Hi,
Thanks for the comments, Steve. Here is another version
that shows the same performance benefit (better, actually).
It's much simpler than the previous one. Instead of keeping
a bitmap, it simply uses a u32 in the gfs2_inode to keep
track of where it's last read-ahead. That avoids a lot of
the issues you wrote about.
I couldn't use the file struct because of the way function
gfs2_dir_read is called from NFS.
Regards,
Bob Peterson
Red Hat File Systems
Signed-off-by: Bob Peterson <rpete...@redhat.com>
--
fs/gfs2/dir.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
fs/gfs2/incore.h | 1 +
2 files changed, 51 insertions(+), 0 deletions(-)
diff --git a/fs/gfs2/dir.c b/fs/gfs2/dir.c
index 2045d70..31888bd 100644
--- a/fs/gfs2/dir.c
+++ b/fs/gfs2/dir.c
@@ -76,6 +76,8 @@
#define IS_LEAF 1 /* Hashed (leaf) directory */
#define IS_DINODE 2 /* Linear (stuffed dinode block) directory */
+#define MAX_RA_BLOCKS 32 /* max read-ahead blocks */
+
#define gfs2_disk_hash2offset(h) (((u64)(h)) >> 1)
#define gfs2_dir_offset2hash(p) ((u32)(((u64)(p)) << 1))
@@ -345,6 +347,7 @@ static __be64 *gfs2_dir_get_hash_table(struct gfs2_inode
*ip)
if (hc)
return hc;
+ ip->i_ra_index = 0;
hsize = 1 << ip->i_depth;
hsize *= sizeof(__be64);
if (hsize != i_size_read(&ip->i_inode)) {
@@ -382,6 +385,7 @@ static __be64 *gfs2_dir_get_hash_table(struct gfs2_inode
*ip)
void gfs2_dir_hash_inval(struct gfs2_inode *ip)
{
__be64 *hc = ip->i_hash_cache;
+ ip->i_ra_index = 0;
ip->i_hash_cache = NULL;
kfree(hc);
}
@@ -1377,6 +1381,50 @@ out:
}
+/* gfs2_dir_readahead - Issue read-ahead requests for leaf blocks.
+ *
+ * Note: we can't calculate each index like dir_e_read can because we don't
+ * have the leaf, and therefore we don't have the depth, and therefore we
+ * don't have the length. So we have to just read enough ahead to make up
+ * for the loss of information. */
+static void gfs2_dir_readahead(struct inode *inode, unsigned hsize, u32 index)
+{
+ struct gfs2_inode *ip = GFS2_I(inode);
+ struct gfs2_glock *gl = ip->i_gl;
+ struct buffer_head *bh;
+ u64 blocknr = 0, last;
+ unsigned count;
+
+ /* First check if we've already read-ahead for the whole range. */
+ if (index + MAX_RA_BLOCKS < ip->i_ra_index)
+ return;
+
+ ip->i_ra_index = max(index, ip->i_ra_index);
+ for (count = 0; count < MAX_RA_BLOCKS; count++) {
+ if (ip->i_ra_index >= hsize) /* if exceeded the hash table */
+ break;
+
+ last = blocknr;
+ blocknr = be64_to_cpu(ip->i_hash_cache[ip->i_ra_index]);
+ ip->i_ra_index++;
+ if (blocknr == last)
+ continue;
+
+ bh = gfs2_getbuf(gl, blocknr, 1);
+ if (trylock_buffer(bh)) {
+ if (buffer_uptodate(bh)) {
+ unlock_buffer(bh);
+ brelse(bh);
+ continue;
+ }
+ bh->b_end_io = end_buffer_read_sync;
+ submit_bh(READA | REQ_META, bh);
+ continue;
+ }
+ brelse(bh);
+ }
+}
+
/**
* dir_e_read - Reads the entries from a directory into a filldir buffer
* @dip: dinode pointer
@@ -1406,6 +1454,8 @@ static int dir_e_read(struct inode *inode, u64 *offset,
void *opaque,
if (IS_ERR(lp))
return PTR_ERR(lp);
+ gfs2_dir_readahead(inode, hsize, index);
+
while (index < hsize) {
error = gfs2_dir_read_leaf(inode, offset, opaque, filldir,
&copied, &depth,
diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index 892ac37..50c3bcb 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -286,6 +286,7 @@ struct gfs2_inode {
struct rw_semaphore i_rw_mutex;
struct list_head i_trunc_list;
__be64 *i_hash_cache;
+ u32 i_ra_index; /* read-ahead index */
u32 i_entries;
u32 i_diskflags;
u8 i_height;
