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/*
* SLOB Allocator: Simple List Of Blocks
*
* Matt Mackall <mpm@selenic.com> 12/30/03
*
* NUMA support by Paul Mundt, 2007.
*
* How SLOB works:
*
* The core of SLOB is a traditional K&R style heap allocator, with
* support for returning aligned objects. The granularity of this
* allocator is as little as 2 bytes, however typically most architectures
* will require 4 bytes on 32-bit and 8 bytes on 64-bit.
*
* The slob heap is a set of linked list of pages from alloc_pages(),
* and within each page, there is a singly-linked list of free blocks
* (slob_t). The heap is grown on demand. To reduce fragmentation,
* heap pages are segregated into three lists, with objects less than
* 256 bytes, objects less than 1024 bytes, and all other objects.
*
* Allocation from heap involves first searching for a page with
* sufficient free blocks (using a next-fit-like approach) followed by
* a first-fit scan of the page. Deallocation inserts objects back
* into the free list in address order, so this is effectively an
* address-ordered first fit.
*
* Above this is an implementation of kmalloc/kfree. Blocks returned
* from kmalloc are prepended with a 4-byte header with the kmalloc size.
* If kmalloc is asked for objects of PAGE_SIZE or larger, it calls
* alloc_pages() directly, allocating compound pages so the page order
* does not have to be separately tracked.
* These objects are detected in kfree() because PageSlab()
* is false for them.
*
* SLAB is emulated on top of SLOB by simply calling constructors and
* destructors for every SLAB allocation. Objects are returned with the
* 4-byte alignment unless the SLAB_HWCACHE_ALIGN flag is set, in which
* case the low-level allocator will fragment blocks to create the proper
* alignment. Again, objects of page-size or greater are allocated by
* calling alloc_pages(). As SLAB objects know their size, no separate
* size bookkeeping is necessary and there is essentially no allocation
* space overhead, and compound pages aren't needed for multi-page
* allocations.
*
* NUMA support in SLOB is fairly simplistic, pushing most of the real
* logic down to the page allocator, and simply doing the node accounting
* on the upper levels. In the event that a node id is explicitly
* provided, __alloc_pages_node() with the specified node id is used
* instead. The common case (or when the node id isn't explicitly provided)
* will default to the current node, as per numa_node_id().
*
* Node aware pages are still inserted in to the global freelist, and
* these are scanned for by matching against the node id encoded in the
* page flags. As a result, block allocations that can be satisfied from
* the freelist will only be done so on pages residing on the same node,
* in order to prevent random node placement.
*/
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/mm.h>
#include <linux/swap.h> /* struct reclaim_state */
#include <linux/cache.h>
#include <linux/init.h>
#include <linux/export.h>
#include <linux/rcupdate.h>
#include <linux/list.h>
#include <linux/kmemleak.h>
#include <trace/events/kmem.h>
#include <linux/atomic.h>
#include "slab.h"
/*
* slob_block has a field 'units', which indicates size of block if +ve,
* or offset of next block if -ve (in SLOB_UNITs).
*
* Free blocks of size 1 unit simply contain the offset of the next block.
* Those with larger size contain their size in the first SLOB_UNIT of
* memory, and the offset of the next free block in the second SLOB_UNIT.
*/
#if PAGE_SIZE <= (32767 * 2)
typedef s16 slobidx_t;
#else
typedef s32 slobidx_t;
#endif
struct slob_block {
slobidx_t units;
};
typedef struct slob_block slob_t;
/*
* All partially free slob pages go on these lists.
*/
#define SLOB_BREAK1 256
#define SLOB_BREAK2 1024
static LIST_HEAD(free_slob_small);
static LIST_HEAD(free_slob_medium);
static LIST_HEAD(free_slob_large);
/*
* slob_page_free: true for pages on free_slob_pages list.
