Exclude special allocation class buffers from L2ARC

Special allocation class vdevs may have roughly the same performance as L2ARC vdevs. Exclude those buffers from being cacheable on L2ARC. Signed-off-by: George Amanakis <gamanakis@gmail.com>
openzfs · Jun 28, 2021 · 427da3d · 427da3d
1 parent f20fb19
commit 427da3d
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Showing 3 changed files with 34 additions and 7 deletions.
diff --git a/include/sys/dbuf.h b/include/sys/dbuf.h
@@ -37,6 +37,9 @@
 #include <sys/zfs_refcount.h>
 #include <sys/zrlock.h>
 #include <sys/multilist.h>
+#include <sys/vdev_impl.h>
+#include <sys/spa_impl.h>
+#include <sys/dmu_objset.h>
 
 #ifdef	__cplusplus
 extern "C" {
@@ -442,10 +445,34 @@ dbuf_find_dirty_eq(dmu_buf_impl_t *db, uint64_t txg)
 	(dbuf_is_metadata(_db) &&					\
 	((_db)->db_objset->os_primary_cache == ZFS_CACHE_METADATA)))
 
-#define	DBUF_IS_L2CACHEABLE(_db)					\
-	((_db)->db_objset->os_secondary_cache == ZFS_CACHE_ALL ||	\
-	(dbuf_is_metadata(_db) &&					\
-	((_db)->db_objset->os_secondary_cache == ZFS_CACHE_METADATA)))
+/*
+ * We want to exclude buffers that are on a special allocation class from
+ * L2ARC.
+ */
+static inline boolean_t dbuf_is_l2cacheable(dmu_buf_impl_t *db)
+{
+	blkptr_t *bp = db->db_blkptr;
+	spa_t *spa = db->db_objset->os_spa;
+	uint64_t vdev = DVA_GET_VDEV(db->db_blkptr->blk_dva);
+	vdev_t *vd = NULL;
+
+	if (bp != NULL) {
+		vdev_t *rvd = spa->spa_root_vdev;
+
+		if (vdev < rvd->vdev_children) {
+			ASSERT(rvd->vdev_child[vdev] != NULL);
+			vd = rvd->vdev_child[vdev];
+		}
+	}
+
+	if ((db->db_objset->os_secondary_cache == ZFS_CACHE_ALL ||
+	    (dbuf_is_metadata(db) &&
+	    db->db_objset->os_secondary_cache == ZFS_CACHE_METADATA)) &&
+	    !(vd != NULL && vd->vdev_alloc_bias == VDEV_BIAS_SPECIAL))
+		return (B_TRUE);
+
+	return (B_FALSE);
+}
 
 #define	DNODE_LEVEL_IS_L2CACHEABLE(_dn, _level)				\
 	((_dn)->dn_objset->os_secondary_cache == ZFS_CACHE_ALL ||	\

diff --git a/module/zfs/dbuf.c b/module/zfs/dbuf.c
@@ -1526,7 +1526,7 @@ dbuf_read_impl(dmu_buf_impl_t *db, zio_t *zio, uint32_t flags,
 	DTRACE_SET_STATE(db, "read issued");
 	mutex_exit(&db->db_mtx);
 
-	if (DBUF_IS_L2CACHEABLE(db))
+	if (dbuf_is_l2cacheable(db))
 		aflags |= ARC_FLAG_L2CACHE;
 
 	dbuf_add_ref(db, NULL);
@@ -4985,7 +4985,7 @@ dbuf_write(dbuf_dirty_record_t *dr, arc_buf_t *data, dmu_tx_t *tx)
 			children_ready_cb = dbuf_write_children_ready;
 
 		dr->dr_zio = arc_write(pio, os->os_spa, txg,
-		    &dr->dr_bp_copy, data, DBUF_IS_L2CACHEABLE(db),
+		    &dr->dr_bp_copy, data, dbuf_is_l2cacheable(db),
 		    &zp, dbuf_write_ready,
 		    children_ready_cb, dbuf_write_physdone,
 		    dbuf_write_done, db, ZIO_PRIORITY_ASYNC_WRITE,

diff --git a/module/zfs/dmu.c b/module/zfs/dmu.c
@@ -1841,7 +1841,7 @@ dmu_sync(zio_t *pio, uint64_t txg, dmu_sync_cb_t *done, zgd_t *zgd)
 	dsa->dsa_tx = NULL;
 
 	zio_nowait(arc_write(pio, os->os_spa, txg,
-	    zgd->zgd_bp, dr->dt.dl.dr_data, DBUF_IS_L2CACHEABLE(db),
+	    zgd->zgd_bp, dr->dt.dl.dr_data, dbuf_is_l2cacheable(db),
 	    &zp, dmu_sync_ready, NULL, NULL, dmu_sync_done, dsa,
 	    ZIO_PRIORITY_SYNC_WRITE, ZIO_FLAG_CANFAIL, &zb));