The patch titled
struct vfsmount: keep mnt_count & mnt_expiry_mark away from mnt_flags
has been removed from the -mm tree. Its filename was
struct-vfsmount-keep-mnt_count-mnt_expiry_mark-away-from-mnt_flags.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
Subject: struct vfsmount: keep mnt_count & mnt_expiry_mark away from mnt_flags
From: Eric Dumazet <dada1@xxxxxxxxxxxxx>
I noticed cache misses in touch_atime() that can be avoided if we keep
mnt_count & mnt_expiry_mark in a different cache line than mnt_flags
(mostly read)
mnt_count & mnt_expiry_mark are modified each time a file is opened/closed
in a file system.
touch_atime() is called each time a file is read, and generally needs to
read mnt_flags.
Other fields of struct vfsmount are mostly read so I chose to move
mnt_count & mnt_expiry_mark at the end of struct vfsmount. And adding a
comment so that nobody tries to re-arrange fields to fill the holes :)
On 64bits platforms, the new offsetof(mnt_count) is 0xC0
On 32bits platforms, it is 0x60, so I didnot add a
____cacheline_aligned_in_smp because it would have a too big impact on the
size of this object (in particular if CONFIG_X86_L1_CACHE_SHIFT=7)
Signed-off-by: Eric Dumazet <dada1@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mount.h | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff -puN include/linux/mount.h~struct-vfsmount-keep-mnt_count-mnt_expiry_mark-away-from-mnt_flags include/linux/mount.h
--- a/include/linux/mount.h~struct-vfsmount-keep-mnt_count-mnt_expiry_mark-away-from-mnt_flags
+++ a/include/linux/mount.h
@@ -43,9 +43,8 @@ struct vfsmount {
struct super_block *mnt_sb; /* pointer to superblock */
struct list_head mnt_mounts; /* list of children, anchored here */
struct list_head mnt_child; /* and going through their mnt_child */
- atomic_t mnt_count;
int mnt_flags;
- int mnt_expiry_mark; /* true if marked for expiry */
+ /* 4 bytes hole on 64bits arches */
char *mnt_devname; /* Name of device e.g. /dev/dsk/hda1 */
struct list_head mnt_list;
struct list_head mnt_expire; /* link in fs-specific expiry list */
@@ -54,6 +53,13 @@ struct vfsmount {
struct list_head mnt_slave; /* slave list entry */
struct vfsmount *mnt_master; /* slave is on master->mnt_slave_list */
struct mnt_namespace *mnt_ns; /* containing namespace */
+ /*
+ * We put mnt_count & mnt_expiry_mark at the end of struct vfsmount
+ * to let these frequently modified fields in a separate cache line
+ * (so that reads of mnt_flags wont ping-pong on SMP machines)
+ */
+ atomic_t mnt_count;
+ int mnt_expiry_mark; /* true if marked for expiry */
int mnt_pinned;
};
_
Patches currently in -mm which might be from dada1@xxxxxxxxxxxxx are
origin.patch
fs-speedup-rw_verify_area.patch
close_files-add-scheduling-point.patch
make-static-counters-in-new_inode-and-iunique-be-32-bits.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
