Gang ABD Type

Adding the Gang ABD type, which allows for linear and scatter ABDs to be chained together into a single ABD. This can be used to avoid doing memory copies to/from ABDs. An example of this can be found in vdev_queue.c in the vdev_queue_aggregate() function. Signed-off-by: Brian Atkinson <[email protected]> Co-authored-by: Mark Maybee <[email protected]> Co-authored-by: Brian Atkinson <[email protected]>
openzfs · May 5, 2020 · 610988c · 610988c
1 parent 28f8cad
commit 610988c
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Showing 7 changed files with 626 additions and 102 deletions.
diff --git a/include/sys/abd.h b/include/sys/abd.h
@@ -42,20 +42,24 @@ typedef int abd_iter_func_t(void *buf, size_t len, void *private);
 typedef int abd_iter_func2_t(void *bufa, void *bufb, size_t len, void *private);
 
 extern int zfs_abd_scatter_enabled;
+extern abd_t *abd_zero_scatter;
 
 /*
  * Allocations and deallocations
  */
 
 abd_t *abd_alloc(size_t, boolean_t);
 abd_t *abd_alloc_linear(size_t, boolean_t);
+abd_t *abd_alloc_gang_abd(void);
 abd_t *abd_alloc_for_io(size_t, boolean_t);
 abd_t *abd_alloc_sametype(abd_t *, size_t);
+void abd_gang_add(abd_t *, abd_t *, boolean_t);
 void abd_free(abd_t *);
+void abd_put(abd_t *);
 abd_t *abd_get_offset(abd_t *, size_t);
 abd_t *abd_get_offset_size(abd_t *, size_t, size_t);
+abd_t *abd_get_zeros(size_t);
 abd_t *abd_get_from_buf(void *, size_t);
-void abd_put(abd_t *);
 
 /*
  * Conversion to and from a normal buffer
@@ -132,6 +136,7 @@ abd_zero(abd_t *abd, size_t size)
  * ABD type check functions
  */
 boolean_t abd_is_linear(abd_t *);
+boolean_t abd_is_gang_abd(abd_t *);
 boolean_t abd_is_linear_page(abd_t *);
 
 /*
@@ -146,8 +151,7 @@ void abd_fini(void);
  * Linux ABD bio functions
  */
 #if defined(__linux__) && defined(_KERNEL)
-unsigned int abd_scatter_bio_map_off(struct bio *, abd_t *, unsigned int,
-    size_t);
+unsigned int abd_bio_map_off(struct bio *, abd_t *, unsigned int, size_t);
 unsigned long abd_nr_pages_off(abd_t *, unsigned int, size_t);
 #endif
 

diff --git a/include/sys/abd_impl.h b/include/sys/abd_impl.h
@@ -39,6 +39,9 @@ typedef enum abd_flags {
 	ABD_FLAG_MULTI_ZONE  	= 1 << 3, /* pages split over memory zones */
 	ABD_FLAG_MULTI_CHUNK 	= 1 << 4, /* pages split over multiple chunks */
 	ABD_FLAG_LINEAR_PAGE 	= 1 << 5, /* linear but allocd from page */
+	ABD_FLAG_GANG		= 1 << 6, /* mult ABDs chained together */
+	ABD_FLAG_GANG_FREE	= 1 << 7, /* gang ABD is responsible for mem */
+	ABD_FLAG_ZEROS		= 1 << 8, /* ABD for zero-filled buffer */
 } abd_flags_t;
 
 typedef enum abd_stats_op {
@@ -49,8 +52,10 @@ typedef enum abd_stats_op {
 struct abd {
 	abd_flags_t	abd_flags;
 	uint_t		abd_size;	/* excludes scattered abd_offset */
+	list_node_t	abd_gang_link;
 	struct abd	*abd_parent;
 	zfs_refcount_t	abd_children;
+	kmutex_t	abd_mtx;
 	union {
 		struct abd_scatter {
 			uint_t		abd_offset;
@@ -66,6 +71,9 @@ struct abd {
 			void		*abd_buf;
 			struct scatterlist *abd_sgl; /* for LINEAR_PAGE */
 		} abd_linear;
+		struct abd_gang {
+			list_t abd_gang_chain;
+		} abd_gang;
 	} abd_u;
 };
 
@@ -84,6 +92,14 @@ struct abd_iter {
 	struct scatterlist *iter_sg;	/* current sg */
 };
 
+/*
+ * This is used to get an ABD from an Gang ABD's list based on
+ * the provided offset. This should only be called from the
+ * ABD source code.
+ */
+abd_t *abd_gang_get_offset(abd_t *, size_t *);
+
+
 /*
  * OS specific functions
  */
@@ -119,7 +135,7 @@ void abd_iter_unmap(struct abd_iter *);
 
 #define	ABD_SCATTER(abd)	(abd->abd_u.abd_scatter)
 #define	ABD_LINEAR_BUF(abd)	(abd->abd_u.abd_linear.abd_buf)
-#define	ABD_MULTI(abd)		(abd->abd_u.abd_multi)
+#define	ABD_GANG(abd)		(abd->abd_u.abd_gang)
 
