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Couple minor ARC optimizations.
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Remove unneeded global, practically constant, state pointer variables
(arc_anon, arc_mru, etc.), replacing them with macros of real state
variables addresses (&ARC_anon, &ARC_mru, etc.).  It removes unneeded
(even though usually cached) pointer dereferences from many places.

Change ARC_EVICT_ALL from -1ULL to UINT64_MAX, not requiring special
handling in inner loop of ARC reclamation.  Respectively change bytes
argument of arc_evict_state() from int64_t to uint64_t.

Signed-off-by: Alexander Motin <[email protected]>
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@amotin
amotin committed Jul 11, 2021
1 parent 958826b commit 4505d60
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Showing 3 changed files with 19 additions and 34 deletions.
2 changes: 1 addition & 1 deletion include/sys/arc.h
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Original file line number Diff line number Diff line change
Expand Up @@ -44,7 +44,7 @@ extern "C" {
* Used by arc_flush() to inform arc_evict_state() that it should evict
* all available buffers from the arc state being passed in.
*/
#define ARC_EVICT_ALL -1ULL
#define ARC_EVICT_ALL UINT64_MAX

#define HDR_SET_LSIZE(hdr, x) do { \
ASSERT(IS_P2ALIGNED(x, 1U << SPA_MINBLOCKSHIFT)); \
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11 changes: 9 additions & 2 deletions include/sys/arc_impl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -964,6 +964,13 @@ typedef struct arc_evict_waiter {
#define arc_c_max ARCSTAT(arcstat_c_max) /* max target cache size */
#define arc_sys_free ARCSTAT(arcstat_sys_free) /* target system free bytes */

#define arc_anon (&ARC_anon)
#define arc_mru (&ARC_mru)
#define arc_mru_ghost (&ARC_mru_ghost)
#define arc_mfu (&ARC_mfu)
#define arc_mfu_ghost (&ARC_mfu_ghost)
#define arc_l2c_only (&ARC_l2c_only)

extern taskq_t *arc_prune_taskq;
extern arc_stats_t arc_stats;
extern arc_sums_t arc_sums;
Expand All @@ -974,8 +981,8 @@ extern int arc_no_grow_shift;
extern int arc_shrink_shift;
extern kmutex_t arc_prune_mtx;
extern list_t arc_prune_list;
extern arc_state_t *arc_mfu;
extern arc_state_t *arc_mru;
extern arc_state_t ARC_mfu;
extern arc_state_t ARC_mru;
extern uint_t zfs_arc_pc_percent;
extern int arc_lotsfree_percent;
extern unsigned long zfs_arc_min;
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40 changes: 9 additions & 31 deletions module/zfs/arc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -648,13 +648,6 @@ arc_sums_t arc_sums;
} while (0)

kstat_t *arc_ksp;
static arc_state_t *arc_anon;
static arc_state_t *arc_mru_ghost;
static arc_state_t *arc_mfu_ghost;
static arc_state_t *arc_l2c_only;

arc_state_t *arc_mru;
arc_state_t *arc_mfu;

/*
* There are several ARC variables that are critical to export as kstats --
Expand Down Expand Up @@ -2197,7 +2190,6 @@ arc_evictable_space_increment(arc_buf_hdr_t *hdr, arc_state_t *state)
return;
}

ASSERT(!GHOST_STATE(state));
if (hdr->b_l1hdr.b_pabd != NULL) {
(void) zfs_refcount_add_many(&state->arcs_esize[type],
arc_hdr_size(hdr), hdr);
Expand Down Expand Up @@ -2238,7 +2230,6 @@ arc_evictable_space_decrement(arc_buf_hdr_t *hdr, arc_state_t *state)
return;
}

ASSERT(!GHOST_STATE(state));
if (hdr->b_l1hdr.b_pabd != NULL) {
(void) zfs_refcount_remove_many(&state->arcs_esize[type],
arc_hdr_size(hdr), hdr);
Expand Down Expand Up @@ -4010,23 +4001,21 @@ arc_set_need_free(void)

static uint64_t
arc_evict_state_impl(multilist_t *ml, int idx, arc_buf_hdr_t *marker,
uint64_t spa, int64_t bytes)
uint64_t spa, uint64_t bytes)
{
multilist_sublist_t *mls;
uint64_t bytes_evicted = 0;
arc_buf_hdr_t *hdr;
kmutex_t *hash_lock;
int evict_count = 0;
int evict_count = zfs_arc_evict_batch_limit;

