Update arc_available_memory() to check freemem
While Linux doesn't provide detailed information about the state of
the VM it does provide us total free pages. This information should
be incorporated in to the arc_available_memory() calculation rather
than solely relying on a signal from direct reclaim. Conceptually
this brings arc_available_memory() back in sync with illumos.
It is also desirable that the target amount of free memory be tunable
on a system. While the default values are expected to work well
for most workloads there may be cases where custom values are needed.
The zfs_arc_sys_free module option was added for this purpose.
zfs_arc_sys_free - The target number of bytes the ARC should leave
as free memory on the system. This value can
checked in /proc/spl/kstat/zfs/arcstats and
setting this module option will override the
default value.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #3637
This commit is contained in:
Brian Behlendorf
parent
6339c1b9dc
commit
11f552fa90
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@ -566,6 +566,19 @@ log2(fraction of arc to reclaim)
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Default value: \fB5\fR.
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.RE
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.sp
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.ne 2
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.na
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\fBzfs_arc_sys_free\fR (ulong)
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.ad
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.RS 12n
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The target number of bytes the ARC should leave as free memory on the system.
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Defaults to the larger of 1/64 of physical memory or 512K. Setting this
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option to a non-zero value will override the default.
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.sp
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Default value: \fB0\fR.
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.RE
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.sp
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.ne 2
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.na
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@ -240,6 +240,7 @@ int zfs_arc_average_blocksize = 8 * 1024; /* 8KB */
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/*
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* These tunables are Linux specific
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*/
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unsigned long zfs_arc_sys_free = 0;
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int zfs_arc_memory_throttle_disable = 1;
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int zfs_arc_min_prefetch_lifespan = 0;
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int zfs_arc_p_aggressive_disable = 1;
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@ -473,6 +474,8 @@ typedef struct arc_stats {
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kstat_named_t arcstat_meta_limit;
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kstat_named_t arcstat_meta_max;
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kstat_named_t arcstat_meta_min;
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kstat_named_t arcstat_need_free;
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kstat_named_t arcstat_sys_free;
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} arc_stats_t;
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static arc_stats_t arc_stats = {
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@ -564,7 +567,9 @@ static arc_stats_t arc_stats = {
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{ "arc_meta_used", KSTAT_DATA_UINT64 },
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{ "arc_meta_limit", KSTAT_DATA_UINT64 },
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{ "arc_meta_max", KSTAT_DATA_UINT64 },
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{ "arc_meta_min", KSTAT_DATA_UINT64 }
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{ "arc_meta_min", KSTAT_DATA_UINT64 },
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{ "arc_need_free", KSTAT_DATA_UINT64 },
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{ "arc_sys_free", KSTAT_DATA_UINT64 }
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};
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#define ARCSTAT(stat) (arc_stats.stat.value.ui64)
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@ -633,6 +638,8 @@ static arc_state_t *arc_l2c_only;
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#define arc_meta_min ARCSTAT(arcstat_meta_min) /* min size for metadata */
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#define arc_meta_used ARCSTAT(arcstat_meta_used) /* size of metadata */
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#define arc_meta_max ARCSTAT(arcstat_meta_max) /* max size of metadata */
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#define arc_need_free ARCSTAT(arcstat_need_free) /* bytes to be freed */
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#define arc_sys_free ARCSTAT(arcstat_sys_free) /* target system free bytes */
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#define L2ARC_IS_VALID_COMPRESS(_c_) \
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((_c_) == ZIO_COMPRESS_LZ4 || (_c_) == ZIO_COMPRESS_EMPTY)
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@ -3222,12 +3229,6 @@ int64_t last_free_memory;
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free_memory_reason_t last_free_reason;
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#ifdef _KERNEL
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#ifdef __linux__
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/*
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* expiration time for arc_no_grow set by direct memory reclaim.
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*/
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static clock_t arc_grow_time = 0;
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#else
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/*
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* Additional reserve of pages for pp_reserve.
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*/
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@ -3237,7 +3238,6 @@ int64_t arc_pages_pp_reserve = 64;
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* Additional reserve of pages for swapfs.
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*/
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int64_t arc_swapfs_reserve = 64;
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#endif
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#endif /* _KERNEL */
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/*
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@ -3250,26 +3250,14 @@ arc_available_memory(void)
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{
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int64_t lowest = INT64_MAX;
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free_memory_reason_t r = FMR_UNKNOWN;
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#ifdef _KERNEL
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#ifdef __linux__
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/*
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* Under Linux we are not allowed to directly interrogate the global
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* memory state. Instead rely on observing that direct reclaim has
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* recently occurred therefore the system must be low on memory. The
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* exact values returned are not critical but should be small.
