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idr: implement lookup hint

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While idr lookup isn't a particularly heavy operation, it still is too
substantial to use in hot paths without worrying about the performance
implications.  With recent changes, each idr_layer covers 256 slots
which should be enough to cover most use cases with single idr_layer
making lookup hint very attractive.

This patch adds idr->hint which points to the idr_layer which
allocated an ID most recently and the fast path lookup becomes

	if (look up target's prefix matches that of the hinted layer)
		return hint->ary[ID's offset in the leaf layer];

which can be inlined.

idr->hint is set to the leaf node on idr_fill_slot() and cleared from
free_layer().

[andriy.shevchenko@linux.intel.com: always do slow path when hint is uninitialized]
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Tejun Heo
2013-02-27 17:05:08 -08:00
committed by Linus Torvalds
parent 54616283c2
commit 0ffc2a9c80
2 changed files with 40 additions and 23 deletions
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25
include/linux/idr.h
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@@ -37,6 +37,7 @@ struct idr_layer {
};
struct idr {
struct idr_layer __rcu *hint; /* the last layer allocated from */
struct idr_layer __rcu *top;
struct idr_layer *id_free;
int layers; /* only valid w/o concurrent changes */
@@ -71,7 +72,7 @@ struct idr {
* This is what we export.
*/
void *idr_find(struct idr *idp, int id);
void *idr_find_slowpath(struct idr *idp, int id);
int idr_pre_get(struct idr *idp, gfp_t gfp_mask);
int idr_get_new_above(struct idr *idp, void *ptr, int starting_id, int *id);
void idr_preload(gfp_t gfp_mask);
@@ -96,6 +97,28 @@ static inline void idr_preload_end(void)
preempt_enable();
}
/**
* idr_find - return pointer for given id
* @idp: idr handle
* @id: lookup key
*
* Return the pointer given the id it has been registered with. A %NULL
* return indicates that @id is not valid or you passed %NULL in
* idr_get_new().
*
* This function can be called under rcu_read_lock(), given that the leaf
* pointers lifetimes are correctly managed.
*/
static inline void *idr_find(struct idr *idr, int id)
{
struct idr_layer *hint = rcu_dereference_raw(idr->hint);
if (hint && (id & ~IDR_MASK) == hint->prefix)
return rcu_dereference_raw(hint->ary[id & IDR_MASK]);
return idr_find_slowpath(idr, id);
}
/**
* idr_get_new - allocate new idr entry
* @idp: idr handle