ASSERT3P(marker, !=, NULL);
IMPLY(bytes < 0, bytes == ARC_EVICT_ALL);

mls = multilist_sublist_lock(ml, idx);

for (hdr = multilist_sublist_prev(mls, marker); hdr != NULL;
for (hdr = multilist_sublist_prev(mls, marker); likely(hdr != NULL);
hdr = multilist_sublist_prev(mls, marker)) {
if ((bytes != ARC_EVICT_ALL && bytes_evicted >= bytes) ||
(evict_count >= zfs_arc_evict_batch_limit))
if ((bytes_evicted >= bytes) || (evict_count <= 0))
break;

/*
Expand Down Expand Up @@ -4085,7 +4074,7 @@ arc_evict_state_impl(multilist_t *ml, int idx, arc_buf_hdr_t *marker,
* evict_count in this case.
*/
if (evicted != 0)
evict_count++;
evict_count--;

} else {
ARCSTAT_BUMP(arcstat_mutex_miss);
Expand Down Expand Up @@ -4146,16 +4135,14 @@ arc_evict_state_impl(multilist_t *ml, int idx, arc_buf_hdr_t *marker,
* the given arc state; which is used by arc_flush().
*/
static uint64_t
arc_evict_state(arc_state_t *state, uint64_t spa, int64_t bytes,
arc_evict_state(arc_state_t *state, uint64_t spa, uint64_t bytes,
arc_buf_contents_t type)
{
uint64_t total_evicted = 0;
multilist_t *ml = &state->arcs_list[type];
int num_sublists;
arc_buf_hdr_t **markers;

IMPLY(bytes < 0, bytes == ARC_EVICT_ALL);

num_sublists = multilist_get_num_sublists(ml);

/*
Expand Down Expand Up @@ -4187,7 +4174,7 @@ arc_evict_state(arc_state_t *state, uint64_t spa, int64_t bytes,
* While we haven't hit our target number of bytes to evict, or
* we're evicting all available buffers.
*/
while (total_evicted < bytes || bytes == ARC_EVICT_ALL) {
while (total_evicted < bytes) {
int sublist_idx = multilist_get_random_index(ml);
uint64_t scan_evicted = 0;

Expand Down Expand Up @@ -4215,9 +4202,7 @@ arc_evict_state(arc_state_t *state, uint64_t spa, int64_t bytes,
uint64_t bytes_remaining;
uint64_t bytes_evicted;

if (bytes == ARC_EVICT_ALL)
bytes_remaining = ARC_EVICT_ALL;
else if (total_evicted < bytes)
if (total_evicted < bytes)
bytes_remaining = bytes - total_evicted;
else
break;
Expand Down Expand Up @@ -4312,7 +4297,7 @@ static uint64_t
arc_evict_impl(arc_state_t *state, uint64_t spa, int64_t bytes,
arc_buf_contents_t type)
{
int64_t delta;
uint64_t delta;

if (bytes > 0 && zfs_refcount_count(&state->arcs_esize[type]) > 0) {
delta = MIN(zfs_refcount_count(&state->arcs_esize[type]),
Expand Down Expand Up @@ -7563,13 +7548,6 @@ arc_tuning_update(boolean_t verbose)
static void
arc_state_init(void)
{
arc_anon = &ARC_anon;
arc_mru = &ARC_mru;
arc_mru_ghost = &ARC_mru_ghost;
arc_mfu = &ARC_mfu;
arc_mfu_ghost = &ARC_mfu_ghost;
arc_l2c_only = &ARC_l2c_only;

multilist_create(&arc_mru->arcs_list[ARC_BUFC_METADATA],
sizeof (arc_buf_hdr_t),
offsetof(arc_buf_hdr_t, b_l1hdr.b_arc_node),
Expand Down

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