centos man page for journal_try_to_free_buffers

JOURNAL_TRY_TO_FREE_(9) 				     The Linux Journalling API					   JOURNAL_TRY_TO_FREE_(9)

NAME
       journal_try_to_free_buffers - try to free page buffers.

SYNOPSIS
       int journal_try_to_free_buffers(journal_t * journal, struct page * page, gfp_t gfp_mask);

ARGUMENTS
       journal
	   journal for operation

       page
	   to try and free

       gfp_mask
	   we use the mask to detect how hard should we try to release buffers. If __GFP_WAIT and __GFP_FS is set, we wait for commit code to
	   release the buffers.

DESCRIPTION
       For all the buffers on this page, if they are fully written out ordered data, move them onto BUF_CLEAN so try_to_free_buffers can reap
       them.

       This function returns non-zero if we wish try_to_free_buffers to be called. We do this if the page is releasable by try_to_free_buffers. We
       also do it if the page has locked or dirty buffers and the caller wants us to perform sync or async writeout.

       This complicates JBD locking somewhat. We aren't protected by the BKL here. We wish to remove the buffer from its committing or running
       transaction's ->t_datalist via __journal_unfile_buffer.

       This may *change* the value of transaction_t->t_datalist, so anyone who looks at t_datalist needs to lock against this function.

       Even worse, someone may be doing a journal_dirty_data on this buffer. So we need to lock against that.  journal_dirty_data will come out of
       the lock with the buffer dirty, which makes it ineligible for release here.

       Who else is affected by this? hmm... Really the only contender is do_get_write_access - it could be looking at the buffer while
       journal_try_to_free_buffer is changing its state. But that cannot happen because we never reallocate freed data as metadata while the data
       is part of a transaction. Yes?

       Return 0 on failure, 1 on success

AUTHORS
       Roger Gammans <rgammans@computer-surgery.co.uk>
	   Author.

       Stephen Tweedie <sct@redhat.com>
	   Author.

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014						   JOURNAL_TRY_TO_FREE_(9)