[merged] fs-optimize-inotify-fsnotify-code-for-unwatched-files.patch removed from -mm tree

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



The patch titled
     Subject: fs/notify: optimize inotify/fsnotify code for unwatched files
has been removed from the -mm tree.  Its filename was
     fs-optimize-inotify-fsnotify-code-for-unwatched-files.patch

This patch was dropped because it was merged into mainline or a subsystem tree

------------------------------------------------------
From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Subject: fs/notify: optimize inotify/fsnotify code for unwatched files

I have a _tiny_ microbenchmark that sits in a loop and writes single bytes
to a file.  Writing one byte to a tmpfs file is around 2x slower than
reading one byte from a file, which is a _bit_ more than I expecte.  This
is a dumb benchmark, but I think it's hard to deny that write() is a hot
path and we should avoid unnecessary overhead there.

I did a 'perf record' of 30-second samples of read and write.  The top
item in a diffprofile is srcu_read_lock() from fsnotify().  There are
active inotify fd's from systemd, but nothing is actually listening to the
file or its part of the filesystem.

I *think* we can avoid taking the srcu_read_lock() for the common case
where there are no actual marks on the file.  This means that there will
both be nothing to notify for *and* implies that there is no need for
clearing the ignore mask.

This patch gave a 13.1% speedup in writes/second on my test, which is an
improvement from the 10.8% that I saw with the last version.

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Eric Paris <eparis@xxxxxxxxxx>
Cc: John McCutchan <john@xxxxxxxxxxxxxxxxx>
Cc: Robert Love <rlove@xxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 fs/notify/fsnotify.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

diff -puN fs/notify/fsnotify.c~fs-optimize-inotify-fsnotify-code-for-unwatched-files fs/notify/fsnotify.c
--- a/fs/notify/fsnotify.c~fs-optimize-inotify-fsnotify-code-for-unwatched-files
+++ a/fs/notify/fsnotify.c
@@ -205,6 +205,16 @@ int fsnotify(struct inode *to_tell, __u3
 		mnt = NULL;
 
 	/*
+	 * Optimization: srcu_read_lock() has a memory barrier which can
+	 * be expensive.  It protects walking the *_fsnotify_marks lists.
+	 * However, if we do not walk the lists, we do not have to do
+	 * SRCU because we have no references to any objects and do not
+	 * need SRCU to keep them "alive".
+	 */
+	if (hlist_empty(&to_tell->i_fsnotify_marks) &&
+	    (!mnt || hlist_empty(&mnt->mnt_fsnotify_marks)))
+		return 0;
+	/*
 	 * if this is a modify event we may need to clear the ignored masks
 	 * otherwise return if neither the inode nor the vfsmount care about
 	 * this type of event.
_

Patches currently in -mm which might be from dave.hansen@xxxxxxxxxxxxxxx are

fs-do-not-prefault-sys_write-user-buffer-pages.patch

--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html



[Index of Archives]     [Kernel Newbies FAQ]     [Kernel Archive]     [IETF Annouce]     [DCCP]     [Netdev]     [Networking]     [Security]     [Bugtraq]     [Photo]     [Yosemite]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Linux SCSI]

  Powered by Linux