 #ifdef __cplusplus
 }

diff --git a/module/os/freebsd/zfs/abd_os.c b/module/os/freebsd/zfs/abd_os.c
@@ -130,6 +130,17 @@ SYSCTL_ULONG(_vfs_zfs, OID_AUTO, abd_chunk_size, CTLFLAG_RDTUN,
 kmem_cache_t *abd_chunk_cache;
 static kstat_t *abd_ksp;
 
+/*
+ * We use a scattered SPA_MAXBLOCKSIZE sized ABD whose chunks are
+ * just a single zero'd sized zfs_abd_chunk_size buffer. This
+ * allows us to conserve memory by only using a single zero buffer
+ * for the scatter chunks.
+ */
+abd_t *abd_zero_scatter = NULL;
+static char *abd_zero_buf = NULL;
+
+#define	ABD_ZERO_PAGE (abd_zero_buf)
+
 static void
 abd_free_chunk(void *c)
 {
@@ -228,6 +239,8 @@ abd_alloc_struct(size_t chunkcnt)
 	    abd_u.abd_scatter.abd_chunks[chunkcnt]);
 	abd_t *abd = kmem_alloc(abd_size, KM_PUSHPAGE);
 	ASSERT3P(abd, !=, NULL);
+	list_link_init(&abd->abd_gang_link);
+	mutex_init(&abd->abd_mtx, NULL, MUTEX_DEFAULT, NULL);
 	ABDSTAT_INCR(abdstat_struct_size, abd_size);
 
 	return (abd);
@@ -238,10 +251,54 @@ abd_free_struct(abd_t *abd)
 {
 	size_t chunkcnt = abd_is_linear(abd) ? 0 : abd_scatter_chunkcnt(abd);
 	int size = offsetof(abd_t, abd_u.abd_scatter.abd_chunks[chunkcnt]);
+	mutex_destroy(&abd->abd_mtx);
+	ASSERT(!list_link_active(&abd->abd_gang_link));
 	kmem_free(abd, size);
 	ABDSTAT_INCR(abdstat_struct_size, -size);
 }
 
+/*
+ * Allocate scatter ABD of size SPA_MAXBLOCKSIZE, where
+ * each page in the scatterlist will be set to ABD_ZERO_PAGE.
+ */
+static void
+abd_alloc_zero_scatter(void)
+{
+	size_t n = abd_chunkcnt_for_bytes(SPA_MAXBLOCKSIZE);
+	abd_zero_buf = kmem_zalloc(zfs_abd_chunk_size, KM_SLEEP);
+	abd_zero_scatter = abd_alloc_struct(n);
+
+	abd_zero_scatter->abd_flags = ABD_FLAG_OWNER;
+	abd_zero_scatter->abd_flags |= ABD_FLAG_ZEROS;
+	abd_zero_scatter->abd_size = SPA_MAXBLOCKSIZE;
+	abd_zero_scatter->abd_parent = NULL;
+	zfs_refcount_create(&abd_zero_scatter->abd_children);
+
+	ABD_SCATTER(abd_zero_scatter).abd_offset = 0;
+	ABD_SCATTER(abd_zero_scatter).abd_chunk_size =
+	    zfs_abd_chunk_size;
+
+	for (int i = 0; i < n; i++) {
+		ABD_SCATTER(abd_zero_scatter).abd_chunks[i] =
+		    ABD_ZERO_PAGE;
+	}
+
+	ABDSTAT_BUMP(abdstat_scatter_cnt);
+	ABDSTAT_INCR(abdstat_scatter_data_size, zfs_abd_chunk_size);
+}
+
+static void
+abd_free_zero_scatter(void)
+{
+	zfs_refcount_destroy(&abd_zero_scatter->abd_children);
+	ABDSTAT_BUMPDOWN(abdstat_scatter_cnt);
+	ABDSTAT_INCR(abdstat_scatter_data_size, -(int)zfs_abd_chunk_size);
+
+	abd_free_struct(abd_zero_scatter);
+	abd_zero_scatter = NULL;
+	kmem_free(abd_zero_buf, zfs_abd_chunk_size);
+}
+
 void
 abd_init(void)
 {
@@ -254,11 +311,15 @@ abd_init(void)
 		abd_ksp->ks_data = &abd_stats;
 		kstat_install(abd_ksp);
 	}
+
+	abd_alloc_zero_scatter();
 }
 
 void
 abd_fini(void)
 {
+	abd_free_zero_scatter();
+
 	if (abd_ksp != NULL) {
 		kstat_delete(abd_ksp);
 		abd_ksp = NULL;
@@ -363,6 +424,7 @@ abd_iter_scatter_chunk_index(struct abd_iter *aiter)
 void
 abd_iter_init(struct abd_iter *aiter, abd_t *abd)
 {
+	ASSERT(!abd_is_gang_abd(abd));
 	abd_verify(abd);
 	aiter->iter_abd = abd;
 	aiter->iter_pos = 0;