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Add l2arc_max_block_size tunable 

Set a limit for the largest compressed block which can be written
to an L2ARC device.  By default this limit is set to 16M so there
is no change in behavior.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Richard Elling <Richard.Elling@RichardElling.com>
Signed-off-by: Tim Chase <tim@chase2k.com>
Closes #4323
This commit is contained in:
Brian Behlendorf 2016-02-10 10:42:01 -08:00
parent 5428dc51fb
commit 8a09d5fd46
2 changed files with 47 additions and 1 deletions
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14
man/man5/zfs-module-parameters.5
View File

@ -79,6 +79,20 @@ Compressed l2arc_headroom multiplier
Default value: \fB200\fR.
.RE
.sp
.ne 2
.na
\fBl2arc_max_block_size\fR (ulong)
.ad
.RS 12n
The maximum block size which may be written to an L2ARC device, after
compression and other factors. This setting is used to prevent a small
number of large blocks from pushing a larger number of small blocks out
of the cache.
.sp
Default value: \fB16,777,216\fR.
.RE
.sp
.ne 2
.na

34
module/zfs/arc.c
View File

@ -446,6 +446,7 @@ typedef struct arc_stats {
kstat_named_t arcstat_l2_writes_done;
kstat_named_t arcstat_l2_writes_error;
kstat_named_t arcstat_l2_writes_lock_retry;
kstat_named_t arcstat_l2_writes_skip_toobig;
kstat_named_t arcstat_l2_evict_lock_retry;
kstat_named_t arcstat_l2_evict_reading;
kstat_named_t arcstat_l2_evict_l1cached;
@ -542,6 +543,7 @@ static arc_stats_t arc_stats = {
{ "l2_writes_done", KSTAT_DATA_UINT64 },
{ "l2_writes_error", KSTAT_DATA_UINT64 },
{ "l2_writes_lock_retry", KSTAT_DATA_UINT64 },
{ "l2_writes_skip_toobig", KSTAT_DATA_UINT64 },
{ "l2_evict_lock_retry", KSTAT_DATA_UINT64 },
{ "l2_evict_reading", KSTAT_DATA_UINT64 },
{ "l2_evict_l1cached", KSTAT_DATA_UINT64 },
@ -726,6 +728,8 @@ uint64_t zfs_crc64_table[256];
#define L2ARC_WRITE_SIZE (8 * 1024 * 1024) /* initial write max */
#define L2ARC_HEADROOM 2 /* num of writes */
#define L2ARC_MAX_BLOCK_SIZE (16 * 1024 * 1024) /* max compress size */
/*
* If we discover during ARC scan any buffers to be compressed, we boost
* our headroom for the next scanning cycle by this percentage multiple.
@ -734,6 +738,7 @@ uint64_t zfs_crc64_table[256];
#define L2ARC_FEED_SECS 1 /* caching interval secs */
#define L2ARC_FEED_MIN_MS 200 /* min caching interval ms */
/*
* Used to distinguish headers that are being process by
* l2arc_write_buffers(), but have yet to be assigned to a l2arc disk
@ -752,6 +757,7 @@ unsigned long l2arc_write_max = L2ARC_WRITE_SIZE; /* def max write size */
unsigned long l2arc_write_boost = L2ARC_WRITE_SIZE; /* extra warmup write */
unsigned long l2arc_headroom = L2ARC_HEADROOM; /* # of dev writes */
unsigned long l2arc_headroom_boost = L2ARC_HEADROOM_BOOST;
unsigned long l2arc_max_block_size = L2ARC_MAX_BLOCK_SIZE;
unsigned long l2arc_feed_secs = L2ARC_FEED_SECS; /* interval seconds */
unsigned long l2arc_feed_min_ms = L2ARC_FEED_MIN_MS; /* min interval msecs */
int l2arc_noprefetch = B_TRUE; /* don't cache prefetch bufs */
@ -6020,7 +6026,20 @@ top:
*/
l2arc_release_cdata_buf(hdr);
if (zio->io_error != 0) {
/*
* Skipped - drop L2ARC entry and mark the header as no
* longer L2 eligibile.
*/
if (hdr->b_l2hdr.b_daddr == L2ARC_ADDR_UNSET) {
list_remove(buflist, hdr);
hdr->b_flags &= ~ARC_FLAG_HAS_L2HDR;
hdr->b_flags &= ~ARC_FLAG_L2CACHE;
ARCSTAT_BUMP(arcstat_l2_writes_skip_toobig);
(void) refcount_remove_many(&dev->l2ad_alloc,
hdr->b_l2hdr.b_asize, hdr);
} else if (zio->io_error != 0) {
/*
* Error - drop L2ARC entry.
*/
@ -6567,6 +6586,16 @@ l2arc_write_buffers(spa_t *spa, l2arc_dev_t *dev, uint64_t target_sz,
if (buf_sz != 0) {
uint64_t buf_a_sz;
/*
* Buffers which are larger than l2arc_max_block_size
* after compression are skipped and removed from L2
* eligibility.
*/
if (buf_sz > l2arc_max_block_size) {
hdr->b_l2hdr.b_daddr = L2ARC_ADDR_UNSET;
continue;
}
wzio = zio_write_phys(pio, dev->l2ad_vdev,
dev->l2ad_hand, buf_sz, buf_data, ZIO_CHECKSUM_OFF,
NULL, NULL, ZIO_PRIORITY_ASYNC_WRITE,
@ -7129,6 +7158,9 @@ MODULE_PARM_DESC(l2arc_headroom, "Number of max device writes to precache");
module_param(l2arc_headroom_boost, ulong, 0644);
MODULE_PARM_DESC(l2arc_headroom_boost, "Compressed l2arc_headroom multiplier");
module_param(l2arc_max_block_size, ulong, 0644);
MODULE_PARM_DESC(l2arc_max_block_size, "Skip L2ARC buffers larger than N");
module_param(l2arc_feed_secs, ulong, 0644);
MODULE_PARM_DESC(l2arc_feed_secs, "Seconds between L2ARC writing");