diff options
| -rw-r--r-- | fs/xfs/xfs_log_priv.h | 29 |
1 files changed, 23 insertions, 6 deletions
diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h index f4a54469d7d0..938edd19a8a6 100644 --- a/fs/xfs/xfs_log_priv.h +++ b/fs/xfs/xfs_log_priv.h @@ -316,13 +316,30 @@ struct xfs_cil { * tries to keep 25% of the log free, so we need to keep below that limit or we * risk running out of free log space to start any new transactions. * - * In order to keep background CIL push efficient, we will set a lower - * threshold at which background pushing is attempted without blocking current - * transaction commits. A separate, higher bound defines when CIL pushes are - * enforced to ensure we stay within our maximum checkpoint size bounds. - * threshold, yet give us plenty of space for aggregation on large logs. + * In order to keep background CIL push efficient, we only need to ensure the + * CIL is large enough to maintain sufficient in-memory relogging to avoid + * repeated physical writes of frequently modified metadata. If we allow the CIL + * to grow to a substantial fraction of the log, then we may be pinning hundreds + * of megabytes of metadata in memory until the CIL flushes. This can cause + * issues when we are running low on memory - pinned memory cannot be reclaimed, + * and the CIL consumes a lot of memory. Hence we need to set an upper physical + * size limit for the CIL that limits the maximum amount of memory pinned by the + * CIL but does not limit performance by reducing relogging efficiency + * significantly. + * + * As such, the CIL push threshold ends up being the smaller of two thresholds: + * - a threshold large enough that it allows CIL to be pushed and progress to be + * made without excessive blocking of incoming transaction commits. This is + * defined to be 12.5% of the log space - half the 25% push threshold of the + * AIL. + * - small enough that it doesn't pin excessive amounts of memory but maintains + * close to peak relogging efficiency. This is defined to be 16x the iclog + * buffer window (32MB) as measurements have shown this to be roughly the + * point of diminishing performance increases under highly concurrent + * modification workloads. */ -#define XLOG_CIL_SPACE_LIMIT(log) (log->l_logsize >> 3) +#define XLOG_CIL_SPACE_LIMIT(log) \ + min_t(int, (log)->l_logsize >> 3, BBTOB(XLOG_TOTAL_REC_SHIFT(log)) << 4) /* * ticket grant locks, queues and accounting have their own cachlines |