/* -*- Mode: C; tab-width: 4; c-basic-offset: 4; indent-tabs-mode: nil -*- */
/*
* Slabs memory allocation, based on powers-of-N. Slabs are up to 1MB in size
* and are divided into chunks. The chunk sizes start off at the size of the
* "item" structure plus space for a small key and value. They increase by
* a multiplier factor from there, up to half the maximum slab size. The last
* slab size is always 1MB, since that's the maximum item size allowed by the
* memcached protocol.
*/
#include "memcached.h"
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/resource.h>
#include <fcntl.h>
#include <netinet/in.h>
#include <errno.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <signal.h>
#include <assert.h>
#include <pthread.h>
//#define DEBUG_SLAB_MOVER
/* powers-of-N allocation structures */
typedef struct {
unsigned int size; /* sizes of items */
unsigned int perslab; /* how many items per slab */
void *slots; /* list of item ptrs */
unsigned int sl_curr; /* total free items in list */
unsigned int slabs; /* how many slabs were allocated for this class */
void **slab_list; /* array of slab pointers */
unsigned int list_size; /* size of prev array */
size_t requested; /* The number of requested bytes */
} slabclass_t;
static slabclass_t slabclass[MAX_NUMBER_OF_SLAB_CLASSES];
static size_t mem_limit = 0;
static size_t mem_malloced = 0;
/* If the memory limit has been hit once. Used as a hint to decide when to
* early-wake the LRU maintenance thread */
static bool mem_limit_reached = false;
static int power_largest;
static void *mem_base = NULL;
static void *mem_current = NULL;
static size_t mem_avail = 0;
/**
* Access to the slab allocator is protected by this lock
*/
static pthread_mutex_t slabs_lock = PTHREAD_MUTEX_INITIALIZER;
static pthread_mutex_t slabs_rebalance_lock = PTHREAD_MUTEX_INITIALIZER;
/*
* Forward Declarations
*/
static int do_slabs_newslab(const unsigned int id);
static void *memory_allocate(size_t size);
static void do_slabs_free(void *ptr, const size_t size, unsigned int id);
/* Preallocate as many slab pages as possible (called from slabs_init)
on start-up, so users don't get confused out-of-memory errors when
they do have free (in-slab) space, but no space to make new slabs.
if maxslabs is 18 (POWER_LARGEST - POWER_SMALLEST + 1), then all
slab types can be made. if max memory is less than 18 MB, only the
smaller ones will be made. */
static void slabs_preallocate (const unsigned int maxslabs);
/*
* Figures out which slab class (chunk size) is required to store an item of
* a given size.
*
* Given object size, return id to use when allocating/freeing memory for object
* 0 means error: can't store such a large object
*/
unsigned int slabs_clsid(const size_t size) {
int res = POWER_SMALLEST;
if (size == 0 || size > settings.item_size_max)
return 0;
// commit: haizhu.shao 2016-12-03 19:17
// 习惯写成for循环
/**
for (; res != power_largest; ++res)
{
if (size <= slabclass[res].size)
break;
}
return res;
*
*/
while (size > slabclass[res].size)
if (res++ == power_largest) /* won't fit in the biggest slab */
return power_largest;
return res;
}
/**
* Determines the chunk sizes and initializes the slab class descriptors
* accordingly.
*/
void slabs_init(const size_t limit, const double factor, const bool prealloc, const uint32_t *slab_sizes) {
int i = POWER_SMALLEST - 1;
unsigned int size = sizeof(item) + settings.chunk_size;
mem_limit = limit;
if (prealloc) {
/* Allocate everything in a big chunk with malloc */
mem_base = malloc(mem_limit);
if (mem_base != NULL) {
mem_current = mem_base;
mem_avail = mem_limit;
} else {
fprintf(stderr, "Warning: Failed to allocate requested memory in"
" one large chunk.\nWill allocate in smaller chunks\n");
}
}
memset(slabclass, 0, sizeof(slabclass));
while (++i < MAX_NUMBER_OF_SLAB_CLASSES-1) {
if (slab_sizes != NULL) {
if (slab_sizes[i-1] == 0)
break;
size = slab_sizes[i-1];
} else if (size >= settings.slab_chunk_size_max / factor) {
break;
}
/* Make sure items are always n-byte aligned */
if (size % CHUNK_ALIGN_BYTES)
size += CHUNK_ALIGN_BYTES - (size % CHUNK_ALIGN_BYTES);
slabclass[i].size = size;
slabclass[i].perslab = settings.slab_page_size / slabclass[i].size;
if (slab_sizes == NULL)
size *= factor;
if (settings.verbose > 1) {
