Re: [PATCH 0/9] Scalability requirements for sysv ipc - v3

From: Nadia Derbey
Date: Mon Jun 02 2008 - 01:52:55 EST

Paul E. McKenney wrote:
On Wed, May 07, 2008 at 01:35:53PM +0200, Nadia.Derbey@xxxxxxxx wrote:

After scalability problems have been detected when using the sysV ipcs, I
have proposed to use an RCU based implementation of the IDR api instead (see
threads http://lkml.org/lkml/2008/4/11/212 and
http://lkml.org/lkml/2008/4/29/295).

This resulted in many people asking to convert the idr API and make it
rcu safe (because most of the code was duplicated and thus unmaintanable
and unreviewable).

So here is a first attempt.

The important change wrt to the idr API itself is during idr removes:
idr layers are freed after a grace period, instead of being moved to the
free list.

The important change wrt to ipcs, is that idr_find() can now be called
locklessly inside a rcu read critical section.

Here are the results I've got for the pmsg test sent by Manfred:

2.6.25-rc3-mm1 2.6.25-rc3-mm1+ 2.6.25-mm1 Patched 2.6.25-mm1
1 1168441 1064021 876000 947488
2 1094264 921059 1549592 1730685
3 2082520 1738165 1694370 2324880
4 2079929 1695521 404553 2400408
5 2898758 406566 391283 3246580
6 2921417 261275 263249 3752148
7 3308761 126056 191742 4243142
8 3329456 100129 141722 4275780

1st column: stock 2.6.25-rc3-mm1
2nd column: 2.6.25-rc3-mm1 + ipc patches (store ipcs into idrs)
3nd column: stock 2.6.25-mm1
4th column: 2.6.25-mm1 + this pacth series.

I'll send a chart as an answer to this mail: don't know how to do that
with quilt :-(


Reviewers are more than ever welcome!

Patches should be applied on linux-2.6.25-mm1, in the following order:

[ PATCH 01/09 ] : idr_add_rcu_head.patch
[ PATCH 02/09 ] : idr_rename_routines.patch
[ PATCH 03/09 ] : idr_fix_printk.patch
[ PATCH 04/09 ] : idr_rc_to_errno.patch
[ PATCH 05/09 ] : idr_get_new_rcu_safe.patch
[ PATCH 06/09 ] : idr_find_rcu_safe.patch
[ PATCH 07/09 ] : idr_remove_rcu_safe.patch
[ PATCH 08/09 ] : ipc_fix_ipc_lock.patch
[ PATCH 09/09 ] : remove_ipc_lock_down.patch

Patches 2, 3 and 4 do not introduce actual changes.

I won't be available before next Tuesday, so, please, don't be mad at me if
I'm not answering fast enough.


I guess in my case, next Tuesday was not an issue. :-/

Anyway, thanks for reviewing the code!


Anyway, the idr.c changes look good to me. Not sure why you are using
INIT_RCU_HEAD() given that call_rcu() completely initializes the fields.
Using INIT_RCU_HEAD() doesn't cause any problems, but does add needless
code.

Well the INIT_RCU_HEAD calls are here because I first thought of moving the freed idr layers to the free list instead of directly removing them.
So the INIT_RCU_HEAD was a way for me to have a "blank" structure when getting a layer from the free list, i.e. reusing an old layer.
But I finally gave up the idea... but left the INI_RCU_HEAD() calls.
Will fix this.
But I have a "process" question: should I resend the complete patch series or would a patch above the already submitted ones be enough?

Regards,
Nadia


Commentary below, looks good from an RCU viewpoint.

Thanx, Paul


/*
* 2002-10-18 written by Jim Houston jim.houston@xxxxxxxx
* Copyright (C) 2002 by Concurrent Computer Corporation
* Distributed under the GNU GPL license version 2.
*
* Modified by George Anzinger to reuse immediately and to use
* find bit instructions. Also removed _irq on spinlocks.
*
* Modified by Nadia Derbey to make it RCU safe.
*
* Small id to pointer translation service.
*
* It uses a radix tree like structure as a sparse array indexed
* by the id to obtain the pointer. The bitmap makes allocating
* a new id quick.
*
* You call it to allocate an id (an int) an associate with that id a
* pointer or what ever, we treat it as a (void *). You can pass this
* id to a user for him to pass back at a later time. You then pass
* that id to this code and it returns your pointer.

