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Add support for POSIX_FADV_DONTNEED

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For now make it only evict the specified data from the dbuf cache.
Even though dbuf cache is small, this may still reduce eviction of
more useful data from there, and slightly accelerate ARC evictions
by making the blocks there evictable a bit sooner.

On FreeBSD this also adds support for POSIX_FADV_NOREUSE, since the
kernel translates it into POSIX_FADV_DONTNEED after every read/write.
This is not as efficient as it could be for ZFS, but that is the only
way FreeBSD kernel allows to handle POSIX_FADV_NOREUSE now.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Alexander Motin <alexander.motin@TrueNAS.com>
Closes #18399
This commit is contained in:
Alexander Motin
2026-04-07 11:56:54 -04:00
committed by Tony Hutter
parent 6f14581e1a
commit 4bb7592745
9 changed files with 169 additions and 4 deletions
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module/zfs/dbuf.c
+60
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@@ -2082,6 +2082,65 @@ dbuf_free_range(dnode_t *dn, uint64_t start_blkid, uint64_t end_blkid,
kmem_free(db_search, sizeof (dmu_buf_impl_t));
}
/*
* Advisory eviction of level-0 dbufs in [start_blkid, end_blkid] for
* the given dnode. Dirty dbufs carry a reference, so they will be
* evicted once their sync is completed.
*/
void
dbuf_evict_range(dnode_t *dn, uint64_t start_blkid, uint64_t end_blkid)
{
dmu_buf_impl_t *db_marker;
dmu_buf_impl_t *db, *db_next;
avl_index_t where;
db_marker = kmem_alloc(sizeof (dmu_buf_impl_t), KM_SLEEP);
db_marker->db_level = 0;
db_marker->db_blkid = start_blkid;
db_marker->db_state = DB_SEARCH;
mutex_enter(&dn->dn_dbufs_mtx);
db = avl_find(&dn->dn_dbufs, db_marker, &where);
ASSERT0P(db);
db = avl_nearest(&dn->dn_dbufs, where, AVL_AFTER);
for (; db != NULL; db = db_next) {
if (db->db_level != 0 || db->db_blkid > end_blkid)
break;
mutex_enter(&db->db_mtx);
if (db->db_state != DB_EVICTING &&
zfs_refcount_is_zero(&db->db_holds)) {
/*
* Clean and unreferenced: evict immediately.
* Use the marker pattern from dnode_evict_dbufs()
* because dbuf_destroy() may recursively remove
* the parent indirect dbuf from dn_dbufs, which
* could be the node db_next would point to.
*/
db_marker->db_level = db->db_level;
db_marker->db_blkid = db->db_blkid;
db_marker->db_state = DB_MARKER;
db_marker->db_parent =
(void *)((uintptr_t)db - 1);
avl_insert_here(&dn->dn_dbufs, db_marker,
db, AVL_BEFORE);
dbuf_destroy(db);
db_next = AVL_NEXT(&dn->dn_dbufs, db_marker);
avl_remove(&dn->dn_dbufs, db_marker);
} else {
/* Referenced (possibly dirty): evict when released. */
db->db_pending_evict = TRUE;
db->db_partial_read = FALSE;
mutex_exit(&db->db_mtx);
db_next = AVL_NEXT(&dn->dn_dbufs, db);
}
}
mutex_exit(&dn->dn_dbufs_mtx);
kmem_free(db_marker, sizeof (dmu_buf_impl_t));
}
void
dbuf_new_size(dmu_buf_impl_t *db, int size, dmu_tx_t *tx)
{
@@ -5462,6 +5521,7 @@ EXPORT_SYMBOL(dbuf_whichblock);
EXPORT_SYMBOL(dbuf_read);
EXPORT_SYMBOL(dbuf_unoverride);
EXPORT_SYMBOL(dbuf_free_range);
EXPORT_SYMBOL(dbuf_evict_range);
EXPORT_SYMBOL(dbuf_new_size);
EXPORT_SYMBOL(dbuf_release_bp);
EXPORT_SYMBOL(dbuf_dirty);