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kref: Add a kref_sub function 

Makes it possible to optimize batched multiple unrefs.
Initial user will be drivers/gpu/ttm which accumulates unrefs to be
processed outside of atomic code.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
This commit is contained in:
Thomas Hellstrom 2010-11-16 15:21:07 +01:00 committed by Dave Airlie
parent d6ea88865d
commit ecf7ace9a8
2 changed files with 32 additions and 0 deletions
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2
include/linux/kref.h
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@ -24,5 +24,7 @@ struct kref {
void kref_init(struct kref *kref);
void kref_get(struct kref *kref);
int kref_put(struct kref *kref, void (*release) (struct kref *kref));
int kref_sub(struct kref *kref, unsigned int count,
void (*release) (struct kref *kref));
#endif /* _KREF_H_ */

30
lib/kref.c
View File

@ -62,6 +62,36 @@ int kref_put(struct kref *kref, void (*release)(struct kref *kref))
return 0;
}
/**
* kref_sub - subtract a number of refcounts for object.
* @kref: object.
* @count: Number of recounts to subtract.
* @release: pointer to the function that will clean up the object when the
* last reference to the object is released.
* This pointer is required, and it is not acceptable to pass kfree
* in as this function.
*
* Subtract @count from the refcount, and if 0, call release().
* Return 1 if the object was removed, otherwise return 0. Beware, if this
* function returns 0, you still can not count on the kref from remaining in
* memory. Only use the return value if you want to see if the kref is now
* gone, not present.
*/
int kref_sub(struct kref *kref, unsigned int count,
void (*release)(struct kref *kref))
{
WARN_ON(release == NULL);
WARN_ON(release == (void (*)(struct kref *))kfree);
if (atomic_sub_and_test((int) count, &kref->refcount)) {
release(kref);
return 1;
}
return 0;
}
EXPORT_SYMBOL(kref_init);
EXPORT_SYMBOL(kref_get);
EXPORT_SYMBOL(kref_put);
EXPORT_SYMBOL(kref_sub);