* You can release ids at any time. When all ids are released, most of
* the memory is returned (we keep IDR_FREE_MAX) in a local pool so we
* don't need to go to the memory "store" during an id allocate, just
* so you don't need to be too concerned about locking and conflicts
* with the slab allocator.
*/

#ifndef TEST // to test in user space...
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/module.h>
#endif
#include <linux/err.h>
#include <linux/string.h>
#include <linux/idr.h>

static struct kmem_cache *idr_layer_cache;

static struct idr_layer *get_from_free_list(struct idr *idp)
{
struct idr_layer *p;
unsigned long flags;

spin_lock_irqsave(&idp->lock, flags);
if ((p = idp->id_free)) {
idp->id_free = p->ary[0];
idp->id_free_cnt--;
p->ary[0] = NULL;


OK, this is the freelist which is inaccessible to readers.


}
spin_unlock_irqrestore(&idp->lock, flags);
return(p);
}

static void idr_layer_rcu_free(struct rcu_head *head)
{
struct idr_layer *layer;

layer = container_of(head, struct idr_layer, rcu_head);
kmem_cache_free(idr_layer_cache, layer);
}

static inline void free_layer(struct idr_layer *p)
{
call_rcu(&p->rcu_head, idr_layer_rcu_free);
}

/* only called when idp->lock is held */
static void __move_to_free_list(struct idr *idp, struct idr_layer *p)
{
p->ary[0] = idp->id_free;


OK, this is the freelist which is inaccessible to readers.


idp->id_free = p;
idp->id_free_cnt++;
}

static void move_to_free_list(struct idr *idp, struct idr_layer *p)
{
unsigned long flags;

/*
* Depends on the return element being zeroed.
*/
spin_lock_irqsave(&idp->lock, flags);
__move_to_free_list(idp, p);
spin_unlock_irqrestore(&idp->lock, flags);
}

static void idr_mark_full(struct idr_layer **pa, int id)
{
struct idr_layer *p = pa[0];
int l = 0;

__set_bit(id & IDR_MASK, &p->bitmap);
/*
* If this layer is full mark the bit in the layer above to
* show that this part of the radix tree is full. This may
* complete the layer above and require walking up the radix
* tree.
*/
while (p->bitmap == IDR_FULL) {
if (!(p = pa[++l]))
break;
id = id >> IDR_BITS;
__set_bit((id & IDR_MASK), &p->bitmap);
}
}

/**
* idr_pre_get - reserver resources for idr allocation
* @idp: idr handle
* @gfp_mask: memory allocation flags
*
* This function should be called prior to locking and calling the
* idr_get_new* functions. It preallocates enough memory to satisfy
* the worst possible allocation.
*
* If the system is REALLY out of memory this function returns 0,
* otherwise 1.
*/
int idr_pre_get(struct idr *idp, gfp_t gfp_mask)
{
while (idp->id_free_cnt < IDR_FREE_MAX) {
struct idr_layer *new;
new = kmem_cache_alloc(idr_layer_cache, gfp_mask);
if (new == NULL)
return (0);
move_to_free_list(idp, new);
}
return 1;
}
EXPORT_SYMBOL(idr_pre_get);

static int sub_alloc(struct idr *idp, int *starting_id, struct idr_layer **pa)
{
int n, m, sh;
struct idr_layer *p, *new;
int l, id, oid;
unsigned long bm;

id = *starting_id;
restart:
p = idp->top;


OK, the caller presumably holds an update-side lock.


l = idp->layers;
pa[l--] = NULL;
while (1) {
/*
* We run around this while until we reach the leaf node...
*/
n = (id >> (IDR_BITS*l)) & IDR_MASK;
bm = ~p->bitmap;
m = find_next_bit(&bm, IDR_SIZE, n);
if (m == IDR_SIZE) {
/* no space available go back to previous layer. */
l++;
oid = id;
id = (id | ((1 << (IDR_BITS * l)) - 1)) + 1;

