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Commit 0ffc2a9c authored by Tejun Heo's avatar Tejun Heo Committed by Linus Torvalds
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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: default avatarTejun Heo <tj@kernel.org>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 54616283

include/linux/idr.h

+24 −1
Original line number Diff line number Diff line
@@ -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

lib/idr.c

+16 −22
Original line number Diff line number Diff line
@@ -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