Provided by: linux-doc-2.6.15_2.6.15-23.39_all
journal_try_to_free_buffers - try to free page buffers.
int journal_try_to_free_buffers (journal_t * journal,
struct page * page,
journal for operation
page to try and free
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
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?
Roger Gammans <firstname.lastname@example.org>, Stephen Tweedie