ocfs2: allocation hints

Record the most recently used allocation group on the allocation context, so
that subsequent allocations can attempt to optimize for contiguousness.
Local alloc especially should benefit from this as the current chain search
tends to let it spew across the disk.
Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>

fs/ocfs2/localalloc.c

@@ -840,6 +840,12 @@ static int ocfs2_local_alloc_new_window(struct ocfs2_super *osb,
 
 	mlog(0, "Allocating %u clusters for a new window.\n",
 	     ocfs2_local_alloc_window_bits(osb));
+
+	/* Instruct the allocation code to try the most recently used
+	 * cluster group. We'll re-record the group used this pass
+	 * below. */
+	ac->ac_last_group = osb->la_last_gd;
+
 	/* we used the generic suballoc reserve function, but we set
 	 * everything up nicely, so there's no reason why we can't use
 	 * the more specific cluster api to claim bits. */
@@ -852,6 +858,8 @@ static int ocfs2_local_alloc_new_window(struct ocfs2_super *osb,
 		goto bail;
 	}
 
+	osb->la_last_gd = ac->ac_last_group;
+
 	la->la_bm_off = cpu_to_le32(cluster_off);
 	alloc->id1.bitmap1.i_total = cpu_to_le32(cluster_count);
 	/* just in case... In the future when we find space ourselves,

fs/ocfs2/ocfs2.h

@@ -236,6 +236,7 @@ struct ocfs2_super
 
 	enum ocfs2_local_alloc_state local_alloc_state;
 	struct buffer_head *local_alloc_bh;
+	u64 la_last_gd;
 
 	/* Next two fields are for local node slot recovery during
 	 * mount. */

fs/ocfs2/suballoc.c

@@ -70,12 +70,6 @@ static int ocfs2_block_group_search(struct inode *inode,
 				    struct buffer_head *group_bh,
 				    u32 bits_wanted, u32 min_bits,
 				    u16 *bit_off, u16 *bits_found);
-static int ocfs2_search_chain(struct ocfs2_alloc_context *ac,
-			      u32 bits_wanted,
-			      u32 min_bits,
-			      u16 *bit_off,
-			      unsigned int *num_bits,
-			      u64 *bg_blkno);
 static int ocfs2_claim_suballoc_bits(struct ocfs2_super *osb,
 				     struct ocfs2_alloc_context *ac,
 				     u32 bits_wanted,
@@ -1030,12 +1024,103 @@ static int ocfs2_block_group_search(struct inode *inode,
 	return ret;
 }
 
+static int ocfs2_alloc_dinode_update_counts(struct inode *inode,
+				       struct ocfs2_journal_handle *handle,
+				       struct buffer_head *di_bh,
+				       u32 num_bits,
+				       u16 chain)
+{
+	int ret;
+	u32 tmp_used;
+	struct ocfs2_dinode *di = (struct ocfs2_dinode *) di_bh->b_data;
+	struct ocfs2_chain_list *cl = (struct ocfs2_chain_list *) &di->id2.i_chain;
+
+	ret = ocfs2_journal_access(handle, inode, di_bh,
+				   OCFS2_JOURNAL_ACCESS_WRITE);
+	if (ret < 0) {
+		mlog_errno(ret);
+		goto out;
+	}
+
+	tmp_used = le32_to_cpu(di->id1.bitmap1.i_used);
+	di->id1.bitmap1.i_used = cpu_to_le32(num_bits + tmp_used);
+	le32_add_cpu(&cl->cl_recs[chain].c_free, -num_bits);
+
+	ret = ocfs2_journal_dirty(handle, di_bh);
+	if (ret < 0)
+		mlog_errno(ret);
+
+out:
+	return ret;
+}
+
+static int ocfs2_search_one_group(struct ocfs2_alloc_context *ac,
+				  u32 bits_wanted,
+				  u32 min_bits,
+				  u16 *bit_off,
+				  unsigned int *num_bits,
+				  u64 gd_blkno,
+				  u16 *bits_left)
+{
+	int ret;
+	u16 found;
+	struct buffer_head *group_bh = NULL;
+	struct ocfs2_group_desc *gd;
+	struct inode *alloc_inode = ac->ac_inode;
+	struct ocfs2_journal_handle *handle = ac->ac_handle;
+
+	ret = ocfs2_read_block(OCFS2_SB(alloc_inode->i_sb), gd_blkno,
+			       &group_bh, OCFS2_BH_CACHED, alloc_inode);
+	if (ret < 0) {
+		mlog_errno(ret);
+		return ret;
+	}
+
+	gd = (struct ocfs2_group_desc *) group_bh->b_data;
+	if (!OCFS2_IS_VALID_GROUP_DESC(gd)) {
+		OCFS2_RO_ON_INVALID_GROUP_DESC(alloc_inode->i_sb, gd);
+		ret = -EIO;
+		goto out;
+	}
+
+	ret = ac->ac_group_search(alloc_inode, group_bh, bits_wanted, min_bits,
+				  bit_off, &found);
+	if (ret < 0) {
+		if (ret != -ENOSPC)
+			mlog_errno(ret);
+		goto out;
+	}
+
+	*num_bits = found;
+
+	ret = ocfs2_alloc_dinode_update_counts(alloc_inode, handle, ac->ac_bh,
+					       *num_bits,
+					       le16_to_cpu(gd->bg_chain));
+	if (ret < 0) {
+		mlog_errno(ret);
+		goto out;
+	}
+
+	ret = ocfs2_block_group_set_bits(handle, alloc_inode, gd, group_bh,
+					 *bit_off, *num_bits);
+	if (ret < 0)
+		mlog_errno(ret);
+
+	*bits_left = le16_to_cpu(gd->bg_free_bits_count);
+
+out:
+	brelse(group_bh);
+
+	return ret;
+}
+
 static int ocfs2_search_chain(struct ocfs2_alloc_context *ac,
 			      u32 bits_wanted,
 			      u32 min_bits,
 			      u16 *bit_off,
 			      unsigned int *num_bits,
-			      u64 *bg_blkno)
+			      u64 *bg_blkno,
+			      u16 *bits_left)
 {
 	int status;
 	u16 chain, tmp_bits;
@@ -1173,6 +1258,7 @@ static int ocfs2_search_chain(struct ocfs2_alloc_context *ac,
 	     (unsigned long long)fe->i_blkno);
 
