Commit b12536c2 authored Sep 18, 2009 by Andi Kleen Committed by Al Viro Sep 24, 2009

vfs: optimization for touch_atime()



Some benchmark testing shows touch_atime to be high up in profile logs for
IO intensive workloads.  Most likely that's due to the lock in
mnt_want_write().  Unfortunately touch_atime first takes the lock, and
then does all the other tests that could avoid atime updates (like noatime
or relatime).

Do it the other way round -- first try to avoid the update and only then
if that didn't succeed take the lock.  That works because none of the
atime avoidance tests rely on locking.

This also eliminates a goto.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Cc: Christoph Hellwig <hch@infradead.org>
Reviewed-by: Valerie Aurora <vaurora@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

parent 22fe4042

fs/inode.c

+10 −10

Original line number	Diff line number	Diff line
		@@ -1416,31 +1416,31 @@ void touch_atime(struct vfsmount mnt, struct dentry dentry)
		struct inode *inode = dentry->d_inode;
		struct timespec now;

		if (mnt_want_write(mnt))
		return;
		if (inode->i_flags & S_NOATIME)
		goto out;
		return;
		if (IS_NOATIME(inode))
		goto out;
		return;
		if ((inode->i_sb->s_flags & MS_NODIRATIME) && S_ISDIR(inode->i_mode))
		goto out;
		return;

		if (mnt->mnt_flags & MNT_NOATIME)
		goto out;
		return;
		if ((mnt->mnt_flags & MNT_NODIRATIME) && S_ISDIR(inode->i_mode))
		goto out;
		return;

		now = current_fs_time(inode->i_sb);

		if (!relatime_need_update(mnt, inode, now))
		goto out;
		return;

		if (timespec_equal(&inode->i_atime, &now))
		goto out;
		return;

		if (mnt_want_write(mnt))
		return;

		inode->i_atime = now;
		mark_inode_dirty_sync(inode);
		out:
		mnt_drop_write(mnt);
		}
		EXPORT_SYMBOL(touch_atime);

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