/* if already at the top layer, we need to grow */
if (!(p = pa[l])) {
*starting_id = id;
return IDR_NEED_TO_GROW;
}

/* If we need to go up one layer, continue the
* loop; otherwise, restart from the top.
*/
sh = IDR_BITS * (l + 1);
if (oid >> sh == id >> sh)
continue;
else
goto restart;
}
if (m != n) {
sh = IDR_BITS*l;
id = ((id >> sh) ^ n ^ m) << sh;
}
if ((id >= MAX_ID_BIT) || (id < 0))
return IDR_NOMORE_SPACE;
if (l == 0)
break;
/*
* Create the layer below if it is missing.
*/
if (!p->ary[m]) {


OK, we aren't dereferencing. Besides, we should hold the update-side
lock at this point.


new = get_from_free_list(idp);
if (!new)
return -1;
INIT_RCU_HEAD(&new->rcu_head);


Not needed, unless you want this zeroed for debug purposes.


rcu_assign_pointer(p->ary[m], new);
p->count++;
}
pa[l--] = p;
p = p->ary[m];


Holding update-side lock.


}

pa[l] = p;
return id;
}

static int idr_get_empty_slot(struct idr *idp, int starting_id,
struct idr_layer **pa)
{
struct idr_layer *p, *new;
int layers, v, id;
unsigned long flags;

id = starting_id;
build_up:
p = idp->top;


OK, the caller presumably holds an update-side lock.


layers = idp->layers;
if (unlikely(!p)) {
if (!(p = get_from_free_list(idp)))
return -1;
INIT_RCU_HEAD(&p->rcu_head);


Not needed, unless you want this zeroed for debug purposes.


layers = 1;
}
/*
* Add a new layer to the top of the tree if the requested
* id is larger than the currently allocated space.
*/
while ((layers < (MAX_LEVEL - 1)) && (id >= (1 << (layers*IDR_BITS)))) {
layers++;
if (!p->count)
continue;
if (!(new = get_from_free_list(idp))) {
/*
* The allocation failed. If we built part of
* the structure tear it down.
*/
spin_lock_irqsave(&idp->lock, flags);
for (new = p; p && p != idp->top; new = p) {
p = p->ary[0];
new->ary[0] = NULL;


OK, this presumably has not yet been made accessible to readers.


new->bitmap = new->count = 0;
__move_to_free_list(idp, new);
}
spin_unlock_irqrestore(&idp->lock, flags);
return -1;
}
new->ary[0] = p;


OK, this presumably has not yet been made accessible to readers.


new->count = 1;
INIT_RCU_HEAD(&new->rcu_head);


Not needed, unless you want this zeroed for debug purposes.


if (p->bitmap == IDR_FULL)
__set_bit(0, &new->bitmap);
p = new;
}
rcu_assign_pointer(idp->top, p);
idp->layers = layers;
v = sub_alloc(idp, &id, pa);
if (v == IDR_NEED_TO_GROW)
goto build_up;
return(v);
}

static int idr_get_new_above_int(struct idr *idp, void *ptr, int starting_id)
{
struct idr_layer *pa[MAX_LEVEL];
int id;

id = idr_get_empty_slot(idp, starting_id, pa);
if (id >= 0) {
/*
* Successfully found an empty slot. Install the user
* pointer and mark the slot full.
*/
rcu_assign_pointer(pa[0]->ary[id & IDR_MASK],
(struct idr_layer *)ptr);
pa[0]->count++;
idr_mark_full(pa, id);
}

return id;
}

/**
* idr_get_new_above - allocate new idr entry above or equal to a start id
* @idp: idr handle
* @ptr: pointer you want associated with the ide
* @start_id: id to start search at
* @id: pointer to the allocated handle
*
* This is the allocate id function. It should be called with any
* required locks.
*
* If memory is required, it will return -EAGAIN, you should unlock
* and go back to the idr_pre_get() call. If the idr is full, it will
* return -ENOSPC.
*
* @id returns a value in the range 0 ... 0x7fffffff
*/
int idr_get_new_above(struct idr *idp, void *ptr, int starting_id, int *id)
{
int rv;

rv = idr_get_new_above_int(idp, ptr, starting_id);
/*
* This is a cheap hack until the IDR code can be fixed to
* return proper error values.
*/
if (rv < 0)
return _idr_rc_to_errno(rv);
*id = rv;
return 0;
}
EXPORT_SYMBOL(idr_get_new_above);