fprintf(stderr, "slab class %3d: chunk size %9u perslab %7u\n",
i, slabclass[i].size, slabclass[i].perslab);
}
}
power_largest = i;
slabclass[power_largest].size = settings.slab_chunk_size_max;
slabclass[power_largest].perslab = settings.slab_page_size / settings.slab_chunk_size_max;
if (settings.verbose > 1) {
fprintf(stderr, "slab class %3d: chunk size %9u perslab %7u\n",
i, slabclass[i].size, slabclass[i].perslab);
}
/* for the test suite: faking of how much we've already malloc'd */
{
char *t_initial_malloc = getenv("T_MEMD_INITIAL_MALLOC");
if (t_initial_malloc) {
mem_malloced = (size_t)atol(t_initial_malloc);
}
}
if (prealloc) {
slabs_preallocate(power_largest);
}
}
static void slabs_preallocate (const unsigned int maxslabs) {
int i;
unsigned int prealloc = 0;
/* pre-allocate a 1MB slab in every size class so people don't get
confused by non-intuitive "SERVER_ERROR out of memory"
messages. this is the most common question on the mailing
list. if you really don't want this, you can rebuild without
these three lines. */
for (i = POWER_SMALLEST; i < MAX_NUMBER_OF_SLAB_CLASSES; i++) {
if (++prealloc > maxslabs)
return;
if (do_slabs_newslab(i) == 0) {
fprintf(stderr, "Error while preallocating slab memory!\n"
"If using -L or other prealloc options, max memory must be "
"at least %d megabytes.\n", power_largest);
exit(1);
}
}
}
static int grow_slab_list (const unsigned int id) {
slabclass_t *p = &slabclass[id];
if (p->slabs == p->list_size) {
size_t new_size = (p->list_size != 0) ? p->list_size * 2 : 16;
void *new_list = realloc(p->slab_list, new_size * sizeof(void *));
if (new_list == 0) return 0;
p->list_size = new_size;
p->slab_list = new_list;
}
return 1;
}
static void split_slab_page_into_freelist(char *ptr, const unsigned int id) {
slabclass_t *p = &slabclass[id];
int x;
for (x = 0; x < p->perslab; x++) {
do_slabs_free(ptr, 0, id);
ptr += p->size;
}
}
/* Fast FIFO queue */
static void *get_page_from_global_pool(void) {
slabclass_t *p = &slabclass[SLAB_GLOBAL_PAGE_POOL];
if (p->slabs < 1) {
return NULL;
}
char *ret = p->slab_list[p->slabs - 1];
p->slabs--;
return ret;
}
static int do_slabs_newslab(const unsigned int id) {
slabclass_t *p = &slabclass[id];
slabclass_t *g = &slabclass[SLAB_GLOBAL_PAGE_POOL];
int len = (settings.slab_reassign || settings.slab_chunk_size_max != settings.slab_page_size)
? settings.slab_page_size
: p->size * p->perslab;
char *ptr;
if ((mem_limit && mem_malloced + len > mem_limit && p->slabs > 0
&& g->slabs == 0)) {
mem_limit_reached = true;
MEMCACHED_SLABS_SLABCLASS_ALLOCATE_FAILED(id);
return 0;
}
if ((grow_slab_list(id) == 0) ||
(((ptr = get_page_from_global_pool()) == NULL) &&
((ptr = memory_allocate((size_t)len)) == 0))) {
MEMCACHED_SLABS_SLABCLASS_ALLOCATE_FAILED(id);
return 0;
}
memset(ptr, 0, (size_t)len);
split_slab_page_into_freelist(ptr, id);
// commit: haizhu.shao 2016-12-03 20:50
// 這裡ptr是保存在slots的，沒有保存在slab_list裡面。
// 不懂這塊
p->slab_list[p->slabs++] = ptr;
MEMCACHED_SLABS_SLABCLASS_ALLOCATE(id);
return 1;
}
/* This calculation ends up adding sizeof(void *) to the item size. */
static void *do_slabs_alloc_chunked(const size_t size, slabclass_t *p, unsigned int id) {
void *ret = NULL;
item *it = NULL;
int x;
int csize = p->size - sizeof(item_chunk);
unsigned int chunks_req = size / csize;
if (size % csize != 0)
chunks_req++;
while (p->sl_curr < chunks_req) {
if (do_slabs_newslab(id) == 0)
break;
}
if (p->sl_curr >= chunks_req) {
item_chunk *chunk = NULL;
/* Configure the head item in the chain. */
it = (item *)p->slots;
p->slots = it->next;
if (it->next) it->next->prev = 0;
/* Squirrel away the "top chunk" into h_next for now */
it->h_next = (item *)p->slots;
assert(it->h_next != 0);
chunk = (item_chunk *) it->h_next;
/* roll down the chunks, marking them as such. */
for (x = 0; x < chunks_req-1; x++) {
chunk->it_flags &= ~ITEM_SLABBED;
chunk->it_flags |= ITEM_CHUNK;
/* Chunks always have a direct reference to the head item */
chunk->head = it;
chunk->size = p->size - sizeof(item_chunk);
chunk->used = 0;
chunk = chunk->next;
}
/* The final "next" is now the top of the slab freelist */
p->slots = chunk;
if (chunk && chunk->prev) {
/* Disconnect the final chunk from the chain */
chunk->prev->next = 0;
chunk->prev = 0;
}
it->it_flags &= ~ITEM_SLABBED;
it->it_flags |= ITEM_CHUNKED;
