From: Dave Chinner <dchinner@xxxxxxxxxx> Source kernel commit: 5f9b4b0de8dc2fb8eb655463b438001c111570fe In doing an investigation into AIL push stalls, I was looking at the log force code to see if an async CIL push could be done instead. This lead me to xfs_log_force_lsn() and looking at how it works. xfs_log_force_lsn() is only called from inode synchronisation contexts such as fsync(), and it takes the ip->i_itemp->ili_last_lsn value as the LSN to sync the log to. This gets passed to xlog_cil_force_lsn() via xfs_log_force_lsn() to flush the CIL to the journal, and then used by xfs_log_force_lsn() to flush the iclogs to the journal. The problem is that ip->i_itemp->ili_last_lsn does not store a log sequence number. What it stores is passed to it from the ->iop_committing method, which is called by xfs_log_commit_cil(). The value this passes to the iop_committing method is the CIL context sequence number that the item was committed to. As it turns out, xlog_cil_force_lsn() converts the sequence to an actual commit LSN for the related context and returns that to xfs_log_force_lsn(). xfs_log_force_lsn() overwrites it's "lsn" variable that contained a sequence with an actual LSN and then uses that to sync the iclogs. This caused me some confusion for a while, even though I originally wrote all this code a decade ago. ->iop_committing is only used by a couple of log item types, and only inode items use the sequence number it is passed. Let's clean up the API, CIL structures and inode log item to call it a sequence number, and make it clear that the high level code is using CIL sequence numbers and not on-disk LSNs for integrity synchronisation purposes. Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx> Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx> Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx> Reviewed-by: Allison Henderson <allison.henderson@xxxxxxxxxx> Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx> --- libxfs/xfs_types.h | 1 + 1 file changed, 1 insertion(+) diff --git a/libxfs/xfs_types.h b/libxfs/xfs_types.h index 064bd6e8..0870ef6f 100644 --- a/libxfs/xfs_types.h +++ b/libxfs/xfs_types.h @@ -21,6 +21,7 @@ typedef int32_t xfs_suminfo_t; /* type of bitmap summary info */ typedef uint32_t xfs_rtword_t; /* word type for bitmap manipulations */ typedef int64_t xfs_lsn_t; /* log sequence number */ +typedef int64_t xfs_csn_t; /* CIL sequence number */ typedef uint32_t xfs_dablk_t; /* dir/attr block number (in file) */ typedef uint32_t xfs_dahash_t; /* dir/attr hash value */
