From: Harshad Shirwadkar <harshadshirwadkar@xxxxxxxxx> This patch updates code documentation to reflect the commit path changes made in this series. Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@xxxxxxxxx> Reviewed-by: Jan Kara <jack@xxxxxxx> --- fs/ext4/fast_commit.c | 39 ++++++++++++++++++++++++++------------- 1 file changed, 26 insertions(+), 13 deletions(-) diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c index 266c95ff0d74..1691cfd89954 100644 --- a/fs/ext4/fast_commit.c +++ b/fs/ext4/fast_commit.c @@ -49,14 +49,21 @@ * that need to be committed during a fast commit in another in memory queue of * inodes. During the commit operation, we commit in the following order: * - * [1] Lock inodes for any further data updates by setting COMMITTING state - * [2] Submit data buffers of all the inodes - * [3] Wait for [2] to complete - * [4] Commit all the directory entry updates in the fast commit space - * [5] Commit all the changed inode structures - * [6] Write tail tag (this tag ensures the atomicity, please read the following + * [1] Lock the journal by calling jbd2_journal_lock_updates. This ensures that + * all the exsiting handles finish and no new handles can start. + * [2] Mark all the fast commit eligible inodes as undergoing fast commit + * by setting "EXT4_STATE_FC_COMMITTING" state. + * [3] Unlock the journal by calling jbd2_journal_unlock_updates. This allows + * starting of new handles. If new handles try to start an update on + * any of the inodes that are being committed, ext4_fc_track_inode() + * will block until those inodes have finished the fast commit. + * [4] Submit data buffers of all the committing inodes. + * [5] Wait for [4] to complete. + * [6] Commit all the directory entry updates in the fast commit space. + * [7] Commit all the changed inodes in the fast commit space and clear + * "EXT4_STATE_FC_COMMITTING" for these inodes. + * [8] Write tail tag (this tag ensures the atomicity, please read the following * section for more details). - * [7] Wait for [4], [5] and [6] to complete. * * All the inode updates must call ext4_fc_start_update() before starting an * update. If such an ongoing update is present, fast commit waits for it to @@ -142,6 +149,13 @@ * similarly. Thus, by converting a non-idempotent procedure into a series of * idempotent outcomes, fast commits ensured idempotence during the replay. * + * Locking + * ------- + * sbi->s_fc_lock protects the fast commit inodes queue and the fast commit + * dentry queue. ei->i_fc_lock protects the fast commit related info in a given + * inode. Most of the code avoids acquiring both the locks, but if one must do + * that then sbi->s_fc_lock must be acquired before ei->i_fc_lock. + * * TODOs * ----- * @@ -156,13 +170,12 @@ * fast commit recovery even if that area is invalidated by later full * commits. * - * 1) Fast commit's commit path locks the entire file system during fast - * commit. This has significant performance penalty. Instead of that, we - * should use ext4_fc_start/stop_update functions to start inode level - * updates from ext4_journal_start/stop. Once we do that we can drop file - * system locking during commit path. + * 1) Handle more ineligible cases. * - * 2) Handle more ineligible cases. + * 2) Change ext4_fc_commit() to lookup logical to physical mapping using extent + * status tree. This would get rid of the need to call ext4_fc_track_inode() + * before acquiring i_data_sem. To do that we would need to ensure that + * modified extents from the extent status tree are not evicted from memory. */ #include <trace/events/ext4.h> -- 2.36.0.rc0.470.gd361397f0d-goog
