On Mon, Mar 08, 2021 at 02:53:23PM -0800, Darrick J. Wong wrote: > On Fri, Mar 05, 2021 at 04:11:11PM +1100, Dave Chinner wrote: > > From: Dave Chinner <dchinner@xxxxxxxxxx> > > > > 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 with 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> > > --- > > fs/xfs/libxfs/xfs_types.h | 1 + > > fs/xfs/xfs_buf_item.c | 2 +- > > fs/xfs/xfs_dquot_item.c | 2 +- > > fs/xfs/xfs_file.c | 14 +++++++------- > > fs/xfs/xfs_inode.c | 10 +++++----- > > fs/xfs/xfs_inode_item.c | 4 ++-- > > fs/xfs/xfs_inode_item.h | 2 +- > > fs/xfs/xfs_log.c | 27 ++++++++++++++------------- > > fs/xfs/xfs_log.h | 4 +--- > > fs/xfs/xfs_log_cil.c | 22 +++++++++------------- > > fs/xfs/xfs_log_priv.h | 15 +++++++-------- > > fs/xfs/xfs_trans.c | 6 +++--- > > fs/xfs/xfs_trans.h | 4 ++-- > > 13 files changed, 54 insertions(+), 59 deletions(-) > > > > diff --git a/fs/xfs/libxfs/xfs_types.h b/fs/xfs/libxfs/xfs_types.h > > index 064bd6e8c922..0870ef6f933d 100644 > > --- a/fs/xfs/libxfs/xfs_types.h > > +++ b/fs/xfs/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 */ > > I'm unfamiliar with the internal format of CIL sequence numbers. Do > they have the same cycle:offset segmented structure as LSNs do? Or are > they a simple linear integer that increases as we checkpoint committed > items? Monotonic increasing integer, only ever used in memory and never written to disk. > > Looking through the current code, I see a couple of places where we > initialize them to 1, and I also see that when we create a new cil > context we set its sequence to one more than the context that it will > replace. > > I also see a bunch of comparisons of cil context sequence numbers that > use standard integer operators, but then I also see one instance of: > > if (XFS_LSN_CMP(lip->li_seq, ctx->sequence) != 0) > return false; > return true > > in xfs_log_item_in_current_chkpt. AFAICT this could be replaced with a > simple: > > return lip->li_seq == ctx->sequence; Yup, missed that, will fix. -Dave. -- Dave Chinner david@xxxxxxxxxxxxx
