JOURNAL_TRY_TO_FREE_(9) The Linux Journalling API JOURNAL_TRY_TO_FREE_(9)NAMEjournal_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.
COPYRIGHTKernel Hackers Manual 2.6. November 2013 JOURNAL_TRY_TO_FREE_(9)