/**
* idr_get_new - allocate new idr entry
* @idp: idr handle
* @ptr: pointer you want associated with the ide
* @id: pointer to the allocated handle
*
* This is the allocate id function. It should be called with any
* required locks.
*
* If memory is required, it will return -EAGAIN, you should unlock
* and go back to the idr_pre_get() call. If the idr is full, it will
* return -ENOSPC.
*
* @id returns a value in the range 0 ... 0x7fffffff
*/
int idr_get_new(struct idr *idp, void *ptr, int *id)
{
int rv;

rv = idr_get_new_above_int(idp, ptr, 0);
/*
* This is a cheap hack until the IDR code can be fixed to
* return proper error values.
*/
if (rv < 0)
return _idr_rc_to_errno(rv);
*id = rv;
return 0;
}
EXPORT_SYMBOL(idr_get_new);

static void idr_remove_warning(int id)
{
printk(KERN_WARNING
"idr_remove called for id=%d which is not allocated.\n", id);
dump_stack();
}

static void sub_remove(struct idr *idp, int shift, int id)
{
struct idr_layer *p = idp->top;


OK, the caller presumably holds an update-side lock.


struct idr_layer **pa[MAX_LEVEL];
struct idr_layer ***paa = &pa[0];
struct idr_layer *to_free;
int n;

*paa = NULL;
*++paa = &idp->top;

while ((shift > 0) && p) {
n = (id >> shift) & IDR_MASK;
__clear_bit(n, &p->bitmap);
*++paa = &p->ary[n];


OK, the caller presumably holds an update-side lock.


p = p->ary[n];
shift -= IDR_BITS;
}
n = id & IDR_MASK;
if (likely(p != NULL && test_bit(n, &p->bitmap))){
__clear_bit(n, &p->bitmap);
rcu_assign_pointer(p->ary[n], NULL);
to_free = NULL;
while(*paa && ! --((**paa)->count)){
if (to_free)
free_layer(to_free);
to_free = **paa;
**paa-- = NULL;
}
if (!*paa)
idp->layers = 0;
if (to_free)
free_layer(to_free);
} else
idr_remove_warning(id);
}

/**
* idr_remove - remove the given id and free it's slot
* @idp: idr handle
* @id: unique key
*/
void idr_remove(struct idr *idp, int id)
{
struct idr_layer *p;
struct idr_layer *to_free;

/* Mask off upper bits we don't use for the search. */
id &= MAX_ID_MASK;

sub_remove(idp, (idp->layers - 1) * IDR_BITS, id);
if (idp->top && idp->top->count == 1 && (idp->layers > 1) &&
idp->top->ary[0]) {


OK, the caller presumably holds the update-side lock.


/*
* Single child at leftmost slot: we can shrink the tree.
* This level is not needed anymore since when layers are
* inserted, they are inserted at the top of the existing
* tree.
*/
to_free = idp->top;
p = idp->top->ary[0];


OK, the caller presumably holds the update-side lock.


rcu_assign_pointer(idp->top, p);
--idp->layers;
to_free->bitmap = to_free->count = 0;
free_layer(to_free);
}
while (idp->id_free_cnt >= IDR_FREE_MAX) {
p = get_from_free_list(idp);
/*
* Note: we don't call the rcu callback here, since the only
* layers that fall into the freelist are those that have been
* preallocated.
*/
kmem_cache_free(idr_layer_cache, p);
}
return;
}
EXPORT_SYMBOL(idr_remove);

