate implementaions for far got away
without the unmap_mapping_range, so either people didn't test them
hard enough, or tmpfs doesn't need it either.  I fear the former
is true.

They're saved by the funny little one-by-one unmap_mapping_range()
fallback in truncate_inode_page().  It's inefficient (in those rare
cases when someone is punching a hole somewhere that's mapped) and
we ought to do better, but we don't have an actual bug there.

Hugh

int truncate_inode_page(struct address_space *mapping, struct page *page)
{
	if (page_mapped(page)) {
		unmap_mapping_range(mapping,
				   (loff_t)page->index << PAGE_CACHE_SHIFT,
				   PAGE_CACHE_SIZE, 0);
	}
	return truncate_complete_page(mapping, page);
}

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