idr_get_new() currently returns an incrementing counter in the top 8 bits of
the counter. Which means that most users have to mask it off again, and we
only have a 24-bit range.
So remove that counter. Also:
- Remove the BITS_PER_INT define due to namespace collision risk.
- Make MAX_ID_SHIFT 31, so counters have a 0 to 2G-1 range.
- Why is MAX_ID_SHIFT using sizeof(int) and not sizeof(long)? If it's for
consistency across 32- and 64-bit machines, why not just make it "31"?
- Does this still hold true with the counter removed?
/* We can only use half the bits in the top level because there are
only four possible bits in the top level (5 bits * 4 levels = 25
bits, but you only use 24 bits in the id). */
If not, what needs to change?
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/include/linux/idr.h | 18 +++++-------------
25-akpm/lib/idr.c | 19 +++----------------
2 files changed, 8 insertions(+), 29 deletions(-)
diff -puN include/linux/idr.h~idr-remove-counter include/linux/idr.h
--- 25/include/linux/idr.h~idr-remove-counter 2004-05-27 02:08:54.000011048 -0700
+++ 25-akpm/include/linux/idr.h 2004-05-27 02:08:54.006010136 -0700
@@ -11,8 +11,6 @@
#include <linux/types.h>
#include <asm/bitops.h>
-#define RESERVED_ID_BITS 8
-
#if BITS_PER_LONG == 32
# define IDR_BITS 5
# define IDR_FULL 0xfffffffful
@@ -32,11 +30,8 @@
#define IDR_SIZE (1 << IDR_BITS)
#define IDR_MASK ((1 << IDR_BITS)-1)
-/* Define the size of the id's */
-#define BITS_PER_INT (sizeof(int)*8)
-
-#define MAX_ID_SHIFT (BITS_PER_INT - RESERVED_ID_BITS)
-#define MAX_ID_BIT (1 << MAX_ID_SHIFT)
+#define MAX_ID_SHIFT (sizeof(int)*8 - 1)
+#define MAX_ID_BIT (1U << MAX_ID_SHIFT)
#define MAX_ID_MASK (MAX_ID_BIT - 1)
/* Leave the possibility of an incomplete final layer */
@@ -46,25 +41,23 @@
#define IDR_FREE_MAX MAX_LEVEL + MAX_LEVEL
struct idr_layer {
- unsigned long bitmap; /* A zero bit means "space here" */
+ unsigned long bitmap; /* A zero bit means "space here" */
struct idr_layer *ary[1<<IDR_BITS];
- int count; /* When zero, we can release it */
+ int count; /* When zero, we can release it */
};
struct idr {
struct idr_layer *top;
struct idr_layer *id_free;
- long count;
int layers;
int id_free_cnt;
spinlock_t lock;
};
-#define IDR_INIT(name) \
+#define IDR_INIT(name) \
{ \
.top = NULL, \
.id_free = NULL, \
- .count = 0, \
.layers = 0, \
.id_free_cnt = 0, \
.lock = SPIN_LOCK_UNLOCKED, \
@@ -82,4 +75,3 @@ void idr_remove(struct idr *idp, int id)
void idr_init(struct idr *idp);
extern kmem_cache_t *idr_layer_cache;
-
diff -puN lib/idr.c~idr-remove-counter lib/idr.c
--- 25/lib/idr.c~idr-remove-counter 2004-05-27 02:08:54.002010744 -0700
+++ 25-akpm/lib/idr.c 2004-05-27 02:08:54.007009984 -0700
@@ -27,15 +27,6 @@
* so you don't need to be too concerned about locking and conflicts
* with the slab allocator.
- * A word on reuse. We reuse empty id slots as soon as we can, always
- * using the lowest one available. But we also merge a counter in the
- * high bits of the id. The counter is RESERVED_ID_BITS (8 at this time)
- * long. This means that if you allocate and release the same id in a
- * loop we will reuse an id after about 256 times around the loop. The
- * word about is used here as we will NOT return a valid id of -1 so if
- * you loop on the largest possible id (and that is 24 bits, wow!) we
- * will kick the counter to avoid -1. (Paranoid? You bet!)
- *
* What you need to do is, since we don't keep the counter as part of
* id / ptr pair, to keep a copy of it in the pointed to structure
* (or else where) so that when you ask for a ptr you can varify that
@@ -78,7 +69,8 @@
* 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 a -ENOSPC. ptr is the pointer you want associated
- * with the id. The value is returned in the "id" field.
+ * with the id. The value is returned in the "id" field. idr_get_new()
+ * returns a value in the range 0 ... 0x7fffffff
* void *idr_find(struct idr *idp, int id);
@@ -271,12 +263,6 @@ build_up:
v = sub_alloc(idp, ptr, &id);
if (v == -2)
goto build_up;
- if ( likely(v >= 0 )) {
- idp->count++;
- v += (idp->count << MAX_ID_SHIFT);
- if ( unlikely( v == -1 ))
- v += (1L << MAX_ID_SHIFT);
- }
return(v);
}
EXPORT_SYMBOL(idr_get_new_above);
@@ -334,6 +320,7 @@ static void sub_remove(struct idr *idp,
idp->layers = 0;
}
}
+
void idr_remove(struct idr *idp, int id)
{
struct idr_layer *p;
_