| Message ID | 20230812123757.1666664-1-mjguzik@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | vfs: remove spin_lock_prefetch(&sb->s_inode_list_lock) from new_inode | expand |
On Sat, 12 Aug 2023 at 05:38, Mateusz Guzik <mjguzik@gmail.com> wrote: > > Also worth nothing is that this was the only remaining consumer. Send a patch that also includes just removing the definition of that thing, and I'll happily apply it. Linus
diff --git a/fs/inode.c b/fs/inode.c index 8fefb69e1f84..67611a360031 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -16,7 +16,6 @@ #include <linux/fsnotify.h> #include <linux/mount.h> #include <linux/posix_acl.h> -#include <linux/prefetch.h> #include <linux/buffer_head.h> /* for inode_has_buffers */ #include <linux/ratelimit.h> #include <linux/list_lru.h> @@ -1041,8 +1040,6 @@ struct inode *new_inode(struct super_block *sb) { struct inode *inode; - spin_lock_prefetch(&sb->s_inode_list_lock); - inode = new_inode_pseudo(sb); if (inode) inode_sb_list_add(inode);
It showed up in 2001, in the following commit in a historical repo [1]: commit c37fa164f793735b32aa3f53154ff1a7659e6442 Author: linus1 <torvalds@athlon.transmeta.com> Date: Thu Aug 16 11:00:00 2001 -0800 v2.4.9.9 -> v2.4.9.10 with a changelog which does not mention it. Since then the line got only touched up to keep compiling. While it may have been of benefit back in the day, it is guaranteed to at best not get in the way in the multicore setting -- as the code performs *a lot* of work between the prefetch and actual lock acquire, any contention means the cacheline is already invalid by the time the routine calls spin_lock(). It adds spurious traffic, for short. On top of it prefetch is notoriously tricky to use for single-threaded purposes, making it questionable from the get go. As such, remove it. I concede upfront I did not see value in benchmarking this change, but I can do it if that is deemed appropriate. Also worth nothing is that this was the only remaining consumer. [1] https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git/commit/fs/inode.c?id=c37fa164f793735b32aa3f53154ff1a7659e6442 Signed-off-by: Mateusz Guzik <mjguzik@gmail.com> --- fs/inode.c | 3 --- 1 file changed, 3 deletions(-)