it->refcount = 1;
p->sl_curr -= chunks_req;
ret = (void *)it;
} else {
ret = NULL;
}
return ret;
}
/*@null@*/
static void *do_slabs_alloc(const size_t size, unsigned int id, uint64_t *total_bytes,
unsigned int flags) {
slabclass_t *p;
void *ret = NULL;
item *it = NULL;
if (id < POWER_SMALLEST || id > power_largest) {
MEMCACHED_SLABS_ALLOCATE_FAILED(size, 0);
return NULL;
}
p = &slabclass[id];
assert(p->sl_curr == 0 || ((item *)p->slots)->slabs_clsid == 0);
if (total_bytes != NULL) {
*total_bytes = p->requested;
}
if (size <= p->size) {
/* fail unless we have space at the end of a recently allocated page,
we have something on our freelist, or we could allocate a new page */
if (p->sl_curr == 0 && flags != SLABS_ALLOC_NO_NEWPAGE) {
do_slabs_newslab(id);
}
if (p->sl_curr != 0) {
/* return off our freelist */
it = (item *)p->slots;
p->slots = it->next;
if (it->next) it->next->prev = 0;
/* Kill flag and initialize refcount here for lock safety in slab
* mover's freeness detection. */
it->it_flags &= ~ITEM_SLABBED;
it->refcount = 1;
p->sl_curr--;
ret = (void *)it;
} else {
ret = NULL;
}
} else {
/* Dealing with a chunked item. */
ret = do_slabs_alloc_chunked(size, p, id);
}
if (ret) {
p->requested += size;
MEMCACHED_SLABS_ALLOCATE(size, id, p->size, ret);
} else {
MEMCACHED_SLABS_ALLOCATE_FAILED(size, id);
}
return ret;
}
// commit: haizhu.shao 2016-12-03 21:40
// TODO: alloc_chunk和free_chunk第一个chunk的分配不一样啊
// alloc_chunk时候并没有ITEM_data
static void do_slabs_free_chunked(item *it, const size_t size, unsigned int id,
slabclass_t *p) {
item_chunk *chunk = (item_chunk *) ITEM_data(it);
size_t realsize = size;
while (chunk) {
realsize += sizeof(item_chunk);
chunk = chunk->next;
}
chunk = (item_chunk *) ITEM_data(it);
unsigned int chunks_found = 1;
it->it_flags = ITEM_SLABBED;
it->slabs_clsid = 0;
it->prev = 0;
it->next = (item *) chunk->next;
assert(it->next);
/* top chunk should already point back to head */
assert(it->next && (void*)it->next->prev == (void*)chunk);
chunk = chunk->next;
chunk->prev = (item_chunk *)it;
while (chunk) {
assert(chunk->it_flags == ITEM_CHUNK);
chunk->it_flags = ITEM_SLABBED;
chunk->slabs_clsid = 0;
chunks_found++;
if (chunk->next) {
chunk = chunk->next;
} else {
break;
}
}
/* must have had nothing hanging off of the final chunk */
assert(chunk && chunk->next == 0);
/* Tail chunk, link the freelist here. */
chunk->next = p->slots;
if (chunk->next) chunk->next->prev = chunk;
p->slots = it;
p->sl_curr += chunks_found;
p->requested -= size;
return;
}
static void do_slabs_free(void *ptr, const size_t size, unsigned int id) {
slabclass_t *p;
item *it;
assert(id >= POWER_SMALLEST && id <= power_largest);
if (id < POWER_SMALLEST || id > power_largest)
return;
MEMCACHED_SLABS_FREE(size, id, ptr);
p = &slabclass[id];
it = (item *)ptr;
if ((it->it_flags & ITEM_CHUNKED) == 0) {
it->it_flags = ITEM_SLABBED;
it->slabs_clsid = 0;
it->prev = 0;
it->next = p->slots;
if (it->next) it->next->prev = it;
p->slots = it;
p->sl_curr++;
p->requested -= size;
} else {
do_slabs_free_chunked(it, size, id, p);
}
return;
}
static int nz_strcmp(int nzlength, const char *nz, const char *z) {
int zlength=strlen(z);
return (zlength == nzlength) && (strncmp(nz, z, zlength) == 0) ? 0 : -1;
}
bool get_stats(const char *stat_type, int nkey, ADD_STAT add_stats, void *c) {
bool ret = true;
if (add_stats != NULL) {
if (!stat_type) {
/* prepare general statistics for the engine */
STATS_LOCK();
APPEND_STAT("bytes", "%llu", (unsigned long long)stats_state.curr_bytes);
APPEND_STAT("curr_items", "%llu", (unsigned long long)stats_state.curr_items);
APPEND_STAT("total_items", "%llu", (unsigned long long)stats.total_items);
STATS_UNLOCK();
if (settings.slab_automove > 0) {
pthread_mutex_lock(&slabs_lock);
APPEND_STAT("slab_global_page_pool", "%u", slabclass[SLAB_GLOBAL_PAGE_POOL].slabs);
pthread_mutex_unlock(&slabs_lock);
}
item_stats_totals(add_stats, c);
} else if (nz_strcmp(nkey, stat_type, "items") == 0) {
item_stats(add_stats, c);
} else if (nz_strcmp(nkey, stat_type, "slabs") == 0) {
slabs_stats(add_stats, c);
} else if (nz_strcmp(nkey, stat_type, "sizes") == 0) {
item_stats_sizes(add_stats, c);
} else if (nz_strcmp(nkey, stat_type, "sizes_enable") == 0) {
item_stats_sizes_enable(add_stats, c);