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*/
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if (ddi_time_after_eq(ddi_get_lbolt(), arc_grow_time))
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lowest = PAGE_SIZE;
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else
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lowest = -PAGE_SIZE;
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#else
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int64_t n;
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#ifdef __linux__
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pgcnt_t needfree = btop(arc_need_free);
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pgcnt_t lotsfree = btop(arc_sys_free);
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pgcnt_t desfree = 0;
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#endif
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/*
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* Platforms like illumos have greater visibility in to the memory
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* subsystem and can return a more detailed analysis of memory.
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*/
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if (needfree > 0) {
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n = PAGESIZE * (-needfree);
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if (n < lowest) {
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@ -3291,6 +3279,7 @@ arc_available_memory(void)
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r = FMR_LOTSFREE;
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}
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#ifndef __linux__
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/*
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* check to make sure that swapfs has enough space so that anon
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* reservations can still succeed. anon_resvmem() checks that the
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@ -3319,6 +3308,7 @@ arc_available_memory(void)
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lowest = n;
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r = FMR_PAGES_PP_MAXIMUM;
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}
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#endif
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#if defined(__i386)
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/*
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@ -3357,12 +3347,11 @@ arc_available_memory(void)
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r = FMR_ZIO_ARENA;
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}
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}
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#endif /* __linux__ */
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#else
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#else /* _KERNEL */
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/* Every 100 calls, free a small amount */
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if (spa_get_random(100) == 0)
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lowest = -1024;
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#endif
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#endif /* _KERNEL */
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last_free_memory = lowest;
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last_free_reason = r;
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@ -3480,7 +3469,7 @@ arc_reclaim_thread(void)
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to_free = (arc_c >> arc_shrink_shift) - free_memory;
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if (to_free > 0) {
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#ifdef _KERNEL
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to_free = MAX(to_free, ptob(needfree));
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to_free = MAX(to_free, arc_need_free);
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#endif
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arc_shrink(to_free);
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}
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@ -3507,9 +3496,11 @@ arc_reclaim_thread(void)
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/*
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* We're either no longer overflowing, or we
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* can't evict anything more, so we should wake
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* up any threads before we go to sleep.
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* up any threads before we go to sleep and clear
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* arc_need_free since nothing more can be done.
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*/
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cv_broadcast(&arc_reclaim_waiters_cv);
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arc_need_free = 0;
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/*
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* Block until signaled, or after one second (we
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@ -3713,7 +3704,7 @@ __arc_shrinker_func(struct shrinker *shrink, struct shrink_control *sc)
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ARCSTAT_BUMP(arcstat_memory_indirect_count);
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} else {
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arc_no_grow = B_TRUE;
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arc_grow_time = ddi_get_lbolt() + (zfs_arc_grow_retry * hz);
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arc_need_free = ptob(sc->nr_to_scan);
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ARCSTAT_BUMP(arcstat_memory_direct_count);
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}
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@ -5288,6 +5279,10 @@ arc_tuning_update(void)
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/* Valid range: 1 - N ticks */
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if (zfs_arc_min_prefetch_lifespan)
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arc_min_prefetch_lifespan = zfs_arc_min_prefetch_lifespan;
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/* Valid range: 0 - <all physical memory> */
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if ((zfs_arc_sys_free) && (zfs_arc_sys_free != arc_sys_free))
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arc_sys_free = MIN(MAX(zfs_arc_sys_free, 0), ptob(physmem));
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}
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void
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@ -5329,6 +5324,10 @@ arc_init(void)
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* swapping out pages when it is preferable to shrink the arc.
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*/
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spl_register_shrinker(&arc_shrinker);
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/* Set to 1/64 of all memory or a minimum of 512K */
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arc_sys_free = MAX(ptob(physmem / 64), (512 * 1024));
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arc_need_free = 0;
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#endif
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/* Set min cache to allow safe operation of arc_adapt() */
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@ -7064,4 +7063,7 @@ MODULE_PARM_DESC(l2arc_feed_again, "Turbo L2ARC warmup");
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module_param(l2arc_norw, int, 0644);
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MODULE_PARM_DESC(l2arc_norw, "No reads during writes");
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module_param(zfs_arc_sys_free, ulong, 0644);
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MODULE_PARM_DESC(zfs_arc_sys_free, "System free memory target size in bytes");
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#endif
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