ext4: address scalability issue by removing extent cache statistics

BugLink: http://bugs.launchpad.net/bugs/987337

commit 9cd70b347e9761ea2d2ac3d758c529a48a8193e6 upstream.

Andi Kleen and Tim Chen have reported that under certain circumstances
the extent cache statistics are causing scalability problems due to
cache line bounces.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index dbae4d9..7b1cd5c 100644 (file)
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1185,9 +1185,6 @@ struct ext4_sb_info {
        unsigned long s_ext_blocks;
        unsigned long s_ext_extents;
 #endif
-       /* ext4 extent cache stats */
-       unsigned long extent_cache_hits;
-       unsigned long extent_cache_misses;
 
        /* for buddy allocator */
        struct ext4_group_info ***s_group_info;

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 7507036..c2a2012 100644 (file)
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -2052,10 +2052,6 @@ static int ext4_ext_check_cache(struct inode *inode, ext4_lblk_t block,
                ret = 1;
        }
 errout:
-       if (!ret)
-               sbi->extent_cache_misses++;
-       else
-               sbi->extent_cache_hits++;
        trace_ext4_ext_in_cache(inode, block, ret);
        spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
        return ret;

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 9281dbe..961059b 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2504,18 +2504,6 @@ static ssize_t lifetime_write_kbytes_show(struct ext4_attr *a,
                          EXT4_SB(sb)->s_sectors_written_start) >> 1)));
 }
 
-static ssize_t extent_cache_hits_show(struct ext4_attr *a,
-                                     struct ext4_sb_info *sbi, char *buf)
-{
-       return snprintf(buf, PAGE_SIZE, "%lu\n", sbi->extent_cache_hits);
-}
-
-static ssize_t extent_cache_misses_show(struct ext4_attr *a,
-                                       struct ext4_sb_info *sbi, char *buf)
-{
-       return snprintf(buf, PAGE_SIZE, "%lu\n", sbi->extent_cache_misses);
-}
-
 static ssize_t inode_readahead_blks_store(struct ext4_attr *a,
                                          struct ext4_sb_info *sbi,
                                          const char *buf, size_t count)
@@ -2573,8 +2561,6 @@ static struct ext4_attr ext4_attr_##name = __ATTR(name, mode, show, store)
 EXT4_RO_ATTR(delayed_allocation_blocks);
 EXT4_RO_ATTR(session_write_kbytes);
 EXT4_RO_ATTR(lifetime_write_kbytes);
-EXT4_RO_ATTR(extent_cache_hits);
-EXT4_RO_ATTR(extent_cache_misses);
 EXT4_ATTR_OFFSET(inode_readahead_blks, 0644, sbi_ui_show,
                 inode_readahead_blks_store, s_inode_readahead_blks);
 EXT4_RW_ATTR_SBI_UI(inode_goal, s_inode_goal);
@@ -2590,8 +2576,6 @@ static struct attribute *ext4_attrs[] = {
        ATTR_LIST(delayed_allocation_blocks),
        ATTR_LIST(session_write_kbytes),
        ATTR_LIST(lifetime_write_kbytes),
-       ATTR_LIST(extent_cache_hits),
-       ATTR_LIST(extent_cache_misses),
        ATTR_LIST(inode_readahead_blks),
        ATTR_LIST(inode_goal),
        ATTR_LIST(mb_stats),