Author: mjg
Date: Sat Nov 30 16:40:16 2019
New Revision: 355226
URL: https://svnweb.freebsd.org/changeset/base/355226
Log:
vfs: swap placement between v_type and v_tag
The former is frequently accessed (e.g., in vfs_cache_lookup) and shares the
cacheline with v_usecount, avoidably adding to cache misses during concurrent
lookup. The latter is almost unused and probably can get garbage-collected.
The struct does not change in size despite enum vs char * discrepancy.
On 64-bit archs there used to be 4 bytes padding after v_type giving 480 bytes
in total.
Modified:
head/sys/sys/vnode.h
Modified: head/sys/sys/vnode.h
==============================================================================
--- head/sys/sys/vnode.h Sat Nov 30 14:17:45 2019 (r355225)
+++ head/sys/sys/vnode.h Sat Nov 30 16:40:16 2019 (r355226)
@@ -103,7 +103,7 @@ struct vnode {
* Fields which define the identity of the vnode. These fields are
* owned by the filesystem (XXX: and vgone() ?)
*/
- const char *v_tag; /* u type of underlying data */
+ enum vtype v_type; /* u vnode type */
struct vop_vector *v_op; /* u vnode operations vector */
void *v_data; /* u private data for fs */
@@ -173,7 +173,7 @@ struct vnode {
int v_writecount; /* I ref count of writers or
(negative) text users */
u_int v_hash;
- enum vtype v_type; /* u vnode type */
+ const char *v_tag; /* u type of underlying data */
};
#endif /* defined(_KERNEL) || defined(_KVM_VNODE) */
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