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Support re-prioritizing asynchronous prefetches

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When sequential scrubs were merged, all calls to arc_read()
(including prefetch IOs) were given ZIO_PRIORITY_ASYNC_READ.
Unfortunately, this behaves badly with an existing issue where
prefetch IOs cannot be re-prioritized after the issue. The
result is that synchronous reads end up in the same vdev_queue
as the scrub IOs and can have (in some workloads) multiple
seconds of latency.

This patch incorporates 2 changes. The first ensures that all
scrub IOs are given ZIO_PRIORITY_SCRUB to allow the vdev_queue
code to differentiate between these I/Os and user prefetches.
Second, this patch introduces zio_change_priority() to provide
the missing capability to upgrade a zio's priority.

Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tom Caputi <tcaputi@datto.com>
Closes #6921 
Closes #6926
This commit is contained in:
Tom Caputi
2017-12-21 12:13:06 -05:00
committed by Brian Behlendorf
parent 993669a7bf
commit a8b2e30685
11 changed files with 124 additions and 43 deletions
Download Patch File Download Diff File Expand all files Collapse all files
module/zfs/dsl_scan.c
+4 -4
View File
@@ -1529,7 +1529,7 @@ dsl_scan_prefetch_thread(void *arg)
/* issue the prefetch asynchronously */
(void) arc_read(scn->scn_zio_root, scn->scn_dp->dp_spa,
&spic->spic_bp, dsl_scan_prefetch_cb, spic->spic_spc,
ZIO_PRIORITY_ASYNC_READ, zio_flags, &flags, &spic->spic_zb);
ZIO_PRIORITY_SCRUB, zio_flags, &flags, &spic->spic_zb);
kmem_free(spic, sizeof (scan_prefetch_issue_ctx_t));
}
@@ -1611,7 +1611,7 @@ dsl_scan_recurse(dsl_scan_t *scn, dsl_dataset_t *ds, dmu_objset_type_t ostype,
arc_buf_t *buf;
err = arc_read(NULL, dp->dp_spa, bp, arc_getbuf_func, &buf,
ZIO_PRIORITY_ASYNC_READ, zio_flags, &flags, zb);
ZIO_PRIORITY_SCRUB, zio_flags, &flags, zb);
if (err) {
scn->scn_phys.scn_errors++;
return (err);
@@ -1639,7 +1639,7 @@ dsl_scan_recurse(dsl_scan_t *scn, dsl_dataset_t *ds, dmu_objset_type_t ostype,
}
err = arc_read(NULL, dp->dp_spa, bp, arc_getbuf_func, &buf,
ZIO_PRIORITY_ASYNC_READ, zio_flags, &flags, zb);
ZIO_PRIORITY_SCRUB, zio_flags, &flags, zb);
if (err) {
scn->scn_phys.scn_errors++;
return (err);
@@ -1658,7 +1658,7 @@ dsl_scan_recurse(dsl_scan_t *scn, dsl_dataset_t *ds, dmu_objset_type_t ostype,
arc_buf_t *buf;
err = arc_read(NULL, dp->dp_spa, bp, arc_getbuf_func, &buf,
ZIO_PRIORITY_ASYNC_READ, zio_flags, &flags, zb);
ZIO_PRIORITY_SCRUB, zio_flags, &flags, zb);
if (err) {
scn->scn_phys.scn_errors++;
return (err);