ext4: allow inode_readahead_blks=0 (linux-2.6.37)

I cannot disable inode-read-ahead feature of ext4 (on 2.6.37):

# echo 0 > /sys/fs/ext4/sda2/inode_readahead_blks
bash: echo: write error: Invalid argument

On a server with lots of small files and random access this read-ahead makes
performance worse, and I'd like to disable it. I work around this problem
by using value of 1, but it still reads an extra block.

This patch fixes the problem by checking for zero explicitly.

Signed-off-by: Alexander V. Lukyanov <lav@netis.ru>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index ef83457fd4ead1f90885659f9c7ca8c1301a2790..a1ac24b6a758a1dfc9690ba297d75a18aebb3af1 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1771,7 +1771,7 @@ set_qf_format:
                                return 0;
                        if (option < 0 || option > (1 << 30))
                                return 0;
-                       if (!is_power_of_2(option)) {
+                       if (option && !is_power_of_2(option)) {
                                ext4_msg(sb, KERN_ERR,
                                         "EXT4-fs: inode_readahead_blks"
                                         " must be a power of 2");
@@ -2412,7 +2412,7 @@ static ssize_t inode_readahead_blks_store(struct ext4_attr *a,
        if (parse_strtoul(buf, 0x40000000, &t))
                return -EINVAL;
 
-       if (!is_power_of_2(t))
+       if (t && !is_power_of_2(t))
                return -EINVAL;
 
        sbi->s_inode_readahead_blks = t;