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authorTejun Heo <tj@kernel.org>2013-02-28 01:03:55 (GMT)
committerLinus Torvalds <torvalds@linux-foundation.org>2013-02-28 03:10:14 (GMT)
commitd5c7409f79e14db49d00785692334657592c07ff (patch)
tree9646f4a2934cf4d221f173c17defa22b90585e28 /lib/idr.c
parent3594eb2894f571c9b9a497159b1e4d84fdac5688 (diff)
idr: implement idr_preload[_end]() and idr_alloc()
The current idr interface is very cumbersome. * For all allocations, two function calls - idr_pre_get() and idr_get_new*() - should be made. * idr_pre_get() doesn't guarantee that the following idr_get_new*() will not fail from memory shortage. If idr_get_new*() returns -EAGAIN, the caller is expected to retry pre_get and allocation. * idr_get_new*() can't enforce upper limit. Upper limit can only be enforced by allocating and then freeing if above limit. * idr_layer buffer is unnecessarily per-idr. Each idr ends up keeping around MAX_IDR_FREE idr_layers. The memory consumed per idr is under two pages but it makes it difficult to make idr_layer larger. This patch implements the following new set of allocation functions. * idr_preload[_end]() - Similar to radix preload but doesn't fail. The first idr_alloc() inside preload section can be treated as if it were called with @gfp_mask used for idr_preload(). * idr_alloc() - Allocate an ID w/ lower and upper limits. Takes @gfp_flags and can be used w/o preloading. When used inside preloaded section, the allocation mask of preloading can be assumed. If idr_alloc() can be called from a context which allows sufficiently relaxed @gfp_mask, it can be used by itself. If, for example, idr_alloc() is called inside spinlock protected region, preloading can be used like the following. idr_preload(GFP_KERNEL); spin_lock(lock); id = idr_alloc(idr, ptr, start, end, GFP_NOWAIT); spin_unlock(lock); idr_preload_end(); if (id < 0) error; which is much simpler and less error-prone than idr_pre_get and idr_get_new*() loop. The new interface uses per-pcu idr_layer buffer and thus the number of idr's in the system doesn't affect the amount of memory used for preloading. idr_layer_alloc() is introduced to handle idr_layer allocations for both old and new ID allocation paths. This is a bit hairy now but the new interface is expected to replace the old and the internal implementation eventually will become simpler. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'lib/idr.c')
-rw-r--r--lib/idr.c174
1 files changed, 166 insertions, 8 deletions
diff --git a/lib/idr.c b/lib/idr.c
index b13aae5..2d016f5 100644
--- a/lib/idr.c
+++ b/lib/idr.c
@@ -35,8 +35,12 @@
#include <linux/string.h>
#include <linux/idr.h>
#include <linux/spinlock.h>
+#include <linux/percpu.h>
+#include <linux/hardirq.h>
static struct kmem_cache *idr_layer_cache;
+static DEFINE_PER_CPU(struct idr_layer *, idr_preload_head);
+static DEFINE_PER_CPU(int, idr_preload_cnt);
static DEFINE_SPINLOCK(simple_ida_lock);
static struct idr_layer *get_from_free_list(struct idr *idp)
@@ -54,6 +58,50 @@ static struct idr_layer *get_from_free_list(struct idr *idp)
return(p);
}
+/**
+ * idr_layer_alloc - allocate a new idr_layer
+ * @gfp_mask: allocation mask
+ * @layer_idr: optional idr to allocate from
+ *
+ * If @layer_idr is %NULL, directly allocate one using @gfp_mask or fetch
+ * one from the per-cpu preload buffer. If @layer_idr is not %NULL, fetch
+ * an idr_layer from @idr->id_free.
+ *
+ * @layer_idr is to maintain backward compatibility with the old alloc
+ * interface - idr_pre_get() and idr_get_new*() - and will be removed
+ * together with per-pool preload buffer.
+ */
+static struct idr_layer *idr_layer_alloc(gfp_t gfp_mask, struct idr *layer_idr)
+{
+ struct idr_layer *new;
+
+ /* this is the old path, bypass to get_from_free_list() */
+ if (layer_idr)
+ return get_from_free_list(layer_idr);
+
+ /* try to allocate directly from kmem_cache */
+ new = kmem_cache_zalloc(idr_layer_cache, gfp_mask);
+ if (new)
+ return new;
+
+ /*
+ * Try to fetch one from the per-cpu preload buffer if in process
+ * context. See idr_preload() for details.