} else if (nz_strcmp(nkey, stat_type, "sizes_disable") == 0) {
item_stats_sizes_disable(add_stats, c);
} else {
ret = false;
}
} else {
ret = false;
}
return ret;
}
/*@null@*/
static void do_slabs_stats(ADD_STAT add_stats, void *c) {
int i, total;
/* Get the per-thread stats which contain some interesting aggregates */
struct thread_stats thread_stats;
threadlocal_stats_aggregate(&thread_stats);
total = 0;
for(i = POWER_SMALLEST; i <= power_largest; i++) {
slabclass_t *p = &slabclass[i];
if (p->slabs != 0) {
uint32_t perslab, slabs;
slabs = p->slabs;
perslab = p->perslab;
char key_str[STAT_KEY_LEN];
char val_str[STAT_VAL_LEN];
int klen = 0, vlen = 0;
APPEND_NUM_STAT(i, "chunk_size", "%u", p->size);
APPEND_NUM_STAT(i, "chunks_per_page", "%u", perslab);
APPEND_NUM_STAT(i, "total_pages", "%u", slabs);
APPEND_NUM_STAT(i, "total_chunks", "%u", slabs * perslab);
APPEND_NUM_STAT(i, "used_chunks", "%u",
slabs*perslab - p->sl_curr);
APPEND_NUM_STAT(i, "free_chunks", "%u", p->sl_curr);
/* Stat is dead, but displaying zero instead of removing it. */
APPEND_NUM_STAT(i, "free_chunks_end", "%u", 0);
APPEND_NUM_STAT(i, "mem_requested", "%llu",
(unsigned long long)p->requested);
APPEND_NUM_STAT(i, "get_hits", "%llu",
(unsigned long long)thread_stats.slab_stats[i].get_hits);
APPEND_NUM_STAT(i, "cmd_set", "%llu",
(unsigned long long)thread_stats.slab_stats[i].set_cmds);
APPEND_NUM_STAT(i, "delete_hits", "%llu",
(unsigned long long)thread_stats.slab_stats[i].delete_hits);
APPEND_NUM_STAT(i, "incr_hits", "%llu",
(unsigned long long)thread_stats.slab_stats[i].incr_hits);
APPEND_NUM_STAT(i, "decr_hits", "%llu",
(unsigned long long)thread_stats.slab_stats[i].decr_hits);
APPEND_NUM_STAT(i, "cas_hits", "%llu",
(unsigned long long)thread_stats.slab_stats[i].cas_hits);
APPEND_NUM_STAT(i, "cas_badval", "%llu",
(unsigned long long)thread_stats.slab_stats[i].cas_badval);
APPEND_NUM_STAT(i, "touch_hits", "%llu",
(unsigned long long)thread_stats.slab_stats[i].touch_hits);
total++;
}
}
/* add overall slab stats and append terminator */
APPEND_STAT("active_slabs", "%d", total);
APPEND_STAT("total_malloced", "%llu", (unsigned long long)mem_malloced);
add_stats(NULL, 0, NULL, 0, c);
}
static void *memory_allocate(size_t size) {
void *ret;
if (mem_base == NULL) {
/* We are not using a preallocated large memory chunk */
ret = malloc(size);
} else {
ret = mem_current;
if (size > mem_avail) {
return NULL;
}
/* mem_current pointer _must_ be aligned!!! */
if (size % CHUNK_ALIGN_BYTES) {
size += CHUNK_ALIGN_BYTES - (size % CHUNK_ALIGN_BYTES);
}
mem_current = ((char*)mem_current) + size;
if (size < mem_avail) {
mem_avail -= size;
} else {
mem_avail = 0;
}
}
mem_malloced += size;
return ret;
}
/* Must only be used if all pages are item_size_max */
static void memory_release() {
void *p = NULL;
// commit: haizhu.shao 2016-12-03 21:45
// TODO: why?
if (mem_base != NULL)
return;
// commit: haizhu.shao 2016-12-03 21:45
// TODO: why? slab_reassign是啥东西
if (!settings.slab_reassign)
return;
while (mem_malloced > mem_limit &&
(p = get_page_from_global_pool()) != NULL) {
free(p);
mem_malloced -= settings.item_size_max;
}
}
void *slabs_alloc(size_t size, unsigned int id, uint64_t *total_bytes,
unsigned int flags) {
void *ret;
pthread_mutex_lock(&slabs_lock);
ret = do_slabs_alloc(size, id, total_bytes, flags);
pthread_mutex_unlock(&slabs_lock);
return ret;
}
void slabs_free(void *ptr, size_t size, unsigned int id) {
pthread_mutex_lock(&slabs_lock);
do_slabs_free(ptr, size, id);
pthread_mutex_unlock(&slabs_lock);
}
void slabs_stats(ADD_STAT add_stats, void *c) {
pthread_mutex_lock(&slabs_lock);
do_slabs_stats(add_stats, c);
pthread_mutex_unlock(&slabs_lock);
}
static bool do_slabs_adjust_mem_limit(size_t new_mem_limit) {
/* Cannot adjust memory limit at runtime if prealloc'ed */
if (mem_base != NULL)
return false;
settings.maxbytes = new_mem_limit;
mem_limit = new_mem_limit;
mem_limit_reached = false; /* Will reset on next alloc */
memory_release(); /* free what might already be in the global pool */
return true;
}
bool slabs_adjust_mem_limit(size_t new_mem_limit) {
bool ret;
pthread_mutex_lock(&slabs_lock);
ret = do_slabs_adjust_mem_limit(new_mem_limit);
pthread_mutex_unlock(&slabs_lock);
return ret;
}
// commit: haizhu.shao 2016-12-03 21:49
// TODO: 不懂这个函数的目的
