Author: mav
Date: Sun Jun 8 15:38:40 2014
New Revision: 267232
URL: http://svnweb.freebsd.org/changeset/base/267232
Log:
Use atomics to modify numvnodes variable.
This allows to mostly avoid lock usage in getnewvnode_[drop_]reserve(),
that reduces number of global vnode_free_list_mtx mutex acquisitions
from 4 to 2 per NFS request on ZFS, improving SMP scalability.
Reviewed by: kib
MFC after: 2 weeks
Sponsored by: iXsystems, Inc.
Modified:
head/sys/kern/vfs_subr.c
Modified: head/sys/kern/vfs_subr.c
==============================================================================
--- head/sys/kern/vfs_subr.c Sun Jun 8 14:02:25 2014 (r267231)
+++ head/sys/kern/vfs_subr.c Sun Jun 8 15:38:40 2014 (r267232)
@@ -995,14 +995,25 @@ void
getnewvnode_reserve(u_int count)
{
struct thread *td;
+ long num;
td = curthread;
+ /* First try to be quick and racy. */
+ if (numvnodes + count <= desiredvnodes) {
+ num = atomic_fetchadd_long(&numvnodes, count);
+ if (num + count <= desiredvnodes) {
+ td->td_vp_reserv += count;
+ return;
+ } else
+ atomic_subtract_long(&numvnodes, count);
+ }
+
mtx_lock(&vnode_free_list_mtx);
while (count > 0) {
if (getnewvnode_wait(0) == 0) {
count--;
td->td_vp_reserv++;
- numvnodes++;
+ atomic_add_long(&numvnodes, 1);
}
}
mtx_unlock(&vnode_free_list_mtx);
@@ -1014,10 +1025,7 @@ getnewvnode_drop_reserve(void)
struct thread *td;
td = curthread;
- mtx_lock(&vnode_free_list_mtx);
- KASSERT(numvnodes >= td->td_vp_reserv, ("reserve too large"));
- numvnodes -= td->td_vp_reserv;
- mtx_unlock(&vnode_free_list_mtx);
+ atomic_subtract_long(&numvnodes, td->td_vp_reserv);
td->td_vp_reserv = 0;
}
@@ -1054,7 +1062,7 @@ getnewvnode(const char *tag, struct moun
return (error);
}
#endif
- numvnodes++;
+ atomic_add_long(&numvnodes, 1);
mtx_unlock(&vnode_free_list_mtx);
alloc:
vp = (struct vnode *) uma_zalloc(vnode_zone, M_WAITOK|M_ZERO);
@@ -2385,9 +2393,7 @@ vdropl(struct vnode *vp)
* The vnode has been marked for destruction, so free it.
*/
CTR2(KTR_VFS, "%s: destroying the vnode %p", __func__, vp);
- mtx_lock(&vnode_free_list_mtx);
- numvnodes--;
- mtx_unlock(&vnode_free_list_mtx);
+ atomic_subtract_long(&numvnodes, 1);
bo = &vp->v_bufobj;
VNASSERT((vp->v_iflag & VI_FREE) == 0, vp,
("cleaned vnode still on the free list."));
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