void truncate_inode_pages (struct address_space * mapping, loff_t lstart);
Truncate the page cache at a set offset, removing the pages that are beyond that offset (and zeroing out partial pages).
Truncate takes two passes - the first pass is nonblocking. It will not block on page locks and it will not block on writeback. The second pass will wait. This is to prevent as much IO as possible in the affected region. The first pass will remove most pages, so the search cost of the second pass is low.
When looking at page->index outside the page lock we need to be careful to copy it into a local to avoid races (it could change at any time).
We pass down the cache-hot hint to the page freeing code. Even if the mapping is large, it is probably the case that the final pages are the most recently touched, and freeing happens in ascending file offset order.
Called under (and serialised by) inode->i_sem.