| jbd2_journal_try_to_free_buffers(9) - phpMan
JBD2_JOURNAL_TRY_TO_(9) The Linux Journalling API JBD2_JOURNAL_TRY_TO_(9)
NAME
jbd2_journal_try_to_free_buffers - try to free page buffers.
SYNOPSIS
int jbd2_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_DIRECT_RECLAIM 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
__jbd2_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 jbd2_journal_dirty_data on this buffer. So we need to
lock against that. jbd2_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 AT computer-surgery.uk>
Author.
Stephen Tweedie <sct AT redhat.com>
Author.
COPYRIGHT
Kernel Hackers Manual 4.8. January 2017 JBD2_JOURNAL_TRY_TO_(9)
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