+ */
+ if (in_interrupt())
+ return NULL;
+
+ preempt_disable();
+ new = __this_cpu_read(idr_preload_head);
+ if (new) {
+ __this_cpu_write(idr_preload_head, new->ary[0]);
+ __this_cpu_dec(idr_preload_cnt);
+ new->ary[0] = NULL;
+ }
+ preempt_enable();
+ return new;
+}
+
static void idr_layer_rcu_free(struct rcu_head *head)
{
struct idr_layer *layer;
@@ -139,6 +187,8 @@ EXPORT_SYMBOL(idr_pre_get);
* @starting_id: id to start search at
* @id: pointer to the allocated handle
* @pa: idr_layer[MAX_IDR_LEVEL] used as backtrack buffer
+ * @gfp_mask: allocation mask for idr_layer_alloc()
+ * @layer_idr: optional idr passed to idr_layer_alloc()
*
* Allocate an id in range [@starting_id, INT_MAX] from @idp without
* growing its depth. Returns
@@ -148,7 +198,8 @@ EXPORT_SYMBOL(idr_pre_get);
* -ENOSPC if the id space is exhausted,
* -ENOMEM if more idr_layers need to be allocated.
*/
-static int sub_alloc(struct idr *idp, int *starting_id, struct idr_layer **pa)
+static int sub_alloc(struct idr *idp, int *starting_id, struct idr_layer **pa,
+ gfp_t gfp_mask, struct idr *layer_idr)
{
int n, m, sh;
struct idr_layer *p, *new;
@@ -202,7 +253,7 @@ static int sub_alloc(struct idr *idp, int *starting_id, struct idr_layer **pa)
* Create the layer below if it is missing.
*/
if (!p->ary[m]) {
- new = get_from_free_list(idp);
+ new = idr_layer_alloc(gfp_mask, layer_idr);
if (!new)
return -ENOMEM;
new->layer = l-1;
@@ -218,7 +269,8 @@ static int sub_alloc(struct idr *idp, int *starting_id, struct idr_layer **pa)
}
static int idr_get_empty_slot(struct idr *idp, int starting_id,
- struct idr_layer **pa)
+ struct idr_layer **pa, gfp_t gfp_mask,
+ struct idr *layer_idr)
{
struct idr_layer *p, *new;
int layers, v, id;
@@ -229,7 +281,7 @@ build_up:
p = idp->top;
layers = idp->layers;
if (unlikely(!p)) {
- if (!(p = get_from_free_list(idp)))
+ if (!(p = idr_layer_alloc(gfp_mask, layer_idr)))
return -ENOMEM;
p->layer = 0;
layers = 1;
@@ -248,7 +300,7 @@ build_up:
p->layer++;
continue;
}
- if (!(new = get_from_free_list(idp))) {
+ if (!(new = idr_layer_alloc(gfp_mask, layer_idr))) {
/*
* The allocation failed. If we built part of
* the structure tear it down.
@@ -272,7 +324,7 @@ build_up:
}
rcu_assign_pointer(idp->top, p);
idp->layers = layers;
- v = sub_alloc(idp, &id, pa);
+ v = sub_alloc(idp, &id, pa, gfp_mask, layer_idr);
if (v == -EAGAIN)
goto build_up;
return(v);
@@ -312,7 +364,7 @@ int idr_get_new_above(struct idr *idp, void *ptr, int starting_id, int *id)
struct idr_layer *pa[MAX_IDR_LEVEL];
int rv;
- rv = idr_get_empty_slot(idp, starting_id, pa);
+ rv = idr_get_empty_slot(idp, starting_id, pa, 0, idp);
if (rv < 0)
return rv == -ENOMEM ? -EAGAIN : rv;
@@ -322,6 +374,112 @@ int idr_get_new_above(struct idr *idp, void *ptr, int starting_id, int *id)
}
EXPORT_SYMBOL(idr_get_new_above);
+/**
+ * idr_preload - preload for idr_alloc()
+ * @gfp_mask: allocation mask to use for preloading
+ *
+ * Preload per-cpu layer buffer for idr_alloc(). Can only be used from
+ * process context and each idr_preload() invocation should be matched with
+ * idr_preload_end(). Note that preemption is disabled while preloaded.
