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Implement uncached prefetch

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Previously the primarycache property was handled only in the dbuf
layer. Since the speculative prefetcher is implemented in the ARC,
it had to be disabled for uncacheable buffers.

This change gives the ARC knowledge about uncacheable buffers
via  arc_read() and arc_write(). So when remove_reference() drops
the last reference on the ARC header, it can either immediately destroy
it, or if it is marked as prefetch, put it into a new arc_uncached state. 
That state is scanned every second, evicting stale buffers that were
not demand read.

This change also tracks dbufs that were read from the beginning,
but not to the end.  It is assumed that such buffers may receive further
reads, and so they are stored in dbuf cache. If a following
reads reaches the end of the buffer, it is immediately evicted.
Otherwise it will follow regular dbuf cache eviction.  Since the dbuf
layer does not know actual file sizes, this logic is not applied to
the final buffer of a dnode.

Since uncacheable buffers should no longer stay in the ARC for long,
this patch also tries to optimize I/O by allocating ARC physical
buffers as linear to allow buffer sharing.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: George Wilson <george.wilson@delphix.com>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored by: iXsystems, Inc.
Closes #14243
This commit is contained in:
Alexander Motin
2023-01-04 19:29:54 -05:00
committed by GitHub
parent c935fe2e92
commit ed2f7ba08d
11 changed files with 243 additions and 139 deletions
Download Patch File Download Diff File Expand all files Collapse all files
include/sys/arc_impl.h
+19
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@@ -46,6 +46,7 @@ extern "C" {
* ARC_mru_ghost - recently used, no longer in cache
* ARC_mfu - frequently used, currently cached
* ARC_mfu_ghost - frequently used, no longer in cache
* ARC_uncached - uncacheable prefetch, to be evicted
* ARC_l2c_only - exists in L2ARC but not other states
* When there are no active references to the buffer, they are
* are linked onto a list in one of these arc states. These are
@@ -542,6 +543,7 @@ typedef struct arc_stats {
kstat_named_t arcstat_mru_ghost_hits;
kstat_named_t arcstat_mfu_hits;
kstat_named_t arcstat_mfu_ghost_hits;
kstat_named_t arcstat_uncached_hits;
kstat_named_t arcstat_deleted;
/*
* Number of buffers that could not be evicted because the hash lock
@@ -744,6 +746,21 @@ typedef struct arc_stats {
* ARC_BUFC_METADATA, and linked off the arc_mru_ghost state.
*/
kstat_named_t arcstat_mfu_ghost_evictable_metadata;
/*
* Total number of bytes that are going to be evicted from ARC due to
* ARC_FLAG_UNCACHED being set.
*/
kstat_named_t arcstat_uncached_size;
/*
* Number of data bytes that are going to be evicted from ARC due to
* ARC_FLAG_UNCACHED being set.
*/
kstat_named_t arcstat_uncached_evictable_data;
/*
* Number of metadata bytes that that are going to be evicted from ARC
* due to ARC_FLAG_UNCACHED being set.
*/
kstat_named_t arcstat_uncached_evictable_metadata;
kstat_named_t arcstat_l2_hits;
kstat_named_t arcstat_l2_misses;
/*
@@ -900,6 +917,7 @@ typedef struct arc_sums {
wmsum_t arcstat_mru_ghost_hits;
wmsum_t arcstat_mfu_hits;
wmsum_t arcstat_mfu_ghost_hits;
wmsum_t arcstat_uncached_hits;
wmsum_t arcstat_deleted;
wmsum_t arcstat_mutex_miss;
wmsum_t arcstat_access_skip;
@@ -1006,6 +1024,7 @@ typedef struct arc_evict_waiter {
#define arc_mfu (&ARC_mfu)
#define arc_mfu_ghost (&ARC_mfu_ghost)
#define arc_l2c_only (&ARC_l2c_only)
#define arc_uncached (&ARC_uncached)
extern taskq_t *arc_prune_taskq;
extern arc_stats_t arc_stats;