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authorDave Chinner <dchinner@redhat.com>2022-07-02 02:12:52 +1000
committerDave Chinner <david@fromorbit.com>2022-07-02 02:12:52 +1000
commit31151cc342dd9cc2c5a5954f3e7b2dcf2fb50f64 (patch)
tree62935586bf2c09b7e68d11812f7680d7201717c3 /fs/xfs/xfs_log.c
parent12380d237b819bd6cf2183f10b55ab47cdaab5e6 (diff)
xfs: rework per-iclog header CIL reservation
For every iclog that a CIL push will use up, we need to ensure we have space reserved for the iclog header in each iclog. It is extremely difficult to do this accurately with a per-cpu counter without expensive summing of the counter in every commit. However, we know what the maximum CIL size is going to be because of the hard space limit we have, and hence we know exactly how many iclogs we are going to need to write out the CIL. We are constrained by the requirement that small transactions only have reservation space for a single iclog header built into them. At commit time we don't know how much of the current transaction reservation is made up of iclog header reservations as calculated by xfs_log_calc_unit_res() when the ticket was reserved. As larger reservations have multiple header spaces reserved, we can steal more than one iclog header reservation at a time, but we only steal the exact number needed for the given log vector size delta. As a result, we don't know exactly when we are going to steal iclog header reservations, nor do we know exactly how many we are going to need for a given CIL. To make things simple, start by calculating the worst case number of iclog headers a full CIL push will require. Record this into an atomic variable in the CIL. Then add a byte counter to the log ticket that records exactly how much iclog header space has been reserved in this ticket by xfs_log_calc_unit_res(). This tells us exactly how much space we can steal from the ticket at transaction commit time. Now, at transaction commit time, we can check if the CIL has a full iclog header reservation and, if not, steal the entire reservation the current ticket holds for iclog headers. This minimises the number of times we need to do atomic operations in the fast path, but still guarantees we get all the reservations we need. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Diffstat (limited to 'fs/xfs/xfs_log.c')
-rw-r--r--fs/xfs/xfs_log.c9
1 files changed, 6 insertions, 3 deletions
diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index ae904b21e9cc..e4416e80a25f 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -3406,7 +3406,8 @@ xfs_log_ticket_get(
static int
xlog_calc_unit_res(
struct xlog *log,
- int unit_bytes)
+ int unit_bytes,
+ int *niclogs)
{
int iclog_space;
uint num_headers;
@@ -3486,6 +3487,8 @@ xlog_calc_unit_res(
/* roundoff padding for transaction data and one for commit record */
unit_bytes += 2 * log->l_iclog_roundoff;
+ if (niclogs)
+ *niclogs = num_headers;
return unit_bytes;
}
@@ -3494,7 +3497,7 @@ xfs_log_calc_unit_res(
struct xfs_mount *mp,
int unit_bytes)
{
- return xlog_calc_unit_res(mp->m_log, unit_bytes);
+ return xlog_calc_unit_res(mp->m_log, unit_bytes, NULL);
}
/*
@@ -3512,7 +3515,7 @@ xlog_ticket_alloc(
tic = kmem_cache_zalloc(xfs_log_ticket_cache, GFP_NOFS | __GFP_NOFAIL);
- unit_res = xlog_calc_unit_res(log, unit_bytes);
+ unit_res = xlog_calc_unit_res(log, unit_bytes, &tic->t_iclog_hdrs);
atomic_set(&tic->t_ref, 1);
tic->t_task = current;