void slabs_adjust_mem_requested(unsigned int id, size_t old, size_t ntotal)
{
pthread_mutex_lock(&slabs_lock);
slabclass_t *p;
if (id < POWER_SMALLEST || id > power_largest) {
fprintf(stderr, "Internal error! Invalid slab class\n");
abort();
}
p = &slabclass[id];
p->requested = p->requested - old + ntotal;
pthread_mutex_unlock(&slabs_lock);
}
unsigned int slabs_available_chunks(const unsigned int id, bool *mem_flag,
uint64_t *total_bytes, unsigned int *chunks_perslab) {
unsigned int ret;
slabclass_t *p;
pthread_mutex_lock(&slabs_lock);
p = &slabclass[id];
ret = p->sl_curr;
if (mem_flag != NULL)
*mem_flag = mem_limit_reached;
if (total_bytes != NULL)
*total_bytes = p->requested;
if (chunks_perslab != NULL)
*chunks_perslab = p->perslab;
pthread_mutex_unlock(&slabs_lock);
return ret;
}
static pthread_cond_t slab_rebalance_cond = PTHREAD_COND_INITIALIZER;
static volatile int do_run_slab_thread = 1;
static volatile int do_run_slab_rebalance_thread = 1;
#define DEFAULT_SLAB_BULK_CHECK 1
int slab_bulk_check = DEFAULT_SLAB_BULK_CHECK;
static int slab_rebalance_start(void) {
slabclass_t *s_cls;
int no_go = 0;
pthread_mutex_lock(&slabs_lock);
if (slab_rebal.s_clsid < POWER_SMALLEST ||
slab_rebal.s_clsid > power_largest ||
slab_rebal.d_clsid < SLAB_GLOBAL_PAGE_POOL ||
slab_rebal.d_clsid > power_largest ||
slab_rebal.s_clsid == slab_rebal.d_clsid)
no_go = -2;
s_cls = &slabclass[slab_rebal.s_clsid];
if (!grow_slab_list(slab_rebal.d_clsid)) {
no_go = -1;
}
if (s_cls->slabs < 2)
no_go = -3;
if (no_go != 0) {
pthread_mutex_unlock(&slabs_lock);
return no_go; /* Should use a wrapper function... */
}
/* Always kill the first available slab page as it is most likely to
* contain the oldest items
*/
slab_rebal.slab_start = s_cls->slab_list[0];
slab_rebal.slab_end = (char *)slab_rebal.slab_start +
(s_cls->size * s_cls->perslab);
slab_rebal.slab_pos = slab_rebal.slab_start;
slab_rebal.done = 0;
/* Also tells do_item_get to search for items in this slab */
slab_rebalance_signal = 2;
if (settings.verbose > 1) {
fprintf(stderr, "Started a slab rebalance\n");
}
pthread_mutex_unlock(&slabs_lock);
STATS_LOCK();
stats_state.slab_reassign_running = true;
STATS_UNLOCK();
return 0;
}
/* CALLED WITH slabs_lock HELD */
static void *slab_rebalance_alloc(const size_t size, unsigned int id) {
slabclass_t *s_cls;
s_cls = &slabclass[slab_rebal.s_clsid];
int x;
item *new_it = NULL;
for (x = 0; x < s_cls->perslab; x++) {
new_it = do_slabs_alloc(size, id, NULL, SLABS_ALLOC_NO_NEWPAGE);
/* check that memory isn't within the range to clear */
if (new_it == NULL) {
break;
}
if ((void *)new_it >= slab_rebal.slab_start
&& (void *)new_it < slab_rebal.slab_end) {
/* Pulled something we intend to free. Mark it as freed since
* we've already done the work of unlinking it from the freelist.
*/
s_cls->requested -= size;
new_it->refcount = 0;
new_it->it_flags = ITEM_SLABBED|ITEM_FETCHED;
#ifdef DEBUG_SLAB_MOVER
memcpy(ITEM_key(new_it), "deadbeef", 8);
#endif
new_it = NULL;
slab_rebal.inline_reclaim++;
} else {
break;
}
}
return new_it;
}
/* CALLED WITH slabs_lock HELD */
/* detatches item/chunk from freelist. */
static void slab_rebalance_cut_free(slabclass_t *s_cls, item *it) {
/* Ensure this was on the freelist and nothing else. */
assert(it->it_flags == ITEM_SLABBED);
if (s_cls->slots == it) {
s_cls->slots = it->next;
}
if (it->next) it->next->prev = it->prev;
if (it->prev) it->prev->next = it->next;
s_cls->sl_curr--;
}
enum move_status {
MOVE_PASS=0, MOVE_FROM_SLAB, MOVE_FROM_LRU, MOVE_BUSY, MOVE_LOCKED
};
/* refcount == 0 is safe since nobody can incr while item_lock is held.
* refcount != 0 is impossible since flags/etc can be modified in other
* threads. instead, note we found a busy one and bail. logic in do_item_get
* will prevent busy items from continuing to be busy
* NOTE: This is checking it_flags outside of an item lock. I believe this
* works since it_flags is 8 bits, and we're only ever comparing a single bit
* regardless. ITEM_SLABBED bit will always be correct since we're holding the
* lock which modifies that bit. ITEM_LINKED won't exist if we're between an
* item having ITEM_SLABBED removed, and the key hasn't been added to the item
* yet. The memory barrier from the slabs lock should order the key write and the
* flags to the item?