*/
static inline int slob_page_free(struct page *sp)
{
return PageSlobFree(sp);
}
static void set_slob_page_free(struct page *sp, struct list_head *list)
{
list_add(&sp->lru, list);
__SetPageSlobFree(sp);
}
static inline void clear_slob_page_free(struct page *sp)
{
list_del(&sp->lru);
__ClearPageSlobFree(sp);
}
#define SLOB_UNIT sizeof(slob_t)
#define SLOB_UNITS(size) DIV_ROUND_UP(size, SLOB_UNIT)
/*
* struct slob_rcu is inserted at the tail of allocated slob blocks, which
* were created with a SLAB_TYPESAFE_BY_RCU slab. slob_rcu is used to free
* the block using call_rcu.
*/
struct slob_rcu {
struct rcu_head head;
int size;
};
/*
* slob_lock protects all slob allocator structures.
*/
static DEFINE_SPINLOCK(slob_lock);
/*
* Encode the given size and next info into a free slob block s.
*/
static void set_slob(slob_t *s, slobidx_t size, slob_t *next)
{
slob_t *base = (slob_t *)((unsigned long)s & PAGE_MASK);
slobidx_t offset = next - base;
if (size > 1) {
s[0].units = size;
s[1].units = offset;
} else
s[0].units = -offset;
}
/*
* Return the size of a slob block.
*/
static slobidx_t slob_units(slob_t *s)
{
if (s->units > 0)
return s->units;
return 1;
}
/*
* Return the next free slob block pointer after this one.
*/
static slob_t *slob_next(slob_t *s)
{
slob_t *base = (slob_t *)((unsigned long)s & PAGE_MASK);
slobidx_t next;
if (s[0].units < 0)
next = -s[0].units;
else
next = s[1].units;
return base+next;
}
/*
* Returns true if s is the last free block in its page.
*/
static int slob_last(slob_t *s)
{
return !((unsigned long)slob_next(s) & ~PAGE_MASK);
}
static void *slob_new_pages(gfp_t gfp, int order, int node)
{
void *page;
#ifdef CONFIG_NUMA
if (node != NUMA_NO_NODE)
page = __alloc_pages_node(node, gfp, order);
else
#endif
page = alloc_pages(gfp, order);
if (!page)
return NULL;
return page_address(page);
}
static void slob_free_pages(void *b, int order)
{
if (current->reclaim_state)
current->reclaim_state->reclaimed_slab += 1 << order;
free_pages((unsigned long)b, order);
}
/*
* Allocate a slob block within a given slob_page sp.
*/
static void *slob_page_alloc(struct page *sp, size_t size, int align)
{
slob_t *prev, *cur, *aligned = NULL;
int delta = 0, units = SLOB_UNITS(size);
for (prev = NULL, cur = sp->freelist; ; prev = cur, cur = slob_next(cur)) {
slobidx_t avail = slob_units(cur);
if (align) {
aligned = (slob_t *)ALIGN((unsigned long)cur, align);
delta = aligned - cur;
}
if (avail >= units + delta) { /* room enough? */
slob_t *next;
if (delta) { /* need to fragment head to align? */
next = slob_next(cur);
set_slob(aligned, avail - delta, next);
set_slob(cur, delta, aligned);
prev = cur;
cur = aligned;
avail = slob_units(cur);
}
next = slob_next(cur);
if (avail == units) { /* exact fit? unlink. */
if (prev)
set_slob(prev, slob_units(prev), next);
else
sp->freelist = next;
} else { /* fragment */
if (prev)
set_slob(prev, slob_units(prev), cur + units);
else
sp->freelist = cur + units;
set_slob(cur + units, avail - units, next);
}
sp->units -= units;
if (!sp->units)
clear_slob_page_free(sp);
return cur;
}
if (slob_last(cur))
return NULL;
}
}
/*
* slob_alloc: entry point into the slob allocator.
*/
static void *slob_alloc(size_t size, gfp_t gfp, int align, int node)
{
struct page *sp<
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