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Correct weight recalculation of space-based metaslabs #17531

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Merged
merged 2 commits into from
Jul 16, 2025
Merged

Correct weight recalculation of space-based metaslabs #17531

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Correct weight recalculation of space-based metaslabs
Jul 9, 2025
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Jul 10, 2025
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34 changes: 7 additions & 27 deletions module/zfs/metaslab.c
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Original file line number Diff line number Diff line change
Expand Up @@ -5199,29 +5199,16 @@ metaslab_group_alloc(metaslab_group_t *mg, zio_alloc_list_t *zal,

/*
* We were unable to allocate from this metaslab so determine
* a new weight for this metaslab. Now that we have loaded
* the metaslab we can provide a better hint to the metaslab
* selector.
*
* For space-based metaslabs, we use the maximum block size.
* This information is only available when the metaslab
* is loaded and is more accurate than the generic free
* space weight that was calculated by metaslab_weight().
* This information allows us to quickly compare the maximum
* available allocation in the metaslab to the allocation
* size being requested.
*
* For segment-based metaslabs, determine the new weight
* based on the highest bucket in the range tree. We
* explicitly use the loaded segment weight (i.e. the range
* tree histogram) since it contains the space that is
* currently available for allocation and is accurate
* even within a sync pass.
* a new weight for this metaslab. The weight was last
* recalculated either when we loaded it (if this is the first
* TXG it's been loaded in), or the last time a txg was synced
* out.
*/
uint64_t weight;
if (WEIGHT_IS_SPACEBASED(msp->ms_weight)) {
weight = metaslab_largest_allocatable(msp);
WEIGHT_SET_SPACEBASED(weight);
metaslab_set_fragmentation(msp, B_TRUE);
weight = metaslab_space_weight(msp) &
~METASLAB_ACTIVE_MASK;
} else {
weight = metaslab_weight_from_range_tree(msp);
}
Expand All @@ -5233,13 +5220,6 @@ metaslab_group_alloc(metaslab_group_t *mg, zio_alloc_list_t *zal,
* For the case where we use the metaslab that is
* active for another allocator we want to make
* sure that we retain the activation mask.
*
* Note that we could attempt to use something like
* metaslab_recalculate_weight_and_sort() that
* retains the activation mask here. That function
* uses metaslab_weight() to set the weight though
* which is not as accurate as the calculations
* above.
*/
weight |= msp->ms_weight & METASLAB_ACTIVE_MASK;
metaslab_group_sort(mg, msp, weight);
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