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Subject[RFC PATCH 5/6] ext4: Search for an inode to update under the RCU lock if we can
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When we're updating timestamps in an inode, search for that inode under RCU
conditions to avoid holding the icache lock if we can.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: "Theodore Ts'o" <tytso@mit.edu>
cc: Andreas Dilger <adilger.kernel@dilger.ca>
cc: linux-ext4@vger.kernel.org
---

fs/ext4/inode.c | 41 +++++++++++++++++++++--------------------
1 file changed, 21 insertions(+), 20 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index b32a57bc5d5d..13e928ae70e5 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5144,21 +5144,23 @@ static int ext4_inode_blocks_set(handle_t *handle,
return 0;
}

-struct other_inode {
- unsigned long orig_ino;
- struct ext4_inode *raw_inode;
-};
-
-static int other_inode_match(struct inode * inode, unsigned long ino,
- void *data)
+static void __ext4_update_other_inode_time(struct super_block *sb,
+ unsigned long orig_ino,
+ unsigned long ino,
+ struct ext4_inode *raw_inode)
{
- struct other_inode *oi = (struct other_inode *) data;
+ struct inode *inode;
+
+ inode = find_inode_by_ino_rcu(sb, ino);
+ if (!inode)
+ return;

if ((inode->i_ino != ino) ||
(inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW |
I_DIRTY_INODE)) ||
((inode->i_state & I_DIRTY_TIME) == 0))
- return 0;
+ return;
+
spin_lock(&inode->i_lock);
if (((inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW |
I_DIRTY_INODE)) == 0) &&
@@ -5169,16 +5171,15 @@ static int other_inode_match(struct inode * inode, unsigned long ino,
spin_unlock(&inode->i_lock);

spin_lock(&ei->i_raw_lock);
- EXT4_INODE_SET_XTIME(i_ctime, inode, oi->raw_inode);
- EXT4_INODE_SET_XTIME(i_mtime, inode, oi->raw_inode);
- EXT4_INODE_SET_XTIME(i_atime, inode, oi->raw_inode);
- ext4_inode_csum_set(inode, oi->raw_inode, ei);
+ EXT4_INODE_SET_XTIME(i_ctime, inode, raw_inode);
+ EXT4_INODE_SET_XTIME(i_mtime, inode, raw_inode);
+ EXT4_INODE_SET_XTIME(i_atime, inode, raw_inode);
+ ext4_inode_csum_set(inode, raw_inode, ei);
spin_unlock(&ei->i_raw_lock);
- trace_ext4_other_inode_update_time(inode, oi->orig_ino);
- return -1;
+ trace_ext4_other_inode_update_time(inode, orig_ino);
+ return;
}
spin_unlock(&inode->i_lock);
- return -1;
}

/*
@@ -5188,24 +5189,24 @@ static int other_inode_match(struct inode * inode, unsigned long ino,
static void ext4_update_other_inodes_time(struct super_block *sb,
unsigned long orig_ino, char *buf)
{
- struct other_inode oi;
unsigned long ino;
int i, inodes_per_block = EXT4_SB(sb)->s_inodes_per_block;
int inode_size = EXT4_INODE_SIZE(sb);

- oi.orig_ino = orig_ino;
/*
* Calculate the first inode in the inode table block. Inode
* numbers are one-based. That is, the first inode in a block
* (assuming 4k blocks and 256 byte inodes) is (n*16 + 1).
*/
ino = ((orig_ino - 1) & ~(inodes_per_block - 1)) + 1;
+ rcu_read_lock();
for (i = 0; i < inodes_per_block; i++, ino++, buf += inode_size) {
if (ino == orig_ino)
continue;
- oi.raw_inode = (struct ext4_inode *) buf;
- (void) find_inode_nowait(sb, ino, other_inode_match, &oi);
+ __ext4_update_other_inode_time(sb, orig_ino, ino,
+ (struct ext4_inode *)buf);
}
+ rcu_read_unlock();
}

/*
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