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idr: implement lookup hint 

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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

25
include/linux/idr.h
View File

@ -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

38
lib/idr.c
View File

@ -137,8 +137,10 @@ static void idr_layer_rcu_free(struct rcu_head *head)
kmem_cache_free(idr_layer_cache, layer);
}
static inline void free_layer(struct idr_layer *p)
static inline void free_layer(struct idr *idr, struct idr_layer *p)
{
if (idr->hint && idr->hint == p)
RCU_INIT_POINTER(idr->hint, NULL);
call_rcu(&p->rcu_head, idr_layer_rcu_free);
}
@ -363,8 +365,12 @@ static int idr_get_empty_slot(struct idr *idp, int starting_id,
* @id and @pa are from a successful allocation from idr_get_empty_slot().
* Install the user pointer @ptr and mark the slot full.
*/
static void idr_fill_slot(void *ptr, int id, struct idr_layer **pa)
static void idr_fill_slot(struct idr *idr, void *ptr, int id,
struct idr_layer **pa)
{
/* update hint used for lookup, cleared from free_layer() */
rcu_assign_pointer(idr->hint, pa[0]);
rcu_assign_pointer(pa[0]->ary[id & IDR_MASK], (struct idr_layer *)ptr);
pa[0]->count++;
idr_mark_full(pa, id);
@ -397,7 +403,7 @@ int idr_get_new_above(struct idr *idp, void *ptr, int starting_id, int *id)
if (rv < 0)
return rv == -ENOMEM ? -EAGAIN : rv;
idr_fill_slot(ptr, rv, pa);
idr_fill_slot(idp, ptr, rv, pa);
*id = rv;
return 0;
}
@ -504,7 +510,7 @@ int idr_alloc(struct idr *idr, void *ptr, int start, int end, gfp_t gfp_mask)
if (unlikely(id > max))
return -ENOSPC;
idr_fill_slot(ptr, id, pa);
idr_fill_slot(idr, ptr, id, pa);
return id;
}
EXPORT_SYMBOL_GPL(idr_alloc);
@ -541,14 +547,14 @@ static void sub_remove(struct idr *idp, int shift, int id)
to_free = NULL;
while(*paa && ! --((**paa)->count)){
if (to_free)
free_layer(to_free);
free_layer(idp, to_free);
to_free = **paa;
**paa-- = NULL;
}
if (!*paa)
idp->layers = 0;
if (to_free)
free_layer(to_free);
free_layer(idp, to_free);
} else
idr_remove_warning(id);
}
@ -581,7 +587,7 @@ void idr_remove(struct idr *idp, int id)
--idp->layers;
to_free->count = 0;
bitmap_clear(to_free->bitmap, 0, IDR_SIZE);
free_layer(to_free);
free_layer(idp, to_free);
}
while (idp->id_free_cnt >= MAX_IDR_FREE) {
p = get_from_free_list(idp);
@ -622,7 +628,7 @@ void __idr_remove_all(struct idr *idp)
/* Get the highest bit that the above add changed from 0->1. */
while (n < fls(id ^ bt_mask)) {
if (p)
free_layer(p);
free_layer(idp, p);
n += IDR_BITS;
p = *--paa;
}
@ -655,19 +661,7 @@ void idr_destroy(struct idr *idp)
}
EXPORT_SYMBOL(idr_destroy);
/**
* 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.
*/
void *idr_find(struct idr *idp, int id)
void *idr_find_slowpath(struct idr *idp, int id)
{
int n;
struct idr_layer *p;
@ -691,7 +685,7 @@ void *idr_find(struct idr *idp, int id)
}
return((void *)p);
}
EXPORT_SYMBOL(idr_find);
EXPORT_SYMBOL(idr_find_slowpath);
/**
* idr_for_each - iterate through all stored pointers