Commit 76c39904 authored by Jan Kara's avatar Jan Kara Committed by Theodore Ts'o
Browse files

jbd2: cleanup needed free block estimates when starting a transaction 



__jbd2_log_space_left() and jbd_space_needed() were kind of odd.
jbd_space_needed() accounted also credits needed for currently
committing transaction while it didn't account for credits needed for
control blocks.  __jbd2_log_space_left() then accounted for control
blocks as a fraction of free space.  Since results of these two
functions are always only compared against each other, this works
correct but is somewhat strange.  Move the estimates so that
jbd_space_needed() returns number of blocks needed for a transaction
including control blocks and __jbd2_log_space_left() returns free
space in the journal (with the committing transaction already
subtracted).  Rename functions to jbd2_log_space_left() and
jbd2_space_needed() while we are changing them.

Reviewed-by: default avatarZheng Liu <wenqing.lz@taobao.com>
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent 2f387f84

fs/jbd2/checkpoint.c

+4 −4
Original line number Diff line number Diff line
@@ -120,8 +120,8 @@ void __jbd2_log_wait_for_space(journal_t *journal) 
	int nblocks, space_left;

	/* assert_spin_locked(&journal->j_state_lock); */



	nblocks = jbd_space_needed(journal);

	while (__jbd2_log_space_left(journal) < nblocks) {

	nblocks = jbd2_space_needed(journal);

	while (jbd2_log_space_left(journal) < nblocks) {

		if (journal->j_flags & JBD2_ABORT)

			return;

		write_unlock(&journal->j_state_lock);
@@ -140,8 +140,8 @@ void __jbd2_log_wait_for_space(journal_t *journal) 
		 */

		write_lock(&journal->j_state_lock);

		spin_lock(&journal->j_list_lock);

		nblocks = jbd_space_needed(journal);

		space_left = __jbd2_log_space_left(journal);

		nblocks = jbd2_space_needed(journal);

		space_left = jbd2_log_space_left(journal);

		if (space_left < nblocks) {

			int chkpt = journal->j_checkpoint_transactions != NULL;

			tid_t tid = 0;

fs/jbd2/journal.c

+0 −29
Original line number Diff line number Diff line
@@ -477,35 +477,6 @@ repeat: 
 * journal, so that we can begin checkpointing when appropriate.

 */



/*

 * __jbd2_log_space_left: Return the number of free blocks left in the journal.

 *

 * Called with the journal already locked.

 *

 * Called under j_state_lock

 */



int __jbd2_log_space_left(journal_t *journal)

{

	int left = journal->j_free;



	/* assert_spin_locked(&journal->j_state_lock); */



	/*

	 * Be pessimistic here about the number of those free blocks which

	 * might be required for log descriptor control blocks.

	 */



#define MIN_LOG_RESERVED_BLOCKS 32 /* Allow for rounding errors */



	left -= MIN_LOG_RESERVED_BLOCKS;



	if (left <= 0)

		return 0;

	left -= (left >> 3);

	return left;

}



/*

 * Called with j_state_lock locked for writing.

 * Returns true if a transaction commit was started.

fs/jbd2/transaction.c

+5 −4
Original line number Diff line number Diff line
@@ -283,12 +283,12 @@ repeat: 
	 * reduce the free space arbitrarily.  Be careful to account for

	 * those buffers when checkpointing.

	 */

	if (__jbd2_log_space_left(journal) < jbd_space_needed(journal)) {

	if (jbd2_log_space_left(journal) < jbd2_space_needed(journal)) {

		jbd_debug(2, "Handle %p waiting for checkpoint...\n", handle);

		atomic_sub(nblocks, &transaction->t_outstanding_credits);

		read_unlock(&journal->j_state_lock);

		write_lock(&journal->j_state_lock);

		if (__jbd2_log_space_left(journal) < jbd_space_needed(journal))

		if (jbd2_log_space_left(journal) < jbd2_space_needed(journal))

			__jbd2_log_wait_for_space(journal);

		write_unlock(&journal->j_state_lock);

		goto repeat;
@@ -306,7 +306,7 @@ repeat: 
	jbd_debug(4, "Handle %p given %d credits (total %d, free %d)\n",

		  handle, nblocks,

		  atomic_read(&transaction->t_outstanding_credits),

		  __jbd2_log_space_left(journal));

		  jbd2_log_space_left(journal));

	read_unlock(&journal->j_state_lock);



	lock_map_acquire(&handle->h_lockdep_map);
@@ -441,7 +441,8 @@ int jbd2_journal_extend(handle_t *handle, int nblocks) 
		goto unlock;

	}



	if (wanted > __jbd2_log_space_left(journal)) {

	if (wanted + (wanted >> JBD2_CONTROL_BLOCKS_SHIFT) >

	    jbd2_log_space_left(journal)) {

		jbd_debug(3, "denied handle %p %d blocks: "

			  "insufficient log space\n", handle, nblocks);

		goto unlock;

include/linux/jbd2.h

+26 −6
Original line number Diff line number Diff line
@@ -1220,7 +1220,6 @@ extern void jbd2_clear_buffer_revoked_flags(journal_t *journal); 
 * transitions on demand.

 */



int __jbd2_log_space_left(journal_t *); /* Called with journal locked */

int jbd2_log_start_commit(journal_t *journal, tid_t tid);

int __jbd2_log_start_commit(journal_t *journal, tid_t tid);

int jbd2_journal_start_commit(journal_t *journal, tid_t *tid);
@@ -1290,17 +1289,38 @@ static inline int tid_geq(tid_t x, tid_t y) 
extern int jbd2_journal_blocks_per_page(struct inode *inode);

extern size_t journal_tag_bytes(journal_t *journal);



/*

 * We reserve t_outstanding_credits >> JBD2_CONTROL_BLOCKS_SHIFT for

 * transaction control blocks.

 */

#define JBD2_CONTROL_BLOCKS_SHIFT 5



/*

 * Return the minimum number of blocks which must be free in the journal

 * before a new transaction may be started.  Must be called under j_state_lock.

 */

static inline int jbd_space_needed(journal_t *journal)

static inline int jbd2_space_needed(journal_t *journal)

{

	int nblocks = journal->j_max_transaction_buffers;

	if (journal->j_committing_transaction)

		nblocks += atomic_read(&journal->j_committing_transaction->

				       t_outstanding_credits);

	return nblocks;

	return nblocks + (nblocks >> JBD2_CONTROL_BLOCKS_SHIFT);

}



/*

 * Return number of free blocks in the log. Must be called under j_state_lock.

 */

static inline unsigned long jbd2_log_space_left(journal_t *journal)

{

	/* Allow for rounding errors */

	unsigned long free = journal->j_free - 32;



	if (journal->j_committing_transaction) {

		unsigned long committing = atomic_read(&journal->

			j_committing_transaction->t_outstanding_credits);



		/* Transaction + control blocks */

		free -= committing + (committing >> JBD2_CONTROL_BLOCKS_SHIFT);

	}

	return free;

}



/*

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