/**
* idr_remove_all - remove all ids from the given idr tree
* @idp: idr handle
*
* idr_destroy() only frees up unused, cached idp_layers, but this
* function will remove all id mappings and leave all idp_layers
* unused.
*
* A typical clean-up sequence for objects stored in an idr tree, will
* use idr_for_each() to free all objects, if necessay, then
* idr_remove_all() to remove all ids, and idr_destroy() to free
* up the cached idr_layers.
*/
void idr_remove_all(struct idr *idp)
{
int n, id, max;
struct idr_layer *p;
struct idr_layer *pa[MAX_LEVEL];
struct idr_layer **paa = &pa[0];

n = idp->layers * IDR_BITS;
p = idp->top;


OK, the caller presumably holds an update-side lock.


max = 1 << n;

id = 0;
while (id < max) {
while (n > IDR_BITS && p) {
n -= IDR_BITS;
*paa++ = p;
p = p->ary[(id >> n) & IDR_MASK];


OK, the caller presumably holds the update-side lock.


}

id += 1 << n;
while (n < fls(id)) {
if (p)
free_layer(p);
n += IDR_BITS;
p = *--paa;
}
}
rcu_assign_pointer(idp->top, NULL);
idp->layers = 0;
}
EXPORT_SYMBOL(idr_remove_all);

/**
* idr_destroy - release all cached layers within an idr tree
* idp: idr handle
*/
void idr_destroy(struct idr *idp)
{
while (idp->id_free_cnt) {
struct idr_layer *p = get_from_free_list(idp);
kmem_cache_free(idr_layer_cache, p);
}
}
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)
{
int n;
struct idr_layer *p;

n = idp->layers * IDR_BITS;
p = rcu_dereference(idp->top);

/* Mask off upper bits we don't use for the search. */
id &= MAX_ID_MASK;

if (id >= (1 << n))
return NULL;

while (n > 0 && p) {
n -= IDR_BITS;
p = rcu_dereference(p->ary[(id >> n) & IDR_MASK]);
}
return((void *)p);
}
EXPORT_SYMBOL(idr_find);

/**
* idr_for_each - iterate through all stored pointers
* @idp: idr handle
* @fn: function to be called for each pointer
* @data: data passed back to callback function
*
* Iterate over the pointers registered with the given idr. The
* callback function will be called for each pointer currently
* registered, passing the id, the pointer and the data pointer passed
* to this function. It is not safe to modify the idr tree while in
* the callback, so functions such as idr_get_new and idr_remove are
* not allowed.
*
* We check the return of @fn each time. If it returns anything other
* than 0, we break out and return that value.
*
* The caller must serialize idr_for_each() vs idr_get_new() and idr_remove().
*/
int idr_for_each(struct idr *idp,
int (*fn)(int id, void *p, void *data), void *data)
{
int n, id, max, error = 0;
struct idr_layer *p;
struct idr_layer *pa[MAX_LEVEL];
struct idr_layer **paa = &pa[0];

n = idp->layers * IDR_BITS;
p = rcu_dereference(idp->top);
max = 1 << n;

id = 0;
while (id < max) {
while (n > 0 && p) {
n -= IDR_BITS;
*paa++ = p;
p = rcu_dereference(p->ary[(id >> n) & IDR_MASK]);
}

if (p) {
error = fn(id, (void *)p, data);
if (error)
break;
}

id += 1 << n;
while (n < fls(id)) {
n += IDR_BITS;
p = *--paa;
}
}

return error;
}
EXPORT_SYMBOL(idr_for_each);

/**
* idr_replace - replace pointer for given id
* @idp: idr handle
* @ptr: pointer you want associated with the id
* @id: lookup key
*
* Replace the pointer registered with an id and return the old value.
* A -ENOENT return indicates that @id was not found.
* A -EINVAL return indicates that @id was not within valid constraints.
*
* The caller must serialize with writers.
*/
void *idr_replace(struct idr *idp, void *ptr, int id)
{
int n;
struct idr_layer *p, *old_p;

n = idp->layers * IDR_BITS;
p = idp->top;


OK, the caller presumably holds an update-side lock.


id &= MAX_ID_MASK;

if (id >= (1 << n))
return ERR_PTR(-EINVAL);

n -= IDR_BITS;
while ((n > 0) && p) {
p = p->ary[(id >> n) & IDR_MASK];


OK, the caller presumably holds the update-side lock.


