From 25d232f40713604dec1f6f6ef68802ab58115af0 Mon Sep 17 00:00:00 2001 From: chrisrd Date: Sat, 30 Sep 2017 08:49:19 +1000 Subject: [PATCH] Scale the dbuf cache with arc_c Commit d3c2ae1 introduced a dbuf cache with a default size of the minimum of 100M or 1/32 maximum ARC size. (These figures may be adjusted using dbuf_cache_max_bytes and dbuf_cache_max_shift.) The dbuf cache is counted as metadata for the purposes of ARC size calculations. On a 1GB box the ARC maximum size defaults to c_max 493M which gives a dbuf cache default minimum size of 15.4M, and the ARC metadata defaults to minimum 16M. I.e. the dbuf cache is an significant proportion of the minimum metadata size. With other overheads involved this actually means the ARC metadata doesn't get down to the minimum. This patch dynamically scales the dbuf cache to the target ARC size instead of statically scaling it to the maximum ARC size. (The scale is still set by dbuf_cache_max_shift and the maximum size is still fixed by dbuf_cache_max_bytes.) Using the target ARC size rather than the current ARC size is done to help the ARC reach the target rather than simply focusing on the current size. Reviewed-by: Chunwei Chen Reviewed-by: Brian Behlendorf Reviewed-by: George Melikov Signed-off-by: Chris Dunlop Issue #6506 Closes #6561 --- include/sys/arc.h | 2 +- module/zfs/arc.c | 4 ++-- module/zfs/dbuf.c | 23 +++++++++++++++++------ 3 files changed, 20 insertions(+), 9 deletions(-) diff --git a/include/sys/arc.h b/include/sys/arc.h index 07a72302df..66f37cf710 100644 --- a/include/sys/arc.h +++ b/include/sys/arc.h @@ -248,7 +248,7 @@ void arc_flush(spa_t *spa, boolean_t retry); void arc_tempreserve_clear(uint64_t reserve); int arc_tempreserve_space(uint64_t reserve, uint64_t txg); -uint64_t arc_max_bytes(void); +uint64_t arc_target_bytes(void); void arc_init(void); void arc_fini(void); diff --git a/module/zfs/arc.c b/module/zfs/arc.c index 0a09c443b0..d678b335cf 100644 --- a/module/zfs/arc.c +++ b/module/zfs/arc.c @@ -6475,9 +6475,9 @@ arc_state_fini(void) } uint64_t -arc_max_bytes(void) +arc_target_bytes(void) { - return (arc_c_max); + return (arc_c); } void diff --git a/module/zfs/dbuf.c b/module/zfs/dbuf.c index dc2c00495b..62340469d3 100644 --- a/module/zfs/dbuf.c +++ b/module/zfs/dbuf.c @@ -464,24 +464,35 @@ dbuf_cache_multilist_index_func(multilist_t *ml, void *obj) multilist_get_num_sublists(ml)); } +static inline unsigned long +dbuf_cache_target_bytes(void) +{ + return MIN(dbuf_cache_max_bytes, + arc_target_bytes() >> dbuf_cache_max_shift); +} + static inline boolean_t dbuf_cache_above_hiwater(void) { + uint64_t dbuf_cache_target = dbuf_cache_target_bytes(); + uint64_t dbuf_cache_hiwater_bytes = - (dbuf_cache_max_bytes * dbuf_cache_hiwater_pct) / 100; + (dbuf_cache_target * dbuf_cache_hiwater_pct) / 100; return (refcount_count(&dbuf_cache_size) > - dbuf_cache_max_bytes + dbuf_cache_hiwater_bytes); + dbuf_cache_target + dbuf_cache_hiwater_bytes); } static inline boolean_t dbuf_cache_above_lowater(void) { + uint64_t dbuf_cache_target = dbuf_cache_target_bytes(); + uint64_t dbuf_cache_lowater_bytes = - (dbuf_cache_max_bytes * dbuf_cache_lowater_pct) / 100; + (dbuf_cache_target * dbuf_cache_lowater_pct) / 100; return (refcount_count(&dbuf_cache_size) > - dbuf_cache_max_bytes - dbuf_cache_lowater_bytes); + dbuf_cache_target - dbuf_cache_lowater_bytes); } /* @@ -601,7 +612,7 @@ dbuf_evict_notify(void) * because it's OK to occasionally make the wrong decision here, * and grabbing the lock results in massive lock contention. */ - if (refcount_count(&dbuf_cache_size) > dbuf_cache_max_bytes) { + if (refcount_count(&dbuf_cache_size) > dbuf_cache_target_bytes()) { if (dbuf_cache_above_hiwater()) dbuf_evict_one(); cv_signal(&dbuf_evict_cv); @@ -658,7 +669,7 @@ retry: * dbuf cache to 1/32nd (default) of the size of the ARC. */ dbuf_cache_max_bytes = MIN(dbuf_cache_max_bytes, - arc_max_bytes() >> dbuf_cache_max_shift); + arc_target_bytes() >> dbuf_cache_max_shift); /* * All entries are queued via taskq_dispatch_ent(), so min/maxalloc