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Remove a racy checks on resident and cached pages for

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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
This commit is contained in:
Attilio Rao 2013-02-10 01:04:10 +00:00
parent 3e3812572d
commit 5e60cb948e
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=246603
1 changed files with 0 additions and 12 deletions
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12
sys/fs/tmpfs/tmpfs_vnops.c
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@ -511,10 +511,6 @@ tmpfs_mappedread(vm_object_t vobj, vm_object_t tobj, size_t len, struct uio *uio
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 @@ tmpfs_mappedread(vm_object_t vobj, vm_object_t tobj, size_t len, struct uio *uio
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_object_t tobj, size_t len, struct uio *ui
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 @@ tmpfs_mappedwrite(vm_object_t vobj, vm_object_t tobj, size_t len, struct uio *ui
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);