Man page 9 : unmap_mapping_range

unmap_mapping_range - unmap the portion of all mmaps in the specified address_space corresponding to the specified page range in the underlying file.

void unmap_mapping_range(struct address_space *  mapping , loff_t const  holebegin , loff_t const  holelen , int  even_cows );

mapping
    the address space containing mmaps to be unmapped.

holebegin
    byte in first page to unmap, relative to the start of the underlying file. This will be rounded down to a PAGE_SIZE boundary. Note that this is different from truncate_pagecache, which must keep the partial page. In contrast, we must get rid of partial pages.

holelen
    size of prospective hole in bytes. This will be rounded up to a PAGE_SIZE boundary. A holelen of zero truncates to the end of the file.

even_cows
    1 when truncating a file, unmap even private COWed pages; but 0 when invalidating pagecache, donAqt throw away private data.