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DDT: Fix several bugs in pruning

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- Fix variables types to avoid overflows after 2B entries.
 - Make ddt_prune_walk() code some more symmetrical.
 - Fix zero oldest on exact target to histogram value match.
 - Make bin 0 properly start from 0, not 1 hour.
 - Take as a cutoff base a time of histogram build start.

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Alexander Motin <[email protected]>
Closes #18838
This commit is contained in:
Alexander Motin authored and GitHub committed 2026-07-24 13:01:02 -07:00
1 parent 50557cc803
commit a04c401389
1 file changed
+18 -14
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module/zfs/ddt.c
+18 -14
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@@ -2820,8 +2820,8 @@ ddt_prune_walk(spa_t *spa, uint64_t cutoff, ddt_age_histo_t *histogram)
};
ddt_lightweight_entry_t ddlwe = {0};
int error;
int valid = 0;
int candidates = 0;
uint64_t valid = 0;
uint64_t candidates = 0;
uint64_t now = gethrestime_sec();
ddt_prune_info_t dpi;
boolean_t pruning = (cutoff != 0);
@@ -2873,8 +2873,8 @@ ddt_prune_walk(spa_t *spa, uint64_t cutoff, ddt_age_histo_t *histogram)
/* build a histogram */
if (histogram != NULL) {
uint64_t age = MAX(1, (now - class_start) / 3600);
int bin = MIN(highbit64(age) - 1, HIST_BINS - 1);
uint64_t age = (now - class_start) / 3600;
int bin = MIN(highbit64(age), HIST_BINS - 1);
histogram->dah_entries++;
histogram->dah_age_histo[bin]++;
}
@@ -2882,7 +2882,7 @@ ddt_prune_walk(spa_t *spa, uint64_t cutoff, ddt_age_histo_t *histogram)
valid++;
}
if (pruning && valid > 0) {
if (pruning) {
if (!list_is_empty(&dpi.dpi_candidates)) {
/* sync out final batch of prune candidates */
VERIFY0(dsl_sync_task(spa_name(spa), NULL,
@@ -2891,10 +2891,13 @@ ddt_prune_walk(spa_t *spa, uint64_t cutoff, ddt_age_histo_t *histogram)
}
list_destroy(&dpi.dpi_candidates);
zfs_dbgmsg("pruned %llu entries (%d%%) across %llu txg syncs",
(u_longlong_t)dpi.dpi_pruned,
(int)((dpi.dpi_pruned * 100) / valid),
(u_longlong_t)dpi.dpi_txg_syncs);
if (valid > 0) {
zfs_dbgmsg("pruned %llu entries (%llu%%) across "
"%llu txg syncs",
(u_longlong_t)dpi.dpi_pruned,
(u_longlong_t)((dpi.dpi_pruned * 100) / valid),
(u_longlong_t)dpi.dpi_txg_syncs);
}
}
}
@@ -2927,11 +2930,12 @@ ddt_prune_unique_entries(spa_t *spa, zpool_ddt_prune_unit_t unit,
if (unit == ZPOOL_DDT_PRUNE_PERCENTAGE) {
ddt_age_histo_t histogram;
uint64_t oldest = 0;
uint64_t now = gethrestime_sec();
/* Make a pass over DDT to build a histogram */
ddt_prune_walk(spa, 0, &histogram);
int target = (histogram.dah_entries * amount) / 100;
uint64_t target = (histogram.dah_entries * amount) / 100;
/*
* Figure out our cutoff date
@@ -2939,16 +2943,16 @@ ddt_prune_unique_entries(spa_t *spa, zpool_ddt_prune_unit_t unit,
*/
for (int i = HIST_BINS - 1; i >= 0 && target > 0; i--) {
if (histogram.dah_age_histo[i] != 0) {
/* less than this bucket remaining */
if (target < histogram.dah_age_histo[i]) {
oldest = MAX(1, (1<<i) * 3600);
if (target <= histogram.dah_age_histo[i]) {
oldest = (i == 0) ? 0 :
(1ULL << (i - 1)) * 3600;
target = 0;
} else {
target -= histogram.dah_age_histo[i];
}
}
}
cutoff = gethrestime_sec() - oldest;
cutoff = now - oldest;
if (ddt_dump_prune_histogram)
ddt_dump_age_histogram(&histogram, cutoff);