Prune metadata from ghost lists in arc_adjust_meta

To maintain a strict limit on the metadata contained in the arc, while
preventing the arc buffer headers from completely consuming the
"arc_meta_used" space, we need to evict metadata buffers from the arc's
ghost lists along with the regular lists.

This change modifies arc_adjust_meta such that it more closely models
the adjustments made in arc_adjust. "arc_meta_used" is used similarly to
"arc_size", and "arc_meta_limit" is used similarly to "arc_c".

Testing metadata intensive workloads (e.g. creating, copying, and
removing millions of small files and/or directories) has shown this
change to make a dramatic improvement to the hit rate maintained in the
arc. While I think there is still room for improvement, this is a big
step in the right direction.

In addition, zpl_free_cached_objects was made into a no-op as I'm not
yet sure how to properly implement that function.

Signed-off-by: Prakash Surya <surya1@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #2110
This commit is contained in:
Prakash Surya 2014-01-03 11:40:52 -08:00 committed by Brian Behlendorf
parent 1e3cb67b53
commit 94520ca462
3 changed files with 49 additions and 21 deletions

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@ -160,7 +160,6 @@ void arc_freed(spa_t *spa, const blkptr_t *bp);
void arc_set_callback(arc_buf_t *buf, arc_evict_func_t *func, void *private); void arc_set_callback(arc_buf_t *buf, arc_evict_func_t *func, void *private);
int arc_buf_evict(arc_buf_t *buf); int arc_buf_evict(arc_buf_t *buf);
void arc_adjust_meta(int64_t adjustment, boolean_t may_prune);
void arc_flush(spa_t *spa); void arc_flush(spa_t *spa);
void arc_tempreserve_clear(uint64_t reserve); void arc_tempreserve_clear(uint64_t reserve);
int arc_tempreserve_space(uint64_t reserve, uint64_t txg); int arc_tempreserve_space(uint64_t reserve, uint64_t txg);

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@ -2268,24 +2268,61 @@ arc_do_user_evicts(void)
* This is only used to enforce the tunable arc_meta_limit, if we are * This is only used to enforce the tunable arc_meta_limit, if we are
* unable to evict enough buffers notify the user via the prune callback. * unable to evict enough buffers notify the user via the prune callback.
*/ */
void static void
arc_adjust_meta(int64_t adjustment, boolean_t may_prune) arc_adjust_meta(void)
{ {
int64_t delta; int64_t adjustmnt, delta;
if (adjustment > 0 && arc_mru->arcs_lsize[ARC_BUFC_METADATA] > 0) { /*
delta = MIN(arc_mru->arcs_lsize[ARC_BUFC_METADATA], adjustment); * This slightly differs than the way we evict from the mru in
* arc_adjust because we don't have a "target" value (i.e. no
* "meta" arc_p). As a result, I think we can completely
* cannibalize the metadata in the MRU before we evict the
* metadata from the MFU. I think we probably need to implement a
* "metadata arc_p" value to do this properly.
*/
adjustmnt = arc_meta_used - arc_meta_limit;
if (adjustmnt > 0 && arc_mru->arcs_lsize[ARC_BUFC_METADATA] > 0) {
delta = MIN(arc_mru->arcs_lsize[ARC_BUFC_METADATA], adjustmnt);
arc_evict(arc_mru, 0, delta, FALSE, ARC_BUFC_METADATA); arc_evict(arc_mru, 0, delta, FALSE, ARC_BUFC_METADATA);
adjustment -= delta; adjustmnt -= delta;
} }
if (adjustment > 0 && arc_mfu->arcs_lsize[ARC_BUFC_METADATA] > 0) { /*
delta = MIN(arc_mfu->arcs_lsize[ARC_BUFC_METADATA], adjustment); * We can't afford to recalculate adjustmnt here. If we do,
* new metadata buffers can sneak into the MRU or ANON lists,
* thus penalize the MFU metadata. Although the fudge factor is
* small, it has been empirically shown to be significant for
* certain workloads (e.g. creating many empty directories). As
* such, we use the original calculation for adjustmnt, and
* simply decrement the amount of data evicted from the MRU.
*/
if (adjustmnt > 0 && arc_mfu->arcs_lsize[ARC_BUFC_METADATA] > 0) {
delta = MIN(arc_mfu->arcs_lsize[ARC_BUFC_METADATA], adjustmnt);
arc_evict(arc_mfu, 0, delta, FALSE, ARC_BUFC_METADATA); arc_evict(arc_mfu, 0, delta, FALSE, ARC_BUFC_METADATA);
adjustment -= delta;
} }
if (may_prune && (adjustment > 0) && (arc_meta_used > arc_meta_limit)) adjustmnt = arc_mru->arcs_lsize[ARC_BUFC_METADATA] +
arc_mru_ghost->arcs_lsize[ARC_BUFC_METADATA] - arc_meta_limit;
if (adjustmnt > 0 && arc_mru_ghost->arcs_lsize[ARC_BUFC_METADATA] > 0) {
delta = MIN(adjustmnt,
arc_mru_ghost->arcs_lsize[ARC_BUFC_METADATA]);
arc_evict_ghost(arc_mru_ghost, 0, delta, ARC_BUFC_METADATA);
}
adjustmnt = arc_mru_ghost->arcs_lsize[ARC_BUFC_METADATA] +
arc_mfu_ghost->arcs_lsize[ARC_BUFC_METADATA] - arc_meta_limit;
if (adjustmnt > 0 && arc_mfu_ghost->arcs_lsize[ARC_BUFC_METADATA] > 0) {
delta = MIN(adjustmnt,
arc_mfu_ghost->arcs_lsize[ARC_BUFC_METADATA]);
arc_evict_ghost(arc_mfu_ghost, 0, delta, ARC_BUFC_METADATA);
}
if (arc_meta_used > arc_meta_limit)
arc_do_user_prune(zfs_arc_meta_prune); arc_do_user_prune(zfs_arc_meta_prune);
} }
@ -2405,7 +2442,6 @@ static void
arc_adapt_thread(void) arc_adapt_thread(void)
{ {
callb_cpr_t cpr; callb_cpr_t cpr;
int64_t prune;
CALLB_CPR_INIT(&cpr, &arc_reclaim_thr_lock, callb_generic_cpr, FTAG); CALLB_CPR_INIT(&cpr, &arc_reclaim_thr_lock, callb_generic_cpr, FTAG);
@ -2441,14 +2477,7 @@ arc_adapt_thread(void)
if (arc_no_grow && ddi_get_lbolt() >= arc_grow_time) if (arc_no_grow && ddi_get_lbolt() >= arc_grow_time)
arc_no_grow = FALSE; arc_no_grow = FALSE;
/* arc_adjust_meta();
* Keep meta data usage within limits, arc_shrink() is not
* used to avoid collapsing the arc_c value when only the
* arc_meta_limit is being exceeded.
*/
prune = (int64_t)arc_meta_used - (int64_t)arc_meta_limit;
if (prune > 0)
arc_adjust_meta(prune, B_TRUE);
arc_adjust(); arc_adjust();

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@ -342,7 +342,7 @@ zpl_nr_cached_objects(struct super_block *sb)
static void static void
zpl_free_cached_objects(struct super_block *sb, int nr_to_scan) zpl_free_cached_objects(struct super_block *sb, int nr_to_scan)
{ {
arc_adjust_meta(nr_to_scan * sizeof (znode_t), B_FALSE); /* noop */
} }
#endif /* HAVE_FREE_CACHED_OBJECTS */ #endif /* HAVE_FREE_CACHED_OBJECTS */