*/
typedef struct arc_state {
- list_t arcs_list[ARC_BUFC_NUMTYPES]; /* list of evictable buffers */
- uint64_t arcs_lsize[ARC_BUFC_NUMTYPES]; /* amount of evictable data */
- uint64_t arcs_size; /* total amount of data in this state */
- kmutex_t arcs_mtx;
+ /*
+ * list of evictable buffers
+ */
+ multilist_t arcs_list[ARC_BUFC_NUMTYPES];
+ /*
+ * total amount of evictable data in this state
+ */
+ uint64_t arcs_lsize[ARC_BUFC_NUMTYPES];
+ /*
+ * total amount of data in this state; this includes: evictable,
+ * non-evictable, ARC_BUFC_DATA, and ARC_BUFC_METADATA.
+ */
+ refcount_t arcs_size;
+ /*
+ * supports the "dbufs" kstat
+ */
arc_state_type_t arcs_state;
} arc_state_t;
-typedef struct l2arc_buf_hdr l2arc_buf_hdr_t;
-
typedef struct arc_callback arc_callback_t;
struct arc_callback {
arc_buf_t *awcb_buf;
};
-struct arc_buf_hdr {
- /* protected by hash lock */
- dva_t b_dva;
- uint64_t b_birth;
- uint64_t b_cksum0;
-
+/*
+ * ARC buffers are separated into multiple structs as a memory saving measure:
+ * - Common fields struct, always defined, and embedded within it:
+ * - L2-only fields, always allocated but undefined when not in L2ARC
+ * - L1-only fields, only allocated when in L1ARC
+ *
+ * Buffer in L1 Buffer only in L2
+ * +------------------------+ +------------------------+
+ * | arc_buf_hdr_t | | arc_buf_hdr_t |
+ * | | | |
+ * | | | |
+ * | | | |
+ * +------------------------+ +------------------------+
+ * | l2arc_buf_hdr_t | | l2arc_buf_hdr_t |
+ * | (undefined if L1-only) | | |
+ * +------------------------+ +------------------------+
+ * | l1arc_buf_hdr_t |
+ * | |
+ * | |
+ * | |
+ * | |
+ * +------------------------+
+ *
+ * Because it's possible for the L2ARC to become extremely large, we can wind
+ * up eating a lot of memory in L2ARC buffer headers, so the size of a header
+ * is minimized by only allocating the fields necessary for an L1-cached buffer
+ * when a header is actually in the L1 cache. The sub-headers (l1arc_buf_hdr and
+ * l2arc_buf_hdr) are embedded rather than allocated separately to save a couple
+ * words in pointers. arc_hdr_realloc() is used to switch a header between
+ * these two allocation states.
+ */
+typedef struct l1arc_buf_hdr {
kmutex_t b_freeze_lock;
- zio_cksum_t *b_freeze_cksum;
- arc_buf_hdr_t *b_hash_next;
arc_buf_t *b_buf;
- uint32_t b_flags;
uint32_t b_datacnt;
-
- arc_callback_t *b_acb;
+ /* for waiting on writes to complete */
kcondvar_t b_cv;
- /* immutable */
- arc_buf_contents_t b_type;
- uint64_t b_size;
- uint64_t b_spa;
/* protected by arc state mutex */
arc_state_t *b_state;
- list_node_t b_arc_node;
+ multilist_node_t b_arc_node;
/* updated atomically */
clock_t b_arc_access;
/* self protecting */
refcount_t b_refcnt;
- l2arc_buf_hdr_t *b_l2hdr;
- list_node_t b_l2node;
-};
+ arc_callback_t *b_acb;
+ /* temporary buffer holder for in-flight compressed data */
+ void *b_tmp_cdata;
+} l1arc_buf_hdr_t;
typedef struct l2arc_dev {
vdev_t *l2ad_vdev; /* vdev */
uint64_t l2ad_hand; /* next write location */
uint64_t l2ad_start; /* first addr on device */
uint64_t l2ad_end; /* last addr on device */
- uint64_t l2ad_evict; /* last addr eviction reached */
boolean_t l2ad_first; /* first sweep through */
boolean_t l2ad_writing; /* currently writing */
- list_t *l2ad_buflist; /* buffer list */
+ kmutex_t l2ad_mtx; /* lock for buffer list */
+ list_t l2ad_buflist; /* buffer list */
list_node_t l2ad_node; /* device list node */
+ refcount_t l2ad_alloc; /* allocated bytes */
} l2arc_dev_t;
+typedef struct l2arc_buf_hdr {
+ /* protected by arc_buf_hdr mutex */
+ l2arc_dev_t *b_dev; /* L2ARC device */
+ uint64_t b_daddr; /* disk address, offset byte */
+ /* real alloc'd buffer size depending on b_compress applied */
+ uint32_t b_hits;
+ int32_t b_asize;
+ uint8_t b_compress;
+
+ list_node_t b_l2node;
+} l2arc_buf_hdr_t;
+
typedef struct l2arc_write_callback {
l2arc_dev_t *l2wcb_dev; /* device info */
arc_buf_hdr_t *l2wcb_head; /* head of write buflist */
} l2arc_write_callback_t;
+struct arc_buf_hdr {
+ /* protected by hash lock */
+ dva_t b_dva;
+ uint64_t b_birth;
+ /*
+ * Even though this checksum is only set/verified when a buffer is in
+ * the L1 cache, it needs to be in the set of common fields because it
+ * must be preserved from the time before a buffer is written out to
+ * L2ARC until after it is read back in.
+ */
+ zio_cksum_t *b_freeze_cksum;
+
+ arc_buf_hdr_t *b_hash_next;
+ arc_flags_t b_flags;
+
+ /* immutable */
+ int32_t b_size;
+ uint64_t b_spa;
+
+ /* L2ARC fields. Undefined when not in L2ARC. */
+ l2arc_buf_hdr_t b_l2hdr;
+ /* L1ARC fields. Undefined when in l2arc_only state */
+ l1arc_buf_hdr_t b_l1hdr;
+};
#ifdef __cplusplus
}
#endif
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