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Add prefetch property

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ZFS prefetch is currently governed by the zfs_prefetch_disable
tunable. However, this is a module-wide settings - if a specific
dataset benefits from prefetch, while others have issue with it,
an optimal solution does not exists.

This commit introduce the "prefetch" tri-state property, which enable
granular control (at dataset/volume level) for prefetching.

This patch does not remove the zfs_prefetch_disable, which remains
a system-wide switch for enable/disable prefetch. However, to avoid
duplication, it would be preferable to deprecate and then remove
the module tunable.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Ameer Hamza <ahamza@ixsystems.com>
Signed-off-by: Gionatan Danti <g.danti@assyoma.it>
Co-authored-by: Gionatan Danti <g.danti@assyoma.it>
Closes #15237 
Closes #15436
This commit is contained in:
Brian Behlendorf
2023-10-24 11:00:07 -07:00
committed by GitHub
parent e57909265b
commit 07345ac252
7 changed files with 63 additions and 2 deletions
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module/zfs/dmu_zfetch.c
+6 -1
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@@ -329,9 +329,14 @@ dmu_zfetch_prepare(zfetch_t *zf, uint64_t blkid, uint64_t nblks,
{
zstream_t *zs;
spa_t *spa = zf->zf_dnode->dn_objset->os_spa;
zfs_prefetch_type_t os_prefetch = zf->zf_dnode->dn_objset->os_prefetch;
if (zfs_prefetch_disable)
if (zfs_prefetch_disable || os_prefetch == ZFS_PREFETCH_NONE)
return (NULL);
if (os_prefetch == ZFS_PREFETCH_METADATA)
fetch_data = B_FALSE;
/*
* If we haven't yet loaded the indirect vdevs' mappings, we
* can only read from blocks that we carefully ensure are on