n -= IDR_BITS;
}

n = id & IDR_MASK;
if (unlikely(p == NULL || !test_bit(n, &p->bitmap)))
return ERR_PTR(-ENOENT);

old_p = p->ary[n];


OK, the caller presumably holds the update-side lock.


rcu_assign_pointer(p->ary[n], ptr);

return old_p;
}
EXPORT_SYMBOL(idr_replace);

static void idr_cache_ctor(struct kmem_cache *idr_layer_cache, void *idr_layer)
{
memset(idr_layer, 0, sizeof(struct idr_layer));
}

void __init idr_init_cache(void)
{
idr_layer_cache = kmem_cache_create("idr_layer_cache",
sizeof(struct idr_layer), 0, SLAB_PANIC,
idr_cache_ctor);
}

/**
* idr_init - initialize idr handle
* @idp: idr handle
*
* This function is use to set up the handle (@idp) that you will pass
* to the rest of the functions.
*/
void idr_init(struct idr *idp)
{
memset(idp, 0, sizeof(struct idr));
spin_lock_init(&idp->lock);
}
EXPORT_SYMBOL(idr_init);


/*
* IDA - IDR based ID allocator
*
* this is id allocator without id -> pointer translation. Memory
* usage is much lower than full blown idr because each id only
* occupies a bit. ida uses a custom leaf node which contains
* IDA_BITMAP_BITS slots.
*
* 2007-04-25 written by Tejun Heo <htejun@xxxxxxxxx>
*/

static void free_bitmap(struct ida *ida, struct ida_bitmap *bitmap)
{
unsigned long flags;

if (!ida->free_bitmap) {
spin_lock_irqsave(&ida->idr.lock, flags);
if (!ida->free_bitmap) {
ida->free_bitmap = bitmap;
bitmap = NULL;
}
spin_unlock_irqrestore(&ida->idr.lock, flags);
}

kfree(bitmap);
}

/**
* ida_pre_get - reserve resources for ida allocation
* @ida: ida handle
* @gfp_mask: memory allocation flag
*
* This function should be called prior to locking and calling the
* following function. It preallocates enough memory to satisfy the
* worst possible allocation.
*
* If the system is REALLY out of memory this function returns 0,
* otherwise 1.
*/
int ida_pre_get(struct ida *ida, gfp_t gfp_mask)
{
/* allocate idr_layers */
if (!idr_pre_get(&ida->idr, gfp_mask))
return 0;

/* allocate free_bitmap */
if (!ida->free_bitmap) {
struct ida_bitmap *bitmap;

bitmap = kmalloc(sizeof(struct ida_bitmap), gfp_mask);
if (!bitmap)
return 0;

free_bitmap(ida, bitmap);
}

return 1;
}
EXPORT_SYMBOL(ida_pre_get);

/**
* ida_get_new_above - allocate new ID above or equal to a start id
* @ida: ida handle
* @staring_id: id to start search at
* @p_id: pointer to the allocated handle
*
* Allocate new ID above or equal to @ida. It should be called with
* any required locks.
*
* If memory is required, it will return -EAGAIN, you should unlock
* and go back to the ida_pre_get() call. If the ida is full, it will
* return -ENOSPC.
*
* @p_id returns a value in the range 0 ... 0x7fffffff.
*/
int ida_get_new_above(struct ida *ida, int starting_id, int *p_id)
{
struct idr_layer *pa[MAX_LEVEL];
struct ida_bitmap *bitmap;
unsigned long flags;
int idr_id = starting_id / IDA_BITMAP_BITS;
int offset = starting_id % IDA_BITMAP_BITS;
int t, id;

restart:
/* get vacant slot */
t = idr_get_empty_slot(&ida->idr, idr_id, pa);
if (t < 0)
return _idr_rc_to_errno(t);

if (t * IDA_BITMAP_BITS >= MAX_ID_BIT)
return -ENOSPC;

if (t != idr_id)
offset = 0;
idr_id = t;

/* if bitmap isn't there, create a new one */
bitmap = (void *)pa[0]->ary[idr_id & IDR_MASK];


OK, the caller presumably holds the update-side lock.


