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SubjectRe: [PATCH 0/9] Scalability requirements for sysv ipc - v3
Paul E. McKenney wrote:
> On Wed, May 07, 2008 at 01:35:53PM +0200, Nadia.Derbey@bull.net 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@ccur.com
>> * 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@gmail.com>
>> */
>>
>>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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