try_to_release_page — release old fs-specific metadata on a page
the page which the kernel is trying to free
memory allocation flags (and I/O mode)
The address_space is to try to release any data against the page (presumably at page->private). If the release was successful, return `1'. Otherwise return zero.
The gfp_mask argument specifies whether I/O may be performed to release this page (__GFP_IO), and whether the call may block (__GFP_WAIT & __GFP_FS).