 	*bg_blkno = le64_to_cpu(bg->bg_blkno);
+	*bits_left = le16_to_cpu(bg->bg_free_bits_count);
 bail:
 	if (group_bh)
 		brelse(group_bh);
@@ -1194,6 +1280,8 @@ static int ocfs2_claim_suballoc_bits(struct ocfs2_super *osb,
 {
 	int status;
 	u16 victim, i;
+	u16 bits_left = 0;
+	u64 hint_blkno = ac->ac_last_group;
 	struct ocfs2_chain_list *cl;
 	struct ocfs2_dinode *fe;
 
@@ -1220,6 +1308,28 @@ static int ocfs2_claim_suballoc_bits(struct ocfs2_super *osb,
 		goto bail;
 	}
 
+	if (hint_blkno) {
+		/* Attempt to short-circuit the usual search mechanism
+		 * by jumping straight to the most recently used
+		 * allocation group. This helps us mantain some
+		 * contiguousness across allocations. */
+		status = ocfs2_search_one_group(ac, bits_wanted, min_bits,
+						bit_off, num_bits,
+						hint_blkno, &bits_left);
+		if (!status) {
+			/* Be careful to update *bg_blkno here as the
+			 * caller is expecting it to be filled in, and
+			 * ocfs2_search_one_group() won't do that for
+			 * us. */
+			*bg_blkno = hint_blkno;
+			goto set_hint;
+		}
+		if (status < 0 && status != -ENOSPC) {
+			mlog_errno(status);
+			goto bail;
+		}
+	}
+
 	cl = (struct ocfs2_chain_list *) &fe->id2.i_chain;
 
 	victim = ocfs2_find_victim_chain(cl);
@@ -1227,9 +1337,9 @@ static int ocfs2_claim_suballoc_bits(struct ocfs2_super *osb,
 	ac->ac_allow_chain_relink = 1;
 
 	status = ocfs2_search_chain(ac, bits_wanted, min_bits, bit_off,
-				    num_bits, bg_blkno);
+				    num_bits, bg_blkno, &bits_left);
 	if (!status)
-		goto bail;
+		goto set_hint;
 	if (status < 0 && status != -ENOSPC) {
 		mlog_errno(status);
 		goto bail;
@@ -1251,8 +1361,8 @@ static int ocfs2_claim_suballoc_bits(struct ocfs2_super *osb,
 
 		ac->ac_chain = i;
 		status = ocfs2_search_chain(ac, bits_wanted, min_bits,
-					    bit_off, num_bits,
-					    bg_blkno);
+					    bit_off, num_bits, bg_blkno,
+					    &bits_left);
 		if (!status)
 			break;
 		if (status < 0 && status != -ENOSPC) {
@@ -1260,8 +1370,19 @@ static int ocfs2_claim_suballoc_bits(struct ocfs2_super *osb,
 			goto bail;
 		}
 	}
-bail:
 
+set_hint:
+	if (status != -ENOSPC) {
+		/* If the next search of this group is not likely to
+		 * yield a suitable extent, then we reset the last
+		 * group hint so as to not waste a disk read */
+		if (bits_left < min_bits)
+			ac->ac_last_group = 0;
+		else
+			ac->ac_last_group = *bg_blkno;
+	}
+
+bail:
 	mlog_exit(status);
 	return status;
 }
@@ -1415,7 +1536,7 @@ int ocfs2_claim_clusters(struct ocfs2_super *osb,
 {
 	int status;
 	unsigned int bits_wanted = ac->ac_bits_wanted - ac->ac_bits_given;
-	u64 bg_blkno;
+	u64 bg_blkno = 0;
 	u16 bg_bit_off;
 
 	mlog_entry_void();

fs/ocfs2/suballoc.h

@@ -49,6 +49,8 @@ struct ocfs2_alloc_context {
 	u16    ac_chain;
 	int    ac_allow_chain_relink;
 	group_search_t *ac_group_search;
+
+	u64    ac_last_group;
 };
 
 void ocfs2_free_alloc_context(struct ocfs2_alloc_context *ac);