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Add interface to interface spa_get_worst_case_min_alloc() function

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Provide an interface to retrieve the lowest and highest minimum
allocation size for the normal allocation class.  This can be used
by external consumers of the DMU to estimate potential wasted
capacity when setting the recordsize for an object.

The new "min_alloc" and "max_alloc" keys are added to the pool
configuration and used by default_volblocksize() to warn when
an ineffecient block size is requested.  For older kmods which
don't yet include the new keys fallback to the previous logic.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #17758
This commit is contained in:
Brian Behlendorf
2025-09-25 09:35:35 -07:00
committed by Tony Hutter
parent 3167b0db10
commit 5e10fb6d72
8 changed files with 52 additions and 14 deletions
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cmd/zfs/zfs_main.c
+21 -7
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@@ -912,19 +912,15 @@ usage:
}
/*
* Return a default volblocksize for the pool which always uses more than
* half of the data sectors. This primarily applies to dRAID which always
* writes full stripe widths.
* Calculate the minimum allocation size based on the top-level vdevs.
*/
static uint64_t
default_volblocksize(zpool_handle_t *zhp, nvlist_t *props)
calculate_volblocksize(nvlist_t *config)
{
uint64_t volblocksize, asize = SPA_MINBLOCKSIZE;
uint64_t asize = SPA_MINBLOCKSIZE;
nvlist_t *tree, **vdevs;
uint_t nvdevs;
nvlist_t *config = zpool_get_config(zhp, NULL);
if (nvlist_lookup_nvlist(config, ZPOOL_CONFIG_VDEV_TREE, &tree) != 0 ||
nvlist_lookup_nvlist_array(tree, ZPOOL_CONFIG_CHILDREN,
&vdevs, &nvdevs) != 0) {
@@ -955,6 +951,24 @@ default_volblocksize(zpool_handle_t *zhp, nvlist_t *props)
}
}
return (asize);
}
/*
* Return a default volblocksize for the pool which always uses more than
* half of the data sectors. This primarily applies to dRAID which always
* writes full stripe widths.
*/
static uint64_t
default_volblocksize(zpool_handle_t *zhp, nvlist_t *props)
{
uint64_t volblocksize, asize = SPA_MINBLOCKSIZE;
nvlist_t *config = zpool_get_config(zhp, NULL);
if (nvlist_lookup_uint64(config, ZPOOL_CONFIG_MAX_ALLOC, &asize) != 0)
asize = calculate_volblocksize(config);
/*
* Calculate the target volblocksize such that more than half
* of the asize is used. The following table is for 4k sectors.