Author: attilio
Date: Sun Feb 10 01:04:10 2013
New Revision: 246603
URL: http://svnweb.freebsd.org/changeset/base/246603
Log:
Remove a racy checks on resident and cached pages for
tmpfs_mapped{read, write}() functions:
- tmpfs_mapped{read, write}() are only called within VOP_{READ, WRITE}(),
which check before-hand to work only on valid VREG vnodes. Also the
vnode is locked for the duration of the work, making vnode reclaiming
impossible, during the operation. Hence, vobj can never be NULL.
- Currently check on resident pages and cached pages without vm object
lock held is racy and can do even more harm than good, as a page could
be transitioning between these 2 pools and then be skipped entirely.
Skip the checks as lookups on empty splay trees are very cheap.
Discussed with: alc
Tested by: flo
MFC after: 2 weeks
Modified:
head/sys/fs/tmpfs/tmpfs_vnops.c
Modified: head/sys/fs/tmpfs/tmpfs_vnops.c
==============================================================================
--- head/sys/fs/tmpfs/tmpfs_vnops.c Sat Feb 9 23:17:28 2013
(r246602)
+++ head/sys/fs/tmpfs/tmpfs_vnops.c Sun Feb 10 01:04:10 2013
(r246603)
@@ -511,10 +511,6 @@ tmpfs_mappedread(vm_object_t vobj, vm_ob
offset = addr & PAGE_MASK;
tlen = MIN(PAGE_SIZE - offset, len);
- if ((vobj == NULL) ||
- (vobj->resident_page_count == 0 && vobj->cache == NULL))
- goto nocache;
-
VM_OBJECT_LOCK(vobj);
lookupvpg:
if (((m = vm_page_lookup(vobj, idx)) != NULL) &&
@@ -569,7 +565,6 @@ lookupvpg:
return (error);
}
VM_OBJECT_UNLOCK(vobj);
-nocache:
error = tmpfs_nocacheread(tobj, idx, offset, tlen, uio);
return (error);
@@ -639,12 +634,6 @@ tmpfs_mappedwrite(vm_object_t vobj, vm_o
offset = addr & PAGE_MASK;
tlen = MIN(PAGE_SIZE - offset, len);
- if ((vobj == NULL) ||
- (vobj->resident_page_count == 0 && vobj->cache == NULL)) {
- vpg = NULL;
- goto nocache;
- }
-
VM_OBJECT_LOCK(vobj);
lookupvpg:
if (((vpg = vm_page_lookup(vobj, idx)) != NULL) &&
@@ -668,7 +657,6 @@ lookupvpg:
VM_OBJECT_UNLOCK(vobj);
vpg = NULL;
}
-nocache:
VM_OBJECT_LOCK(tobj);
tpg = vm_page_grab(tobj, idx, VM_ALLOC_WIRED |
VM_ALLOC_NORMAL | VM_ALLOC_RETRY);
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