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Increase L2ARC write rate and headroom 

Current L2ARC write rate and headroom parameters are very conservative:
l2arc_write_max=8M and l2arc_headroom=2 (ie: a full L2ARC writes at
8 MB/s, scanning 16/32 MB of ARC tail each time; a warming L2ARC runs
at 2x these rates).

These values were selected 15+ years ago based on then-current SSDs
size, performance and endurance. Today we have multi-TB, fast and
cheap SSDs which can sustain much higher read/write rates.

For this reason, this patch increases l2arc_write_max to 32M and
l2arc_headroom to 8 (4x increase for both).

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Gionatan Danti <g.danti@assyoma.it>
Closes #15457
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shodanshok 2023-11-09 01:30:47 +01:00 committed by GitHub
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2 changed files with 5 additions and 5 deletions
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6
man/man4/zfs.4
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@ -97,7 +97,7 @@ and only applicable in related situations.
.It Sy l2arc_feed_secs Ns = Ns Sy 1 Pq u64
Seconds between L2ARC writing.
.
.It Sy l2arc_headroom Ns = Ns Sy 2 Pq u64
.It Sy l2arc_headroom Ns = Ns Sy 8 Pq u64
How far through the ARC lists to search for L2ARC cacheable content,
expressed as a multiplier of
.Sy l2arc_write_max .
@ -200,12 +200,12 @@ to enable caching/reading prefetches to/from L2ARC.
.It Sy l2arc_norw Ns = Ns Sy 0 Ns | Ns 1 Pq int
No reads during writes.
.
.It Sy l2arc_write_boost Ns = Ns Sy 8388608 Ns B Po 8 MiB Pc Pq u64
.It Sy l2arc_write_boost Ns = Ns Sy 33554432 Ns B Po 32 MiB Pc Pq u64
Cold L2ARC devices will have
.Sy l2arc_write_max
increased by this amount while they remain cold.
.
.It Sy l2arc_write_max Ns = Ns Sy 8388608 Ns B Po 8 MiB Pc Pq u64
.It Sy l2arc_write_max Ns = Ns Sy 33554432 Ns B Po 32 MiB Pc Pq u64
Max write bytes per interval.
.
.It Sy l2arc_rebuild_enabled Ns = Ns Sy 1 Ns | Ns 0 Pq int

4
module/zfs/arc.c
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@ -776,8 +776,8 @@ uint64_t zfs_crc64_table[256];
* Level 2 ARC
*/
#define L2ARC_WRITE_SIZE (8 * 1024 * 1024) /* initial write max */
#define L2ARC_HEADROOM 2 /* num of writes */
#define L2ARC_WRITE_SIZE (32 * 1024 * 1024) /* initial write max */
#define L2ARC_HEADROOM 8 /* num of writes */
/*
* If we discover during ARC scan any buffers to be compressed, we boost