* If ITEM_LINKED did exist and was just removed, but we still see it, that's
* still safe since it will have a valid key, which we then lock, and then
* recheck everything.
* This may not be safe on all platforms; If not, slabs_alloc() will need to
* seed the item key while holding slabs_lock.
*/
static int slab_rebalance_move(void) {
slabclass_t *s_cls;
int x;
int was_busy = 0;
int refcount = 0;
uint32_t hv;
void *hold_lock;
enum move_status status = MOVE_PASS;
pthread_mutex_lock(&slabs_lock);
s_cls = &slabclass[slab_rebal.s_clsid];
for (x = 0; x < slab_bulk_check; x++) {
hv = 0;
hold_lock = NULL;
item *it = slab_rebal.slab_pos;
item_chunk *ch = NULL;
status = MOVE_PASS;
if (it->it_flags & ITEM_CHUNK) {
/* This chunk is a chained part of a larger item. */
ch = (item_chunk *) it;
/* Instead, we use the head chunk to find the item and effectively
* lock the entire structure. If a chunk has ITEM_CHUNK flag, its
* head cannot be slabbed, so the normal routine is safe. */
it = ch->head;
assert(it->it_flags & ITEM_CHUNKED);
}
/* ITEM_FETCHED when ITEM_SLABBED is overloaded to mean we've cleared
* the chunk for move. Only these two flags should exist.
*/
if (it->it_flags != (ITEM_SLABBED|ITEM_FETCHED)) {
/* ITEM_SLABBED can only be added/removed under the slabs_lock */
if (it->it_flags & ITEM_SLABBED) {
assert(ch == NULL);
slab_rebalance_cut_free(s_cls, it);
status = MOVE_FROM_SLAB;
} else if ((it->it_flags & ITEM_LINKED) != 0) {
/* If it doesn't have ITEM_SLABBED, the item could be in any
* state on its way to being freed or written to. If no
* ITEM_SLABBED, but it's had ITEM_LINKED, it must be active
* and have the key written to it already.
*/
hv = hash(ITEM_key(it), it->nkey);
if ((hold_lock = item_trylock(hv)) == NULL) {
status = MOVE_LOCKED;
} else {
refcount = refcount_incr(&it->refcount);
if (refcount == 2) { /* item is linked but not busy */
/* Double check ITEM_LINKED flag here, since we're
* past a memory barrier from the mutex. */
if ((it->it_flags & ITEM_LINKED) != 0) {
status = MOVE_FROM_LRU;
} else {
/* refcount == 1 + !ITEM_LINKED means the item is being
* uploaded to, or was just unlinked but hasn't been freed
* yet. Let it bleed off on its own and try again later */
status = MOVE_BUSY;
}
} else {
if (settings.verbose > 2) {
fprintf(stderr, "Slab reassign hit a busy item: refcount: %d (%d -> %d)\n",
it->refcount, slab_rebal.s_clsid, slab_rebal.d_clsid);
}
status = MOVE_BUSY;
}
/* Item lock must be held while modifying refcount */
if (status == MOVE_BUSY) {
refcount_decr(&it->refcount);
item_trylock_unlock(hold_lock);
}
}
} else {
/* See above comment. No ITEM_SLABBED or ITEM_LINKED. Mark
* busy and wait for item to complete its upload. */
status = MOVE_BUSY;
}
}
int save_item = 0;
item *new_it = NULL;
size_t ntotal = 0;
switch (status) {
case MOVE_FROM_LRU:
/* Lock order is LRU locks -> slabs_lock. unlink uses LRU lock.
* We only need to hold the slabs_lock while initially looking
* at an item, and at this point we have an exclusive refcount
* (2) + the item is locked. Drop slabs lock, drop item to
* refcount 1 (just our own, then fall through and wipe it
*/
/* Check if expired or flushed */
ntotal = ITEM_ntotal(it);
/* REQUIRES slabs_lock: CHECK FOR cls->sl_curr > 0 */
if (ch == NULL && (it->it_flags & ITEM_CHUNKED)) {
/* Chunked should be identical to non-chunked, except we need
* to swap out ntotal for the head-chunk-total. */
ntotal = s_cls->size;
}
if ((it->exptime != 0 && it->exptime < current_time)
|| item_is_flushed(it)) {
/* Expired, don't save. */
save_item = 0;
} else if (ch == NULL &&
(new_it = slab_rebalance_alloc(ntotal, slab_rebal.s_clsid)) == NULL) {
/* Not a chunk of an item, and nomem. */
save_item = 0;
slab_rebal.evictions_nomem++;
} else if (ch != NULL &&
(new_it = slab_rebalance_alloc(s_cls->size, slab_rebal.s_clsid)) == NULL) {
/* Is a chunk of an item, and nomem. */
save_item = 0;
slab_rebal.evictions_nomem++;
} else {
/* Was whatever it was, and we have memory for it. */
save_item = 1;
}
pthread_mutex_unlock(&slabs_lock);
unsigned int requested_adjust = 0;
if (save_item) {
if (ch == NULL) {
assert((new_it->it_flags & ITEM_CHUNKED) == 0);
/* if free memory, memcpy. clear prev/next/h_bucket */
memcpy(new_it, it, ntotal);
new_it->prev = 0;
new_it->next = 0;
new_it->h_next = 0;
/* These are definitely required. else fails assert */
new_it->it_flags &= ~ITEM_LINKED;
new_it->refcount = 0;
do_item_replace(it, new_it, hv);
/* Need to walk the chunks and repoint head */
if (new_it->it_flags & ITEM_CHUNKED) {
item_chunk *fch = (item_chunk *) ITEM_data(new_it);
fch->next->prev = fch;
while (fch) {
fch->head = new_it;
fch = fch->next;
}
}
it->refcount = 0;
it->it_flags = ITEM_SLABBED|ITEM_FETCHED;
#ifdef DEBUG_SLAB_MOVER
memcpy(ITEM_key(it), "deadbeef", 8);
#endif
slab_rebal.rescues++;
requested_adjust = ntotal;
} else {
item_chunk *nch = (item_chunk *) new_it;
/* Chunks always have head chunk (the main it) */
ch->prev->next = nch;
if (ch->next)
ch->next->prev = nch;
memcpy(nch, ch, ch->used + sizeof(item_chunk));
ch->refcount = 0;
ch->it_flags = ITEM_SLABBED|ITEM_FETCHED;
slab_rebal.chunk_rescues++;
#ifdef DEBUG_SLAB_MOVER
memcpy(ITEM_key((item *)ch), "deadbeef", 8);
#endif
refcount_decr(&it->refcount);
requested_adjust = s_cls->size;
}
} else {
/* restore ntotal in case we tried saving a head chunk. */
ntotal = ITEM_ntotal(it);
do_item_unlink(it, hv);
slabs_free(it, ntotal, slab_rebal.s_clsid);
/* Swing around again later to remove it from the freelist. */
slab_rebal.busy_items++;
was_busy++;
}
item_trylock_unlock(hold_lock);
pthread_mutex_lock(&slabs_lock);
/* Always remove the ntotal, as we added it in during
* do_slabs_alloc() when copying the item.
*/
s_cls->requested -= requested_adjust;
break;
case MOVE_FROM_SLAB:
it->refcount = 0;
it->it_flags = ITEM_SLABBED|ITEM_FETCHED;
#ifdef DEBUG_SLAB_MOVER
memcpy(ITEM_key(it), "deadbeef", 8);
#endif
break;
case MOVE_BUSY:
case MOVE_LOCKED:
slab_rebal.busy_items++;
was_busy++;
break;
case MOVE_PASS:
break;
}
slab_rebal.slab_pos = (char *)slab_rebal.slab_pos + s_cls->size;
if (slab_rebal.slab_pos >= slab_rebal.slab_end)
break;
}
if (slab_rebal.slab_pos >= slab_rebal.slab_end) {
/* Some items were busy, start again from the top */
if (slab_rebal.busy_items) {
slab_rebal.slab_pos = slab_rebal.slab_start;
STATS_LOCK();
stats.slab_reassign_busy_items += slab_rebal.busy_items;
STATS_UNLOCK();
slab_rebal.busy_items = 0;
} else {
slab_rebal.done++;
}
}
pthread_mutex_unlock(&slabs_lock);
return was_busy;
}
static void slab_rebalance_finish(void) {
slabclass_t *s_cls;
slabclass_t *d_cls;
int x;
uint32_t rescues;
uint32_t evictions_nomem;
uint32_t inline_reclaim;
uint32_t chunk_rescues;
pthread_mutex_lock(&slabs_lock);
s_cls = &slabclass[slab_rebal.s_clsid];
d_cls = &slabclass[slab_rebal.d_clsid];
#ifdef DEBUG_SLAB_MOVER
/* If the algorithm is broken, live items can sneak in. */
slab_rebal.slab_pos = slab_rebal.slab_start;
while (1) {
item *it = slab_rebal.slab_pos;
assert(it->it_flags == (ITEM_SLABBED|ITEM_FETCHED));
assert(memcmp(ITEM_key(it), "deadbeef", 8) == 0);
it->it_flags = ITEM_SLABBED|ITEM_FETCHED;
slab_rebal.slab_pos = (char *)slab_rebal.slab_pos + s_cls->size;
if (slab_rebal.slab_pos >= slab_rebal.slab_end)
break;
}
#endif
/* At this point the stolen slab is completely clear.
* We always kill the "first"/"oldest" slab page in the slab_list, so
* shuffle the page list backwards and decrement.
*/
s_cls->slabs--;
for (x = 0; x < s_cls->slabs; x++) {
s_cls->slab_list[x] = s_cls->slab_list[x+1];
}
d_cls->slab_list[d_cls->slabs++] = slab_rebal.slab_start;
/* Don't need to split the page into chunks if we're just storing it */
if (slab_rebal.d_clsid > SLAB_GLOBAL_PAGE_POOL) {
memset(slab_rebal.slab_start, 0, (size_t)settings.item_size_max);
split_slab_page_into_freelist(slab_rebal.slab_start,
slab_rebal.d_clsid);
} else if (slab_rebal.d_clsid == SLAB_GLOBAL_PAGE_POOL) {
/* mem_malloc'ed might be higher than mem_limit. */
memory_release();
}
slab_rebal.done = 0;
slab_rebal.s_clsid = 0;
slab_rebal.d_clsid = 0;
slab_rebal.slab_start = NULL;
slab_rebal.slab_end = NULL;
slab_rebal.slab_pos = NULL;
evictions_nomem = slab_rebal.evictions_nomem;
inline_reclaim = slab_rebal.inline_reclaim;
rescues = slab_rebal.rescues;
chunk_rescues = slab_rebal.chunk_rescues;
slab_rebal.evictions_nomem = 0;
slab_rebal.inline_reclaim = 0;
slab_rebal.rescues = 0;
slab_rebalance_signal = 0;
pthread_mutex_unlock(&slabs_lock);
STATS_LOCK();
stats.slabs_moved++;
stats.slab_reassign_rescues += rescues;
stats.slab_reassign_evictions_nomem += evictions_nomem;
stats.slab_reassign_inline_reclaim += inline_reclaim;
stats.slab_reassign_chunk_rescues += chunk_rescues;
stats_state.slab_reassign_running = false;
STATS_UNLOCK();
if (settings.verbose > 1) {
fprintf(stderr, "finished a slab move\n");
}
}
/* Slab mover thread.
* Sits waiting for a condition to jump off and shovel some memory about
*/
static void *slab_rebalance_thread(void *arg) {
int was_busy = 0;
/* So we first pass into cond_wait with the mutex held */
mutex_lock(&slabs_rebalance_lock);
while (do_run_slab_rebalance_thread) {
if (slab_rebalance_signal == 1) {
if (slab_rebalance_start() < 0) {
/* Handle errors with more specifity as required. */
slab_rebalance_signal = 0;
}
was_busy = 0;
} else if (slab_rebalance_signal && slab_rebal.slab_start != NULL) {
was_busy = slab_rebalance_move();
}
if (slab_rebal.done) {
slab_rebalance_finish();
} else if (was_busy) {
/* Stuck waiting for some items to unlock, so slow down a bit
* to give them a chance to free up */
usleep(50);
}
if (slab_rebalance_signal == 0) {
/* always hold this lock while we're running */
pthread_cond_wait(&slab_rebalance_cond, &slabs_rebalance_lock);
}
}
return NULL;
}
/* Iterate at most once through the slab classes and pick a "random" source.
* I like this better than calling rand() since rand() is slow enough that we
* can just check all of the classes once instead.
*/
static int slabs_reassign_pick_any(int dst) {
static int cur = POWER_SMALLEST - 1;
int tries = power_largest - POWER_SMALLEST + 1;
for (; tries > 0; tries--) {
cur++;
if (cur > power_largest)
cur = POWER_SMALLEST;
if (cur == dst)
continue;
if (slabclass[cur].slabs > 1) {
return cur;
}
}
return -1;
}
static enum reassign_result_type do_slabs_reassign(int src, int dst) {
if (slab_rebalance_signal != 0)
return REASSIGN_RUNNING;
if (src == dst)
return REASSIGN_SRC_DST_SAME;
/* Special indicator to choose ourselves. */
if (src == -1) {
src = slabs_reassign_pick_any(dst);
/* TODO: If we end up back at -1, return a new error type */
}
if (src < POWER_SMALLEST || src > power_largest ||
dst < SLAB_GLOBAL_PAGE_POOL || dst > power_largest)
return REASSIGN_BADCLASS;
if (slabclass[src].slabs < 2)
return REASSIGN_NOSPARE;
slab_rebal.s_clsid = src;
slab_rebal.d_clsid = dst;
slab_rebalance_signal = 1;
pthread_cond_signal(&slab_rebalance_cond);
return REASSIGN_OK;
}
enum reassign_result_type slabs_reassign(int src, int dst) {
enum reassign_result_type ret;
if (pthread_mutex_trylock(&slabs_rebalance_lock) != 0) {
return REASSIGN_RUNNING;
}
ret = do_slabs_reassign(src, dst);
pthread_mutex_unlock(&slabs_rebalance_lock);
return ret;
}
/* If we hold this lock, rebalancer can't wake up or move */
void slabs_rebalancer_pause(void) {
pthread_mutex_lock(&slabs_rebalance_lock);
}
void slabs_rebalancer_resume(void) {
pthread_mutex_unlock(&slabs_rebalance_lock);
}
static pthread_t rebalance_tid;
int start_slab_maintenance_thread(void) {
int ret;
slab_rebalance_signal = 0;
slab_rebal.slab_start = NULL;
char *env = getenv("MEMCACHED_SLAB_BULK_CHECK");
if (env != NULL) {
slab_bulk_check = atoi(env);
if (slab_bulk_check == 0) {
slab_bulk_check = DEFAULT_SLAB_BULK_CHECK;
}
}
if (pthread_cond_init(&slab_rebalance_cond, NULL) != 0) {
fprintf(stderr, "Can't intiialize rebalance condition\n");
return -1;
}
pthread_mutex_init(&slabs_rebalance_lock, NULL);
if ((ret = pthread_create(&rebalance_tid, NULL,
slab_rebalance_thread, NULL)) != 0) {
fprintf(stderr, "Can't create rebal thread: %s\n", strerror(ret));
return -1;
}
return 0;
}
/* The maintenance thread is on a sleep/loop cycle, so it should join after a
* short wait */
void stop_slab_maintenance_thread(void) {
mutex_lock(&slabs_rebalance_lock);
do_run_slab_thread = 0;
do_run_slab_rebalance_thread = 0;
pthread_cond_signal(&slab_rebalance_cond);
pthread_mutex_unlock(&slabs_rebalance_lock);
/* Wait for the maintenance thread to stop */
pthread_join(rebalance_tid, NULL);
}
