nilfs2: improve execution time of NILFS_IOCTL_GET_CPINFO ioctl

The older a filesystem gets, the slower lscp command becomes.  This is
because nilfs_cpfile_do_get_cpinfo() function meets more hole blocks
as the start offset of valid checkpoint numbers gets bigger.

This reduces the overhead by skipping hole blocks efficiently with
nilfs_mdt_find_block() helper.

A measurement result of this patch is as follows:

Before:
$ time lscp
                 CNO        DATE     TIME  MODE  FLG      BLKCNT       ICNT
             5769303  2015-02-22 19:31:33   cp    -          108          1
             5769304  2015-02-22 19:38:54   cp    -          108          1

real    0m0.182s
user    0m0.003s
sys     0m0.180s

After:
$ time lscp
                 CNO        DATE     TIME  MODE  FLG      BLKCNT       ICNT
             5769303  2015-02-22 19:31:33   cp    -          108          1
             5769304  2015-02-22 19:38:54   cp    -          108          1

real    0m0.003s
user    0m0.001s
sys     0m0.002s

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 52 insertions, 6 deletions

diff --git a/fs/nilfs2/cpfile.c b/fs/nilfs2/cpfile.c
index 0d58075f34e2..b6596cab9e99 100644
--- a/fs/nilfs2/cpfile.c
+++ b/fs/nilfs2/cpfile.c
@@ -53,6 +53,13 @@ nilfs_cpfile_get_offset(const struct inode *cpfile, __u64 cno)
         return do_div(tcno, nilfs_cpfile_checkpoints_per_block(cpfile));
 }
 
+static __u64 nilfs_cpfile_first_checkpoint_in_block(const struct inode *cpfile,
+                                                    unsigned long blkoff)
+{
+        return (__u64)nilfs_cpfile_checkpoints_per_block(cpfile) * blkoff
+                + 1 - NILFS_MDT(cpfile)->mi_first_entry_offset;
+}
+
 static unsigned long
 nilfs_cpfile_checkpoints_in_block(const struct inode *cpfile,
                                   __u64 curr,
@@ -146,6 +153,44 @@ static inline int nilfs_cpfile_get_checkpoint_block(struct inode *cpfile,
                                    create, nilfs_cpfile_block_init, bhp);
 }
 
+/**
+ * nilfs_cpfile_find_checkpoint_block - find and get a buffer on cpfile
+ * @cpfile: inode of cpfile
+ * @start_cno: start checkpoint number (inclusive)
+ * @end_cno: end checkpoint number (inclusive)
+ * @cnop: place to store the next checkpoint number
+ * @bhp: place to store a pointer to buffer_head struct
+ *
+ * Return Value: On success, it returns 0. On error, the following negative
+ * error code is returned.
+ *
+ * %-ENOMEM - Insufficient memory available.
+ *
+ * %-EIO - I/O error
+ *
+ * %-ENOENT - no block exists in the range.
+ */
+static int nilfs_cpfile_find_checkpoint_block(struct inode *cpfile,
+                                              __u64 start_cno, __u64 end_cno,
+                                              __u64 *cnop,
+                                              struct buffer_head **bhp)
+{
+        unsigned long start, end, blkoff;
+        int ret;
+
+        if (unlikely(start_cno > end_cno))
+                return -ENOENT;
+
+        start = nilfs_cpfile_get_blkoff(cpfile, start_cno);
+        end = nilfs_cpfile_get_blkoff(cpfile, end_cno);
+
+        ret = nilfs_mdt_find_block(cpfile, start, end, &blkoff, bhp);
+        if (!ret)
+                *cnop = (blkoff == start) ? start_cno :
+                        nilfs_cpfile_first_checkpoint_in_block(cpfile, blkoff);
+        return ret;
+}
+
 static inline int nilfs_cpfile_delete_checkpoint_block(struct inode *cpfile,
                                                        __u64 cno)
 {
@@ -403,14 +448,15 @@ static ssize_t nilfs_cpfile_do_get_cpinfo(struct inode *cpfile, __u64 *cnop,
                 return -ENOENT; /* checkpoint number 0 is invalid */
         down_read(&NILFS_MDT(cpfile)->mi_sem);
 
-        for (n = 0; cno < cur_cno && n < nci; cno += ncps) {
-                ncps = nilfs_cpfile_checkpoints_in_block(cpfile, cno, cur_cno);
-                ret = nilfs_cpfile_get_checkpoint_block(cpfile, cno, 0, &bh);
+        for (n = 0; n < nci; cno += ncps) {
+                ret = nilfs_cpfile_find_checkpoint_block(
+                        cpfile, cno, cur_cno - 1, &cno, &bh);
                 if (ret < 0) {
-                        if (ret != -ENOENT)
-                                goto out;
-                        continue; /* skip hole */
+                        if (likely(ret == -ENOENT))
+                                break;
+                        goto out;
                 }
+                ncps = nilfs_cpfile_checkpoints_in_block(cpfile, cno, cur_cno);
 
                 kaddr = kmap_atomic(bh->b_page);
                 cp = nilfs_cpfile_block_get_checkpoint(cpfile, cno, bh, kaddr);