+ *
+ * The first idr_alloc() in the preloaded section can be treated as if it
+ * were invoked with @gfp_mask used for preloading. This allows using more
+ * permissive allocation masks for idrs protected by spinlocks.
+ *
+ * For example, if idr_alloc() below fails, the failure can be treated as
+ * if idr_alloc() were called with GFP_KERNEL rather than GFP_NOWAIT.
+ *
+ * idr_preload(GFP_KERNEL);
+ * spin_lock(lock);
+ *
+ * id = idr_alloc(idr, ptr, start, end, GFP_NOWAIT);
+ *
+ * spin_unlock(lock);
+ * idr_preload_end();
+ * if (id < 0)
+ * error;
+ */
+void idr_preload(gfp_t gfp_mask)
+{
+ /*
+ * Consuming preload buffer from non-process context breaks preload
+ * allocation guarantee. Disallow usage from those contexts.
+ */
+ WARN_ON_ONCE(in_interrupt());
+ might_sleep_if(gfp_mask & __GFP_WAIT);
+
+ preempt_disable();
+
+ /*
+ * idr_alloc() is likely to succeed w/o full idr_layer buffer and
+ * return value from idr_alloc() needs to be checked for failure
+ * anyway. Silently give up if allocation fails. The caller can
+ * treat failures from idr_alloc() as if idr_alloc() were called
+ * with @gfp_mask which should be enough.
+ */
+ while (__this_cpu_read(idr_preload_cnt) < MAX_IDR_FREE) {
+ struct idr_layer *new;
+
+ preempt_enable();
+ new = kmem_cache_zalloc(idr_layer_cache, gfp_mask);
+ preempt_disable();
+ if (!new)
+ break;
+
+ /* link the new one to per-cpu preload list */
+ new->ary[0] = __this_cpu_read(idr_preload_head);
+ __this_cpu_write(idr_preload_head, new);
+ __this_cpu_inc(idr_preload_cnt);
+ }
+}
+EXPORT_SYMBOL(idr_preload);
+
+/**
+ * idr_alloc - allocate new idr entry
+ * @idr: the (initialized) idr
+ * @ptr: pointer to be associated with the new id
+ * @start: the minimum id (inclusive)
+ * @end: the maximum id (exclusive, <= 0 for max)
+ * @gfp_mask: memory allocation flags
+ *
+ * Allocate an id in [start, end) and associate it with @ptr. If no ID is
+ * available in the specified range, returns -ENOSPC. On memory allocation
+ * failure, returns -ENOMEM.
+ *
+ * Note that @end is treated as max when <= 0. This is to always allow
+ * using @start + N as @end as long as N is inside integer range.
+ *
+ * The user is responsible for exclusively synchronizing all operations
+ * which may modify @idr. However, read-only accesses such as idr_find()
+ * or iteration can be performed under RCU read lock provided the user
+ * destroys @ptr in RCU-safe way after removal from idr.
+ */
+int idr_alloc(struct idr *idr, void *ptr, int start, int end, gfp_t gfp_mask)
+{
+ int max = end > 0 ? end - 1 : INT_MAX; /* inclusive upper limit */
+ struct idr_layer *pa[MAX_IDR_LEVEL];
+ int id;
+
+ might_sleep_if(gfp_mask & __GFP_WAIT);
+
+ /* sanity checks */
+ if (WARN_ON_ONCE(start < 0))
+ return -EINVAL;
+ if (unlikely(max < start))
+ return -ENOSPC;
+
+ /* allocate id */
+ id = idr_get_empty_slot(idr, start, pa, gfp_mask, NULL);
+ if (unlikely(id < 0))
+ return id;
+ if (unlikely(id > max))
+ return -ENOSPC;
+
+ idr_fill_slot(ptr, id, pa);
+ return id;
+}
+EXPORT_SYMBOL_GPL(idr_alloc);
+
static void idr_remove_warning(int id)
{
printk(KERN_WARNING
@@ -769,7 +927,7 @@ int ida_get_new_above(struct ida *ida, int starting_id, int *p_id)
restart:
/* get vacant slot */
- t = idr_get_empty_slot(&ida->idr, idr_id, pa);
+ t = idr_get_empty_slot(&ida->idr, idr_id, pa, 0, &ida->idr);
if (t < 0)
return t == -ENOMEM ? -EAGAIN : t;

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