Add visibility in to cached dbufs

Currently there is no mechanism to inspect which dbufs are being
cached by the system.  There are some coarse counters in arcstats
by they only give a rough idea of what's being cached.  This patch
aims to improve the current situation by adding a new dbufs kstat.

When read this new kstat will walk all cached dbufs linked in to
the dbuf_hash.  For each dbuf it will dump detailed information
about the buffer.  It will also dump additional information about
the referenced arc buffer and its related dnode.  This provides a
more complete view in to exactly what is being cached.

With this generic infrastructure in place utilities can be written
to post-process the data to understand exactly how the caching is
working.  For example, the data could be processed to show a list
of all cached dnodes and how much space they're consuming.  Or a
similar list could be generated based on dnode type.  Many other
ways to interpret the data exist based on what kinds of questions
you're trying to answer.

Signed-off-by: Brian Behlendorf <[email protected]>
Signed-off-by: Prakash Surya <[email protected]>

1 files changed, 31 insertions, 0 deletions

diff --git a/include/sys/arc.h b/include/sys/arc.h
index 8c10d947c..efafb551a 100644
--- a/include/sys/arc.h
+++ b/include/sys/arc.h
@@ -92,6 +92,36 @@ typedef enum arc_space_type {
 	ARC_SPACE_NUMTYPES
 } arc_space_type_t;
 
+typedef enum arc_state_type {
+	ARC_STATE_ANON,
+	ARC_STATE_MRU,
+	ARC_STATE_MRU_GHOST,
+	ARC_STATE_MFU,
+	ARC_STATE_MFU_GHOST,
+	ARC_STATE_L2C_ONLY,
+	ARC_STATE_NUMTYPES
+} arc_state_type_t;
+
+typedef struct arc_buf_info {
+	arc_state_type_t	abi_state_type;
+	arc_buf_contents_t	abi_state_contents;
+	uint64_t		abi_state_index;
+	uint32_t		abi_flags;
+	uint32_t		abi_datacnt;
+	uint64_t		abi_size;
+	uint64_t		abi_spa;
+	uint64_t		abi_access;
+	uint32_t		abi_mru_hits;
+	uint32_t		abi_mru_ghost_hits;
+	uint32_t		abi_mfu_hits;
+	uint32_t		abi_mfu_ghost_hits;
+	uint32_t		abi_l2arc_hits;
+	uint32_t		abi_holds;
+	uint64_t		abi_l2arc_dattr;
+	uint64_t		abi_l2arc_asize;
+	enum zio_compress	abi_l2arc_compress;
+} arc_buf_info_t;
+
 void arc_space_consume(uint64_t space, arc_space_type_t type);
 void arc_space_return(uint64_t space, arc_space_type_t type);
 arc_buf_t *arc_buf_alloc(spa_t *spa, int size, void *tag,
@@ -101,6 +131,7 @@ void arc_return_buf(arc_buf_t *buf, void *tag);
 void arc_loan_inuse_buf(arc_buf_t *buf, void *tag);
 void arc_buf_add_ref(arc_buf_t *buf, void *tag);
 boolean_t arc_buf_remove_ref(arc_buf_t *buf, void *tag);
+void arc_buf_info(arc_buf_t *buf, arc_buf_info_t *abi, int state_index);
 int arc_buf_size(arc_buf_t *buf);
 void arc_release(arc_buf_t *buf, void *tag);
 int arc_released(arc_buf_t *buf);