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authorDave Chinner <dchinner@redhat.com>2022-07-07 11:56:09 +0300
committerDave Chinner <david@fromorbit.com>2022-07-07 11:56:09 +0300
commitd9f68777b2515452828d97b521ff8e3517b42eb1 (patch)
tree7aeb17c7a91128fec2ad867de43be473984f4482
parent1ccb0745a97fb8b38913b39b8ecb1aea39fdbcb0 (diff)
downloadlinux-d9f68777b2515452828d97b521ff8e3517b42eb1.tar.xz
xfs: xlog_sync() manually adjusts grant head space
When xlog_sync() rounds off the tail the iclog that is being flushed, it manually subtracts that space from the grant heads. This space is actually reserved by the transaction ticket that covers the xlog_sync() call from xlog_write(), but we don't plumb the ticket down far enough for it to account for the space consumed in the current log ticket. The grant heads are hot, so we really should be accounting this to the ticket is we can, rather than adding thousands of extra grant head updates every CIL commit. Interestingly, this actually indicates a potential log space overrun can occur when we force the log. By the time that xfs_log_force() pushes out an active iclog and consumes the roundoff space, the reservation for that roundoff space has been returned to the grant heads and is no longer covered by a reservation. In theory the roundoff added to log force on an already full log could push the write head past the tail. In practice, the CIL commit that writes to the log and needs the iclog pushed will have reserved space for roundoff, so when it releases the ticket there will still be physical space for the roundoff to be committed to the log, even though it is no longer reserved. This roundoff won't be enough space to allow a transaction to be woken if the log is full, so overruns should not actually occur in practice. That said, it indicates that we should not release the CIL context log ticket until after we've released the commit iclog. It also means that xlog_sync() still needs the direct grant head manipulation if we don't provide it with a ticket. Log forces are rare when we are in fast paths running 1.5 million transactions/s that make the grant heads hot, so let's optimise the hot case and pass CIL log tickets down to the xlog_sync() code. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Darrick J. Wong <djwong@kernel.org>
-rw-r--r--fs/xfs/xfs_log.c35
-rw-r--r--fs/xfs/xfs_log_cil.c20
-rw-r--r--fs/xfs/xfs_log_priv.h3
3 files changed, 41 insertions, 17 deletions
diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index 296f6ac43448..498cbb49392b 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -57,7 +57,8 @@ xlog_grant_push_ail(
STATIC void
xlog_sync(
struct xlog *log,
- struct xlog_in_core *iclog);
+ struct xlog_in_core *iclog,
+ struct xlog_ticket *ticket);
#if defined(DEBUG)
STATIC void
xlog_verify_grant_tail(
@@ -567,7 +568,8 @@ xlog_state_shutdown_callbacks(
int
xlog_state_release_iclog(
struct xlog *log,
- struct xlog_in_core *iclog)
+ struct xlog_in_core *iclog,
+ struct xlog_ticket *ticket)
{
xfs_lsn_t tail_lsn;
bool last_ref;
@@ -614,7 +616,7 @@ xlog_state_release_iclog(
trace_xlog_iclog_syncing(iclog, _RET_IP_);
spin_unlock(&log->l_icloglock);
- xlog_sync(log, iclog);
+ xlog_sync(log, iclog, ticket);
spin_lock(&log->l_icloglock);
return 0;
}
@@ -881,7 +883,7 @@ xlog_force_iclog(
iclog->ic_flags |= XLOG_ICL_NEED_FLUSH | XLOG_ICL_NEED_FUA;
if (iclog->ic_state == XLOG_STATE_ACTIVE)
xlog_state_switch_iclogs(iclog->ic_log, iclog, 0);
- return xlog_state_release_iclog(iclog->ic_log, iclog);
+ return xlog_state_release_iclog(iclog->ic_log, iclog, NULL);
}
/*
@@ -2027,7 +2029,8 @@ xlog_calc_iclog_size(
STATIC void
xlog_sync(
struct xlog *log,
- struct xlog_in_core *iclog)
+ struct xlog_in_core *iclog,
+ struct xlog_ticket *ticket)
{
unsigned int count; /* byte count of bwrite */
unsigned int roundoff; /* roundoff to BB or stripe */
@@ -2039,12 +2042,20 @@ xlog_sync(
count = xlog_calc_iclog_size(log, iclog, &roundoff);
- /* move grant heads by roundoff in sync */
- xlog_grant_add_space(log, &log->l_reserve_head.grant, roundoff);
- xlog_grant_add_space(log, &log->l_write_head.grant, roundoff);
+ /*
+ * If we have a ticket, account for the roundoff via the ticket
+ * reservation to avoid touching the hot grant heads needlessly.
+ * Otherwise, we have to move grant heads directly.