if (!bitmap) {
spin_lock_irqsave(&ida->idr.lock, flags);
bitmap = ida->free_bitmap;
ida->free_bitmap = NULL;
spin_unlock_irqrestore(&ida->idr.lock, flags);

if (!bitmap)
return -EAGAIN;

memset(bitmap, 0, sizeof(struct ida_bitmap));
rcu_assign_pointer(pa[0]->ary[idr_id & IDR_MASK],
(void *)bitmap);
pa[0]->count++;
}

/* lookup for empty slot */
t = find_next_zero_bit(bitmap->bitmap, IDA_BITMAP_BITS, offset);
if (t == IDA_BITMAP_BITS) {
/* no empty slot after offset, continue to the next chunk */
idr_id++;
offset = 0;
goto restart;
}

id = idr_id * IDA_BITMAP_BITS + t;
if (id >= MAX_ID_BIT)
return -ENOSPC;

__set_bit(t, bitmap->bitmap);
if (++bitmap->nr_busy == IDA_BITMAP_BITS)
idr_mark_full(pa, idr_id);

*p_id = id;

/* Each leaf node can handle nearly a thousand slots and the
* whole idea of ida is to have small memory foot print.
* Throw away extra resources one by one after each successful
* allocation.
*/
if (ida->idr.id_free_cnt || ida->free_bitmap) {
struct idr_layer *p = get_from_free_list(&ida->idr);
if (p)
kmem_cache_free(idr_layer_cache, p);
}

return 0;
}
EXPORT_SYMBOL(ida_get_new_above);

/**
* ida_get_new - allocate new ID
* @ida: idr handle
* @p_id: pointer to the allocated handle
*
* Allocate new ID. It should be called with any required locks.
*
* If memory is required, it will return -EAGAIN, you should unlock
* and go back to the idr_pre_get() call. If the idr is full, it will
* return -ENOSPC.
*
* @id returns a value in the range 0 ... 0x7fffffff.
*/
int ida_get_new(struct ida *ida, int *p_id)
{
return ida_get_new_above(ida, 0, p_id);
}
EXPORT_SYMBOL(ida_get_new);

/**
* ida_remove - remove the given ID
* @ida: ida handle
* @id: ID to free
*/
void ida_remove(struct ida *ida, int id)
{
struct idr_layer *p = ida->idr.top;
int shift = (ida->idr.layers - 1) * IDR_BITS;
int idr_id = id / IDA_BITMAP_BITS;
int offset = id % IDA_BITMAP_BITS;
int n;
struct ida_bitmap *bitmap;

/* clear full bits while looking up the leaf idr_layer */
while ((shift > 0) && p) {
n = (idr_id >> shift) & IDR_MASK;
__clear_bit(n, &p->bitmap);
p = p->ary[n];


OK, the caller presumably holds the update-side lock.


shift -= IDR_BITS;
}

if (p == NULL)
goto err;

n = idr_id & IDR_MASK;
__clear_bit(n, &p->bitmap);

bitmap = (void *)p->ary[n];


OK, the caller presumably holds the update-side lock.


if (!test_bit(offset, bitmap->bitmap))
goto err;

/* update bitmap and remove it if empty */
__clear_bit(offset, bitmap->bitmap);
if (--bitmap->nr_busy == 0) {
__set_bit(n, &p->bitmap); /* to please idr_remove() */
idr_remove(&ida->idr, idr_id);
free_bitmap(ida, bitmap);
}

return;

err:
printk(KERN_WARNING
"ida_remove called for id=%d which is not allocated.\n", id);
}
EXPORT_SYMBOL(ida_remove);

/**
* ida_destroy - release all cached layers within an ida tree
* ida: ida handle
*/
void ida_destroy(struct ida *ida)
{
idr_destroy(&ida->idr);
kfree(ida->free_bitmap);
}
EXPORT_SYMBOL(ida_destroy);

/**
* ida_init - initialize ida handle
* @ida: ida handle
*
* This function is use to set up the handle (@ida) that you will pass
* to the rest of the functions.
*/
void ida_init(struct ida *ida)
{
memset(ida, 0, sizeof(struct ida));
idr_init(&ida->idr);

}
EXPORT_SYMBOL(ida_init);

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