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Arc tuning update #522

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e5b5dd6
Periodically update ARC kstats
Jun 3, 2020
9b84454
zfs: add arc_tuning_update()
tsoome Oct 9, 2025
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71 changes: 66 additions & 5 deletions usr/src/uts/common/fs/zfs/arc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -398,8 +398,8 @@ int arc_zio_arena_free_shift = 2;
/*
* These tunables are for performance analysis.
*/
uint64_t zfs_arc_max;
uint64_t zfs_arc_min;
uint64_t zfs_arc_max = 0;
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@danmcd danmcd Oct 13, 2025

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C defaults to 0 for globals, but I do like the consistency.

uint64_t zfs_arc_min = 0;
uint64_t zfs_arc_meta_limit = 0;
uint64_t zfs_arc_meta_min = 0;
int zfs_arc_grow_retry = 0;
Expand Down Expand Up @@ -796,6 +796,7 @@ static void arc_hdr_alloc_pabd(arc_buf_hdr_t *, int);
static void arc_access(arc_buf_hdr_t *, kmutex_t *);
static boolean_t arc_is_overflowing();
static void arc_buf_watch(arc_buf_t *);
static void arc_tuning_update(void);
static l2arc_dev_t *l2arc_vdev_get(vdev_t *vd);

static arc_buf_contents_t arc_buf_type(arc_buf_hdr_t *);
Expand Down Expand Up @@ -4688,6 +4689,11 @@ arc_kmem_reap_soon(void)
static boolean_t
arc_adjust_cb_check(void *arg, zthr_t *zthr)
{
/*
* While we do not have callbacks to perform tuning updates,
* use this periodic check to call arc_tuning_update().
*/
arc_tuning_update();
/*
* This is necessary in order for the mdb ::arc dcmd to
* show up to date information. Since the ::arc command
Expand Down Expand Up @@ -6971,6 +6977,59 @@ arc_state_multilist_index_func(multilist_t *ml, void *obj)
multilist_get_num_sublists(ml));
}

/*
* Called during module initialization and periodically thereafter to
* apply reasonable changes to the exposed performance tunings. Non-zero
* zfs_* values which differ from the currently set values will be applied.
*/
static void
arc_tuning_update(void)
{
uint64_t allmem = arc_all_memory();

/* Valid range: 32M - <arc_c_max> */
if ((zfs_arc_min) && (zfs_arc_min != arc_c_min) &&
(zfs_arc_min >= 2ULL << SPA_MAXBLOCKSHIFT) &&
(zfs_arc_min <= arc_c_max)) {
arc_c_min = zfs_arc_min;
arc_c = MAX(arc_c, arc_c_min);
}

/* Valid range: 64M - <all physical memory> */
if ((zfs_arc_max) && (zfs_arc_max != arc_c_max) &&
(zfs_arc_max > MIN_ARC_MAX) && (zfs_arc_max < allmem) &&
(zfs_arc_max > arc_c_min)) {
arc_c_max = zfs_arc_max;
arc_c = MIN(arc_c, arc_c_max);
arc_p = (arc_c >> 1);
arc_meta_limit = MIN(arc_meta_limit, arc_c_max);
}

/* Valid range: 16M - <arc_c_max> */
if ((zfs_arc_meta_min) && (zfs_arc_meta_min != arc_meta_min) &&
(zfs_arc_meta_min >= 1ULL << SPA_MAXBLOCKSHIFT) &&
(zfs_arc_meta_min <= arc_c_max)) {
arc_meta_min = zfs_arc_meta_min;
arc_meta_limit = MAX(arc_meta_limit, arc_meta_min);
}

/* Valid range: <arc_meta_min> - <arc_c_max> */
if ((zfs_arc_meta_limit) && (zfs_arc_meta_limit != arc_meta_limit) &&
(zfs_arc_meta_limit >= zfs_arc_meta_min) &&
(zfs_arc_meta_limit <= arc_c_max))
arc_meta_limit = zfs_arc_meta_limit;

/* Valid range: 1 - N */
if (zfs_arc_grow_retry)
arc_grow_retry = zfs_arc_grow_retry;

/* Valid range: 1 - N */
if (zfs_arc_shrink_shift) {
arc_shrink_shift = zfs_arc_shrink_shift;
arc_no_grow_shift = MIN(arc_no_grow_shift, arc_shrink_shift -1);
}
}

static void
arc_state_init(void)
{
Expand Down Expand Up @@ -7099,7 +7158,6 @@ arc_state_fini(void)
aggsum_fini(&astat_hdr_size);
aggsum_fini(&astat_other_size);
aggsum_fini(&astat_l2_hdr_size);

}

uint64_t
Expand Down Expand Up @@ -7202,6 +7260,9 @@ arc_init(void)
if (zfs_arc_p_min_shift > 0)
arc_p_min_shift = zfs_arc_p_min_shift;

/* Apply user specified tunings */
arc_tuning_update();

/* if kmem_flags are set, lets try to use less memory */
if (kmem_debugging())
arc_c = arc_c / 2;
Expand All @@ -7227,8 +7288,8 @@ arc_init(void)
kstat_install(arc_ksp);
}

arc_adjust_zthr = zthr_create(arc_adjust_cb_check,
arc_adjust_cb, NULL);
arc_adjust_zthr = zthr_create_timer(arc_adjust_cb_check,
arc_adjust_cb, NULL, SEC2NSEC(1));
arc_reap_zthr = zthr_create_timer(arc_reap_cb_check,
arc_reap_cb, NULL, SEC2NSEC(1));

Expand Down
7 changes: 7 additions & 0 deletions usr/src/uts/common/fs/zfs/sys/arc.h
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Original file line number Diff line number Diff line change
Expand Up @@ -44,6 +44,13 @@ extern "C" {
*/
#define ARC_EVICT_ALL -1ULL

/*
* ZFS gets very unhappy when the maximum ARC size is smaller than the maximum
* block size and a larger block is written. To leave some safety margin, we
* limit the minimum for zfs_arc_max to the maximium transaction size.
*/
#define MIN_ARC_MAX DMU_MAX_ACCESS

#define HDR_SET_LSIZE(hdr, x) do { \
ASSERT(IS_P2ALIGNED(x, 1U << SPA_MINBLOCKSHIFT)); \
(hdr)->b_lsize = ((x) >> SPA_MINBLOCKSHIFT); \
Expand Down
2 changes: 1 addition & 1 deletion usr/src/uts/common/fs/zfs/sys/dmu.h
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Original file line number Diff line number Diff line change
Expand Up @@ -301,7 +301,7 @@ void zfs_znode_byteswap(void *buf, size_t size);
* The maximum number of bytes that can be accessed as part of one
* operation, including metadata.
*/
#define DMU_MAX_ACCESS (32 * 1024 * 1024) /* 32MB */
#define DMU_MAX_ACCESS (64 * 1024 * 1024) /* 64 */
#define DMU_MAX_DELETEBLKCNT (20480) /* ~5MB of indirect blocks */

#define DMU_USERUSED_OBJECT (-1ULL)
Expand Down