+ */
+ if (ticket) {
+ ticket->t_curr_res -= roundoff;
+ } else {
+ xlog_grant_add_space(log, &log->l_reserve_head.grant, roundoff);
+ xlog_grant_add_space(log, &log->l_write_head.grant, roundoff);
+ }
/* put cycle number in every block */
- xlog_pack_data(log, iclog, roundoff);
+ xlog_pack_data(log, iclog, roundoff);
/* real byte length */
size = iclog->ic_offset;
@@ -2277,7 +2288,7 @@ xlog_write_get_more_iclog_space(
spin_lock(&log->l_icloglock);
ASSERT(iclog->ic_state == XLOG_STATE_WANT_SYNC);
xlog_state_finish_copy(log, iclog, *record_cnt, *data_cnt);
- error = xlog_state_release_iclog(log, iclog);
+ error = xlog_state_release_iclog(log, iclog, ticket);
spin_unlock(&log->l_icloglock);
if (error)
return error;
@@ -2539,7 +2550,7 @@ xlog_write(
*/
spin_lock(&log->l_icloglock);
xlog_state_finish_copy(log, iclog, record_cnt, 0);
- error = xlog_state_release_iclog(log, iclog);
+ error = xlog_state_release_iclog(log, iclog, ticket);
spin_unlock(&log->l_icloglock);
return error;
@@ -2959,7 +2970,7 @@ restart:
* reference to the iclog.
*/
if (!atomic_add_unless(&iclog->ic_refcnt, -1, 1))
- error = xlog_state_release_iclog(log, iclog);
+ error = xlog_state_release_iclog(log, iclog, ticket);
spin_unlock(&log->l_icloglock);
if (error)
return error;
diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
index 78f8537860df..eccbfb99e894 100644
--- a/fs/xfs/xfs_log_cil.c
+++ b/fs/xfs/xfs_log_cil.c
@@ -1189,6 +1189,7 @@ xlog_cil_push_work(
xfs_csn_t push_seq;
bool push_commit_stable;
LIST_HEAD (whiteouts);
+ struct xlog_ticket *ticket;
new_ctx = xlog_cil_ctx_alloc();
new_ctx->ticket = xlog_cil_ticket_alloc(log);
@@ -1323,7 +1324,14 @@ xlog_cil_push_work(
if (error)
goto out_abort_free_ticket;
- xfs_log_ticket_ungrant(log, ctx->ticket);
+ /*
+ * Grab the ticket from the ctx so we can ungrant it after releasing the
+ * commit_iclog. The ctx may be freed by the time we return from
+ * releasing the commit_iclog (i.e. checkpoint has been completed and
+ * callback run) so we can't reference the ctx after the call to
+ * xlog_state_release_iclog().
+ */
+ ticket = ctx->ticket;
/*
* If the checkpoint spans multiple iclogs, wait for all previous iclogs
@@ -1373,12 +1381,14 @@ xlog_cil_push_work(
if (push_commit_stable &&
ctx->commit_iclog->ic_state == XLOG_STATE_ACTIVE)
xlog_state_switch_iclogs(log, ctx->commit_iclog, 0);
- xlog_state_release_iclog(log, ctx->commit_iclog);
+ ticket = ctx->ticket;
+ xlog_state_release_iclog(log, ctx->commit_iclog, ticket);
/* Not safe to reference ctx now! */
spin_unlock(&log->l_icloglock);
xlog_cil_cleanup_whiteouts(&whiteouts);
+ xfs_log_ticket_ungrant(log, ticket);
return;
out_skip:
@@ -1388,17 +1398,19 @@ out_skip:
return;
out_abort_free_ticket:
- xfs_log_ticket_ungrant(log, ctx->ticket);
ASSERT(xlog_is_shutdown(log));
xlog_cil_cleanup_whiteouts(&whiteouts);
if (!ctx->commit_iclog) {
+ xfs_log_ticket_ungrant(log, ctx->ticket);
xlog_cil_committed(ctx);
return;
}
spin_lock(&log->l_icloglock);
- xlog_state_release_iclog(log, ctx->commit_iclog);
+ ticket = ctx->ticket;
+ xlog_state_release_iclog(log, ctx->commit_iclog, ticket);
/* Not safe to reference ctx now! */
spin_unlock(&log->l_icloglock);
+ xfs_log_ticket_ungrant(log, ticket);
}
/*
diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
index d4270a2d4ffb..1bd2963e8fbd 100644
--- a/fs/xfs/xfs_log_priv.h
+++ b/fs/xfs/xfs_log_priv.h
@@ -515,7 +515,8 @@ void xfs_log_ticket_regrant(struct xlog *log, struct xlog_ticket *ticket);
void xlog_state_switch_iclogs(struct xlog *log, struct xlog_in_core *iclog,
int eventual_size);
-int xlog_state_release_iclog(struct xlog *log, struct xlog_in_core *iclog);
+int xlog_state_release_iclog(struct xlog *log, struct xlog_in_core *iclog,
+ struct xlog_ticket *ticket);
/*
* When we crack an atomic LSN, we sample it first so that the value will not