ocfs2: implement directory read-ahead
Uptodate.c now knows about read-ahead buffers. Use some more aggressive
logic in ocfs2_readdir().
The two functions which currently use directory read-ahead are
ocfs2_find_entry() and ocfs2_readdir().
Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>
diff --git a/fs/ocfs2/buffer_head_io.c b/fs/ocfs2/buffer_head_io.c
index 9a24adf..c903741 100644
--- a/fs/ocfs2/buffer_head_io.c
+++ b/fs/ocfs2/buffer_head_io.c
@@ -100,6 +100,9 @@
mlog_entry("(block=(%llu), nr=(%d), flags=%d, inode=%p)\n",
(unsigned long long)block, nr, flags, inode);
+ BUG_ON((flags & OCFS2_BH_READAHEAD) &&
+ (!inode || !(flags & OCFS2_BH_CACHED)));
+
if (osb == NULL || osb->sb == NULL || bhs == NULL) {
status = -EINVAL;
mlog_errno(status);
@@ -140,6 +143,30 @@
bh = bhs[i];
ignore_cache = 0;
+ /* There are three read-ahead cases here which we need to
+ * be concerned with. All three assume a buffer has
+ * previously been submitted with OCFS2_BH_READAHEAD
+ * and it hasn't yet completed I/O.
+ *
+ * 1) The current request is sync to disk. This rarely
+ * happens these days, and never when performance
+ * matters - the code can just wait on the buffer
+ * lock and re-submit.
+ *
+ * 2) The current request is cached, but not
+ * readahead. ocfs2_buffer_uptodate() will return
+ * false anyway, so we'll wind up waiting on the
+ * buffer lock to do I/O. We re-check the request
+ * with after getting the lock to avoid a re-submit.
+ *
+ * 3) The current request is readahead (and so must
+ * also be a caching one). We short circuit if the
+ * buffer is locked (under I/O) and if it's in the
+ * uptodate cache. The re-check from #2 catches the
+ * case that the previous read-ahead completes just
+ * before our is-it-in-flight check.
+ */
+
if (flags & OCFS2_BH_CACHED &&
!ocfs2_buffer_uptodate(inode, bh)) {
mlog(ML_UPTODATE,
@@ -169,6 +196,14 @@
continue;
}
+ /* A read-ahead request was made - if the
+ * buffer is already under read-ahead from a
+ * previously submitted request than we are
+ * done here. */
+ if ((flags & OCFS2_BH_READAHEAD)
+ && ocfs2_buffer_read_ahead(inode, bh))
+ continue;
+
lock_buffer(bh);
if (buffer_jbd(bh)) {
#ifdef CATCH_BH_JBD_RACES
@@ -181,13 +216,22 @@
continue;
#endif
}
+
+ /* Re-check ocfs2_buffer_uptodate() as a
+ * previously read-ahead buffer may have
+ * completed I/O while we were waiting for the
+ * buffer lock. */
+ if ((flags & OCFS2_BH_CACHED)
+ && !(flags & OCFS2_BH_READAHEAD)
+ && ocfs2_buffer_uptodate(inode, bh)) {
+ unlock_buffer(bh);
+ continue;
+ }
+
clear_buffer_uptodate(bh);
get_bh(bh); /* for end_buffer_read_sync() */
bh->b_end_io = end_buffer_read_sync;
- if (flags & OCFS2_BH_READAHEAD)
- submit_bh(READA, bh);
- else
- submit_bh(READ, bh);
+ submit_bh(READ, bh);
continue;
}
}
@@ -197,34 +241,39 @@
for (i = (nr - 1); i >= 0; i--) {
bh = bhs[i];
- /* We know this can't have changed as we hold the
- * inode sem. Avoid doing any work on the bh if the
- * journal has it. */
- if (!buffer_jbd(bh))
- wait_on_buffer(bh);
+ if (!(flags & OCFS2_BH_READAHEAD)) {
+ /* We know this can't have changed as we hold the
+ * inode sem. Avoid doing any work on the bh if the
+ * journal has it. */
+ if (!buffer_jbd(bh))
+ wait_on_buffer(bh);
- if (!buffer_uptodate(bh)) {
- /* Status won't be cleared from here on out,
- * so we can safely record this and loop back
- * to cleanup the other buffers. Don't need to
- * remove the clustered uptodate information
- * for this bh as it's not marked locally
- * uptodate. */
- status = -EIO;
- brelse(bh);
- bhs[i] = NULL;
- continue;
+ if (!buffer_uptodate(bh)) {
+ /* Status won't be cleared from here on out,
+ * so we can safely record this and loop back
+ * to cleanup the other buffers. Don't need to
+ * remove the clustered uptodate information
+ * for this bh as it's not marked locally
+ * uptodate. */
+ status = -EIO;
+ brelse(bh);
+ bhs[i] = NULL;
+ continue;
+ }
}
+ /* Always set the buffer in the cache, even if it was
+ * a forced read, or read-ahead which hasn't yet
+ * completed. */
if (inode)
ocfs2_set_buffer_uptodate(inode, bh);
}
if (inode)
mutex_unlock(&OCFS2_I(inode)->ip_io_mutex);
- mlog(ML_BH_IO, "block=(%llu), nr=(%d), cached=%s\n",
+ mlog(ML_BH_IO, "block=(%llu), nr=(%d), cached=%s, flags=0x%x\n",
(unsigned long long)block, nr,
- (!(flags & OCFS2_BH_CACHED) || ignore_cache) ? "no" : "yes");
+ (!(flags & OCFS2_BH_CACHED) || ignore_cache) ? "no" : "yes", flags);
bail: