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Reimplement IDR and IDA using the radix tree
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The IDR is very similar to the radix tree.  It has some functionality that
the radix tree did not have (alloc next free, cyclic allocation, a
callback-based for_each, destroy tree), which is readily implementable on
top of the radix tree.  A few small changes were needed in order to use a
tag to represent nodes with free space below them.  More extensive
changes were needed to support storing NULL as a valid entry in an IDR.
Plain radix trees still interpret NULL as a not-present entry.

The IDA is reimplemented as a client of the newly enhanced radix tree.  As
in the current implementation, it uses a bitmap at the last level of the
tree.

Signed-off-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Tested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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Matthew Wilcox committed Feb 14, 2017
1 parent 0ac398e commit 0a835c4
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Showing 13 changed files with 995 additions and 1,126 deletions.
145 changes: 65 additions & 80 deletions include/linux/idr.h
Original file line number Diff line number Diff line change
Expand Up @@ -12,47 +12,28 @@
#ifndef __IDR_H__
#define __IDR_H__

#include <linux/types.h>
#include <linux/bitops.h>
#include <linux/init.h>
#include <linux/rcupdate.h>
#include <linux/radix-tree.h>
#include <linux/gfp.h>

struct idr {
struct radix_tree_root idr_rt;
unsigned int idr_next;
};

/*
* Using 6 bits at each layer allows us to allocate 7 layers out of each page.
* 8 bits only gave us 3 layers out of every pair of pages, which is less
* efficient except for trees with a largest element between 192-255 inclusive.
* The IDR API does not expose the tagging functionality of the radix tree
* to users. Use tag 0 to track whether a node has free space below it.
*/
#define IDR_BITS 6
#define IDR_SIZE (1 << IDR_BITS)
#define IDR_MASK ((1 << IDR_BITS)-1)

struct idr_layer {
int prefix; /* the ID prefix of this idr_layer */
int layer; /* distance from leaf */
struct idr_layer __rcu *ary[1<<IDR_BITS];
int count; /* When zero, we can release it */
union {
/* A zero bit means "space here" */
DECLARE_BITMAP(bitmap, IDR_SIZE);
struct rcu_head rcu_head;
};
};
#define IDR_FREE 0

struct idr {
struct idr_layer __rcu *hint; /* the last layer allocated from */
struct idr_layer __rcu *top;
int layers; /* only valid w/o concurrent changes */
int cur; /* current pos for cyclic allocation */
spinlock_t lock;
int id_free_cnt;
struct idr_layer *id_free;
};
/* Set the IDR flag and the IDR_FREE tag */
#define IDR_RT_MARKER ((__force gfp_t)(3 << __GFP_BITS_SHIFT))

#define IDR_INIT(name) \
#define IDR_INIT \
{ \
.lock = __SPIN_LOCK_UNLOCKED(name.lock), \
.idr_rt = RADIX_TREE_INIT(IDR_RT_MARKER) \
}
#define DEFINE_IDR(name) struct idr name = IDR_INIT(name)
#define DEFINE_IDR(name) struct idr name = IDR_INIT

/**
* idr_get_cursor - Return the current position of the cyclic allocator
Expand All @@ -62,9 +43,9 @@ struct idr {
* idr_alloc_cyclic() if it is free (otherwise the search will start from
* this position).
*/
static inline unsigned int idr_get_cursor(struct idr *idr)
static inline unsigned int idr_get_cursor(const struct idr *idr)
{
return READ_ONCE(idr->cur);
return READ_ONCE(idr->idr_next);
}

/**
Expand All @@ -77,7 +58,7 @@ static inline unsigned int idr_get_cursor(struct idr *idr)
*/
static inline void idr_set_cursor(struct idr *idr, unsigned int val)
{
WRITE_ONCE(idr->cur, val);
WRITE_ONCE(idr->idr_next, val);
}

/**
Expand All @@ -97,22 +78,31 @@ static inline void idr_set_cursor(struct idr *idr, unsigned int val)
* period).
*/

/*
* This is what we export.
*/

void *idr_find_slowpath(struct idr *idp, int id);
void idr_preload(gfp_t gfp_mask);
int idr_alloc(struct idr *idp, void *ptr, int start, int end, gfp_t gfp_mask);
int idr_alloc_cyclic(struct idr *idr, void *ptr, int start, int end, gfp_t gfp_mask);
int idr_for_each(struct idr *idp,
int idr_alloc(struct idr *, void *entry, int start, int end, gfp_t);
int idr_alloc_cyclic(struct idr *, void *entry, int start, int end, gfp_t);
int idr_for_each(const struct idr *,
int (*fn)(int id, void *p, void *data), void *data);
void *idr_get_next(struct idr *idp, int *nextid);
void *idr_replace(struct idr *idp, void *ptr, int id);
void idr_remove(struct idr *idp, int id);
void idr_destroy(struct idr *idp);
void idr_init(struct idr *idp);
bool idr_is_empty(struct idr *idp);
void *idr_get_next(struct idr *, int *nextid);
void *idr_replace(struct idr *, void *, int id);
void idr_destroy(struct idr *);

static inline void idr_remove(struct idr *idr, int id)
{
radix_tree_delete(&idr->idr_rt, id);
}

static inline void idr_init(struct idr *idr)
{
INIT_RADIX_TREE(&idr->idr_rt, IDR_RT_MARKER);
idr->idr_next = 0;
}

static inline bool idr_is_empty(const struct idr *idr)
{
return radix_tree_empty(&idr->idr_rt) &&
radix_tree_tagged(&idr->idr_rt, IDR_FREE);
}

/**
* idr_preload_end - end preload section started with idr_preload()
Expand All @@ -137,77 +127,75 @@ static inline void idr_preload_end(void)
* 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)
static inline void *idr_find(const 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);
return radix_tree_lookup(&idr->idr_rt, id);
}

/**
* idr_for_each_entry - iterate over an idr's elements of a given type
* @idp: idr handle
* @idr: idr handle
* @entry: the type * to use as cursor
* @id: id entry's key
*
* @entry and @id do not need to be initialized before the loop, and
* after normal terminatinon @entry is left with the value NULL. This
* is convenient for a "not found" value.
*/
#define idr_for_each_entry(idp, entry, id) \
for (id = 0; ((entry) = idr_get_next(idp, &(id))) != NULL; ++id)
#define idr_for_each_entry(idr, entry, id) \
for (id = 0; ((entry) = idr_get_next(idr, &(id))) != NULL; ++id)

/**
* idr_for_each_entry - continue iteration over an idr's elements of a given type
* @idp: idr handle
* idr_for_each_entry_continue - continue iteration over an idr's elements of a given type
* @idr: idr handle
* @entry: the type * to use as cursor
* @id: id entry's key
*
* Continue to iterate over list of given type, continuing after
* the current position.
*/
#define idr_for_each_entry_continue(idp, entry, id) \
for ((entry) = idr_get_next((idp), &(id)); \
#define idr_for_each_entry_continue(idr, entry, id) \
for ((entry) = idr_get_next((idr), &(id)); \
entry; \
++id, (entry) = idr_get_next((idp), &(id)))
++id, (entry) = idr_get_next((idr), &(id)))

/*
* IDA - IDR based id allocator, use when translation from id to
* pointer isn't necessary.
*
* IDA_BITMAP_LONGS is calculated to be one less to accommodate
* ida_bitmap->nr_busy so that the whole struct fits in 128 bytes.
*/
#define IDA_CHUNK_SIZE 128 /* 128 bytes per chunk */
#define IDA_BITMAP_LONGS (IDA_CHUNK_SIZE / sizeof(long) - 1)
#define IDA_BITMAP_LONGS (IDA_CHUNK_SIZE / sizeof(long))
#define IDA_BITMAP_BITS (IDA_BITMAP_LONGS * sizeof(long) * 8)

struct ida_bitmap {
long nr_busy;
unsigned long bitmap[IDA_BITMAP_LONGS];
};

struct ida {
struct idr idr;
struct radix_tree_root ida_rt;
struct ida_bitmap *free_bitmap;
};

#define IDA_INIT(name) { .idr = IDR_INIT((name).idr), .free_bitmap = NULL, }
#define DEFINE_IDA(name) struct ida name = IDA_INIT(name)
#define IDA_INIT { \
.ida_rt = RADIX_TREE_INIT(IDR_RT_MARKER | GFP_NOWAIT), \
}
#define DEFINE_IDA(name) struct ida name = IDA_INIT

int ida_pre_get(struct ida *ida, gfp_t gfp_mask);
int ida_get_new_above(struct ida *ida, int starting_id, int *p_id);
void ida_remove(struct ida *ida, int id);
void ida_destroy(struct ida *ida);
void ida_init(struct ida *ida);

int ida_simple_get(struct ida *ida, unsigned int start, unsigned int end,
gfp_t gfp_mask);
void ida_simple_remove(struct ida *ida, unsigned int id);

static inline void ida_init(struct ida *ida)
{
INIT_RADIX_TREE(&ida->ida_rt, IDR_RT_MARKER | GFP_NOWAIT);
ida->free_bitmap = NULL;
}

/**
* ida_get_new - allocate new ID
* @ida: idr handle
Expand All @@ -220,11 +208,8 @@ static inline int ida_get_new(struct ida *ida, int *p_id)
return ida_get_new_above(ida, 0, p_id);
}

static inline bool ida_is_empty(struct ida *ida)
static inline bool ida_is_empty(const struct ida *ida)
{
return idr_is_empty(&ida->idr);
return radix_tree_empty(&ida->ida_rt);
}

void __init idr_init_cache(void);

#endif /* __IDR_H__ */
49 changes: 45 additions & 4 deletions include/linux/radix-tree.h
Original file line number Diff line number Diff line change
Expand Up @@ -105,7 +105,10 @@ struct radix_tree_node {
unsigned long tags[RADIX_TREE_MAX_TAGS][RADIX_TREE_TAG_LONGS];
};

/* root tags are stored in gfp_mask, shifted by __GFP_BITS_SHIFT */
/* The top bits of gfp_mask are used to store the root tags and the IDR flag */
#define ROOT_IS_IDR ((__force gfp_t)(1 << __GFP_BITS_SHIFT))
#define ROOT_TAG_SHIFT (__GFP_BITS_SHIFT + 1)

struct radix_tree_root {
gfp_t gfp_mask;
struct radix_tree_node __rcu *rnode;
Expand Down Expand Up @@ -358,10 +361,14 @@ int radix_tree_split(struct radix_tree_root *, unsigned long index,
unsigned new_order);
int radix_tree_join(struct radix_tree_root *, unsigned long index,
unsigned new_order, void *);
void **idr_get_free(struct radix_tree_root *, struct radix_tree_iter *,
gfp_t, int end);

#define RADIX_TREE_ITER_TAG_MASK 0x00FF /* tag index in lower byte */
#define RADIX_TREE_ITER_TAGGED 0x0100 /* lookup tagged slots */
#define RADIX_TREE_ITER_CONTIG 0x0200 /* stop at first hole */
enum {
RADIX_TREE_ITER_TAG_MASK = 0x0f, /* tag index in lower nybble */
RADIX_TREE_ITER_TAGGED = 0x10, /* lookup tagged slots */
RADIX_TREE_ITER_CONTIG = 0x20, /* stop at first hole */
};

/**
* radix_tree_iter_init - initialize radix tree iterator
Expand Down Expand Up @@ -402,6 +409,40 @@ radix_tree_iter_init(struct radix_tree_iter *iter, unsigned long start)
void **radix_tree_next_chunk(const struct radix_tree_root *,
struct radix_tree_iter *iter, unsigned flags);

/**
* radix_tree_iter_lookup - look up an index in the radix tree
* @root: radix tree root
* @iter: iterator state
* @index: key to look up
*
* If @index is present in the radix tree, this function returns the slot
* containing it and updates @iter to describe the entry. If @index is not
* present, it returns NULL.
*/
static inline void **radix_tree_iter_lookup(const struct radix_tree_root *root,
struct radix_tree_iter *iter, unsigned long index)
{
radix_tree_iter_init(iter, index);
return radix_tree_next_chunk(root, iter, RADIX_TREE_ITER_CONTIG);
}

/**
* radix_tree_iter_find - find a present entry
* @root: radix tree root
* @iter: iterator state
* @index: start location
*
* This function returns the slot containing the entry with the lowest index
* which is at least @index. If @index is larger than any present entry, this
* function returns NULL. The @iter is updated to describe the entry found.
*/
static inline void **radix_tree_iter_find(const struct radix_tree_root *root,
struct radix_tree_iter *iter, unsigned long index)
{
radix_tree_iter_init(iter, index);
return radix_tree_next_chunk(root, iter, 0);
}

/**
* radix_tree_iter_retry - retry this chunk of the iteration
* @iter: iterator state
Expand Down
3 changes: 1 addition & 2 deletions init/main.c
Original file line number Diff line number Diff line change
Expand Up @@ -553,7 +553,7 @@ asmlinkage __visible void __init start_kernel(void)
if (WARN(!irqs_disabled(),
"Interrupts were enabled *very* early, fixing it\n"))
local_irq_disable();
idr_init_cache();
radix_tree_init();

/*
* Allow workqueue creation and work item queueing/cancelling
Expand All @@ -568,7 +568,6 @@ asmlinkage __visible void __init start_kernel(void)
trace_init();

context_tracking_init();
radix_tree_init();
/* init some links before init_ISA_irqs() */
early_irq_init();
init_IRQ();
Expand Down
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