xfs: Reduce allocations during CIL insertion

Now that we have the size of the object before the formatting pass
is called, we can allocation the log vector and it's buffer in a
single allocation rather than two separate allocations.

Store the size of the allocated buffer in the log vector so that
we potentially avoid allocation for future modifications of the
object.

While touching this code, remove the IOP_FORMAT definition.
Signed-off-by: NDave Chinner <dchinner@redhat.com>
Reviewed-by: NMark Tinguely <tinguely@sgi.com>
Signed-off-by: NBen Myers <bpm@sgi.com>

fs/xfs/xfs_log.h

@@ -27,6 +27,7 @@ struct xfs_log_vec {
 	struct xfs_log_item	*lv_item;	/* owner */
 	char			*lv_buf;	/* formatted buffer */
 	int			lv_buf_len;	/* size of formatted buffer */
+	int			lv_size;	/* size of allocated lv */
 };
 
 #define XFS_LOG_VEC_ORDERED	(-1)

fs/xfs/xfs_log_cil.c

@@ -80,6 +80,36 @@ xlog_cil_init_post_recovery(
 								log->l_curr_block);
 }
 
+STATIC int
+xlog_cil_lv_item_format(
+	struct xfs_log_item	*lip,
+	struct xfs_log_vec	*lv)
+{
+	int	index;
+	char	*ptr;
+
+	/* format new vectors into array */
+	lip->li_ops->iop_format(lip, lv->lv_iovecp);
+
+	/* copy data into existing array */
+	ptr = lv->lv_buf;
+	for (index = 0; index < lv->lv_niovecs; index++) {
+		struct xfs_log_iovec *vec = &lv->lv_iovecp[index];
+
+		memcpy(ptr, vec->i_addr, vec->i_len);
+		vec->i_addr = ptr;
+		ptr += vec->i_len;
+	}
+
+	/*
+	 * some size calculations for log vectors over-estimate, so the caller
+	 * doesn't know the amount of space actually used by the item. Return
+	 * the byte count to the caller so they can check and store it
+	 * appropriately.
+	 */
+	return ptr - lv->lv_buf;
+}
+
 /*
  * Format log item into a flat buffers
  *
@@ -111,7 +141,7 @@ xlog_cil_prepare_log_vecs(
 	struct xfs_trans	*tp)
 {
 	struct xfs_log_item_desc *lidp;
-	struct xfs_log_vec	*lv = NULL;
+	struct xfs_log_vec	*prev_lv = NULL;
 	struct xfs_log_vec	*ret_lv = NULL;
 
 
@@ -123,12 +153,10 @@ xlog_cil_prepare_log_vecs(
 
 	list_for_each_entry(lidp, &tp->t_items, lid_trans) {
 		struct xfs_log_item *lip = lidp->lid_item;
-		struct xfs_log_vec *new_lv;
-		void	*ptr;
-		int	index;
-		int	len = 0;
-		uint	niovecs = 0;
-		uint	nbytes = 0;
+		struct xfs_log_vec *lv;
+		int	niovecs = 0;
+		int	nbytes = 0;
+		int	buf_size;
 		bool	ordered = false;
 
 		/* Skip items which aren't dirty in this transaction. */
@@ -150,48 +178,39 @@ xlog_cil_prepare_log_vecs(
 		if (niovecs == XFS_LOG_VEC_ORDERED) {
 			ordered = true;
 			niovecs = 0;
+			nbytes = 0;
 		}
 
-		new_lv = kmem_zalloc(sizeof(*new_lv) +
-				niovecs * sizeof(struct xfs_log_iovec),
-				KM_SLEEP|KM_NOFS);
+		/* calc buffer size */
+		buf_size = sizeof(struct xfs_log_vec) + nbytes +
+				niovecs * sizeof(struct xfs_log_iovec);
 
-		new_lv->lv_item = lip;
-		new_lv->lv_niovecs = niovecs;
+		/* allocate new data chunk */
+		lv = kmem_zalloc(buf_size, KM_SLEEP|KM_NOFS);
+		lv->lv_item = lip;
+		lv->lv_size = buf_size;
+		lv->lv_niovecs = niovecs;
 		if (ordered) {
 			/* track as an ordered logvec */
-			new_lv->lv_buf_len = XFS_LOG_VEC_ORDERED;
-			goto next;
+			ASSERT(lip->li_lv == NULL);
+			lv->lv_buf_len = XFS_LOG_VEC_ORDERED;
+			goto insert;
 		}
 
 		/* The allocated iovec region lies beyond the log vector. */
-		new_lv->lv_iovecp = (struct xfs_log_iovec *)&new_lv[1];
-
-		/* build the vector array and calculate it's length */
-		IOP_FORMAT(new_lv->lv_item, new_lv->lv_iovecp);
-		for (index = 0; index < new_lv->lv_niovecs; index++)
-			len += new_lv->lv_iovecp[index].i_len;
+		lv->lv_iovecp = (struct xfs_log_iovec *)&lv[1];
 
-		new_lv->lv_buf_len = len;
-		new_lv->lv_buf = kmem_alloc(new_lv->lv_buf_len,
-				KM_SLEEP|KM_NOFS);
-		ptr = new_lv->lv_buf;
-
-		for (index = 0; index < new_lv->lv_niovecs; index++) {
-			struct xfs_log_iovec *vec = &new_lv->lv_iovecp[index];
-
-			memcpy(ptr, vec->i_addr, vec->i_len);
-			vec->i_addr = ptr;
-			ptr += vec->i_len;
-		}
-		ASSERT(ptr == new_lv->lv_buf + new_lv->lv_buf_len);
+		/* The allocated data region lies beyond the iovec region */
+		lv->lv_buf = (char *)lv + buf_size - nbytes;
 
-next:
+		lv->lv_buf_len = xlog_cil_lv_item_format(lip, lv);
+		ASSERT(lv->lv_buf_len <= nbytes);
+insert:
 		if (!ret_lv)
-			ret_lv = new_lv;
+			ret_lv = lv;
 		else
-			lv->lv_next = new_lv;
-		lv = new_lv;
+			prev_lv->lv_next = lv;
+		prev_lv = lv;
 	}
 
 	return ret_lv;
@@ -228,7 +247,6 @@ xfs_cil_prepare_item(
 
 		*len += lv->lv_buf_len - old->lv_buf_len;
 		*diff_iovecs += lv->lv_niovecs - old->lv_niovecs;
-		kmem_free(old->lv_buf);
 		kmem_free(old);
 	} else {
 		/* new lv, must pin the log item */
@@ -354,7 +372,6 @@ xlog_cil_free_logvec(
 
 	for (lv = log_vector; lv; ) {
 		struct xfs_log_vec *next = lv->lv_next;
-		kmem_free(lv->lv_buf);
 		kmem_free(lv);
 		lv = next;
 	}

fs/xfs/xfs_trans.h

@@ -77,7 +77,6 @@ struct xfs_item_ops {
 	void (*iop_committing)(xfs_log_item_t *, xfs_lsn_t);
 };
 
-#define IOP_FORMAT(ip,vp)	(*(ip)->li_ops->iop_format)(ip, vp)
 #define IOP_PIN(ip)		(*(ip)->li_ops->iop_pin)(ip)
 #define IOP_UNPIN(ip, remove)	(*(ip)->li_ops->iop_unpin)(ip, remove)
 #define IOP_PUSH(ip, list)	(*(ip)->li_ops->iop_push)(ip, list)