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BRT: Implement partial bv_entcount writing

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From the introduction of BRT the bv_entcount was always written all
at once, even though there was a mechanism for partial writing.
Implement one finally to slightly reduce per-TXG dirty data and write
inflation on large pools.  On 1PB pool it meant 128MB write for each
TXG modifying BRT.

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Alexander Motin <[email protected]>
Closes #18821
This commit is contained in:
Alexander Motin authored and GitHub committed 2026-07-22 09:47:43 -07:00
1 parent bd2d87399c
commit 87e2e40475
1 file changed
+16 -10
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module/zfs/brt.c
+16 -10
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@@ -759,8 +759,7 @@ brt_vdev_addref(spa_t *spa, brt_vdev_t *brtvd, const brt_entry_t *bre,
brtvd->bv_totalcount++;
brt_vdev_entcount_inc(brtvd, idx);
brtvd->bv_entcount_dirty = TRUE;
idx = idx / BRT_BLOCKSIZE / 8;
BT_SET(brtvd->bv_bitmap, idx);
BT_SET(brtvd->bv_bitmap, idx / (BRT_BLOCKSIZE / sizeof (uint16_t)));
}
static void
@@ -787,8 +786,7 @@ brt_vdev_decref(spa_t *spa, brt_vdev_t *brtvd, const brt_entry_t *bre,
brtvd->bv_totalcount--;
brt_vdev_entcount_dec(brtvd, idx);
brtvd->bv_entcount_dirty = TRUE;
idx = idx / BRT_BLOCKSIZE / 8;
BT_SET(brtvd->bv_bitmap, idx);
BT_SET(brtvd->bv_bitmap, idx / (BRT_BLOCKSIZE / sizeof (uint16_t)));
}
static void
@@ -805,13 +803,21 @@ brt_vdev_sync(spa_t *spa, brt_vdev_t *brtvd, dmu_tx_t *tx)
FTAG, &db));
if (brtvd->bv_entcount_dirty) {
/*
* TODO: Walk brtvd->bv_bitmap and write only the dirty blocks.
*/
uint64_t nblocks = BRT_RANGESIZE_TO_NBLOCKS(brtvd->bv_size);
dmu_write(spa->spa_meta_objset, brtvd->bv_mos_brtvdev, 0,
nblocks * BRT_BLOCKSIZE, brtvd->bv_entcount, tx,
DMU_READ_NO_PREFETCH | DMU_UNCACHEDIO);
for (uint64_t i = 0; i < nblocks; i++) {
if (!BT_TEST(brtvd->bv_bitmap, i))
continue;
uint64_t end = i + 1;
uint64_t maxend = MIN(i + DMU_MAX_ACCESS / 2 /
BRT_BLOCKSIZE, nblocks);
while (end < maxend && BT_TEST(brtvd->bv_bitmap, end))
end++;
dmu_write(spa->spa_meta_objset, brtvd->bv_mos_brtvdev,
i * BRT_BLOCKSIZE, (end - i) * BRT_BLOCKSIZE,
(char *)brtvd->bv_entcount + i * BRT_BLOCKSIZE,
tx, DMU_READ_NO_PREFETCH | DMU_UNCACHEDIO);
i = end - 1;
}
memset(brtvd->bv_bitmap, 0, BT_SIZEOFMAP(nblocks));
brtvd->bv_entcount_dirty = FALSE;
}