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redict/src/defrag.c

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active memory defragmentation
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/*
* Active memory defragmentation
* Try to find key / value allocations that need to be re-allocated in order
* to reduce external fragmentation.
* We do that by scanning the keyspace and for each pointer we have, we can try to
* ask the allocator if moving it to a new address will help reduce fragmentation.
*
* Copyright (c) 2017, Oran Agra
* Copyright (c) 2017, Redis Labs, Inc
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* * Neither the name of Redis nor the names of its contributors may be used
* to endorse or promote products derived from this software without
* specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#include "server.h"
#include <time.h>
#include <assert.h>
#include <stddef.h>
#if defined(USE_JEMALLOC) && defined(MALLOCX_TCACHE_NONE)
/* this method was added to jemalloc in order to help us understand which
* pointers are worthwhile moving and which aren't */
int je_get_defrag_hint(void* ptr, int *bin_util, int *run_util);
/* Defrag helper for generic allocations.
*
* returns NULL in case the allocatoin wasn't moved.
* when it returns a non-null value, the old pointer was already released
* and should NOT be accessed. */
void* activeDefragAlloc(void *ptr) {
int bin_util, run_util;
size_t size;
void *newptr;
if(!je_get_defrag_hint(ptr, &bin_util, &run_util)) {
server.stat_active_defrag_misses++;
return NULL;
}
/* if this run is more utilized than the average utilization in this bin (or it is full), skip it.
* this will eventually move all the allocations from relatively empty runs into relatively full runs. */
if (run_util > bin_util || run_util == 1<<16) {
server.stat_active_defrag_misses++;
return NULL;
}
/* move this allocation to a new allocation.
* make sure not to use the thread cache. so that we don't get back the same pointers we try to free */
size = zmalloc_size(ptr);
newptr = zmalloc_no_tcache(size);
memcpy(newptr, ptr, size);
zfree_no_tcache(ptr);
return newptr;
}
/*Defrag helper for sds strings
*
* returns NULL in case the allocatoin wasn't moved.
* when it returns a non-null value, the old pointer was already released
* and should NOT be accessed. */
sds activeDefragSds(sds sdsptr) {
void* ptr = sdsAllocPtr(sdsptr);
void* newptr = activeDefragAlloc(ptr);
if (newptr) {
size_t offset = sdsptr - (char*)ptr;
sdsptr = (char*)newptr + offset;
return sdsptr;
}
return NULL;
}
/* Defrag helper for robj and/or string objects
*
* returns NULL in case the allocatoin wasn't moved.
* when it returns a non-null value, the old pointer was already released
* and should NOT be accessed. */
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robj *activeDefragStringOb(robj* ob, int *defragged) {
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robj *ret = NULL;
if (ob->refcount!=1)
return NULL;
/* try to defrag robj (only if not an EMBSTR type (handled below) */
if (ob->type!=OBJ_STRING || ob->encoding!=OBJ_ENCODING_EMBSTR) {
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if ((ret = activeDefragAlloc(ob))) {
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ob = ret;
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(*defragged)++;
}
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}
/* try to defrag string object */
if (ob->type == OBJ_STRING) {
if(ob->encoding==OBJ_ENCODING_RAW) {
sds newsds = activeDefragSds((sds)ob->ptr);
if (newsds) {
ob->ptr = newsds;
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(*defragged)++;
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}
} else if (ob->encoding==OBJ_ENCODING_EMBSTR) {
/* the sds is embedded in the object allocation, calculate the offset and update the pointer in the new allocation */
long ofs = (intptr_t)ob->ptr - (intptr_t)ob;
if ((ret = activeDefragAlloc(ob))) {
ret->ptr = (void*)((intptr_t)ret + ofs);
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(*defragged)++;
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}
} else if (ob->encoding!=OBJ_ENCODING_INT) {
serverPanic("Unknown string encoding");
}
}
return ret;
}
/* Defrag helper for dictEntries to be used during dict iteration (called on each step).
* returns a stat of how many pointers were moved. */
int dictIterDefragEntry(dictIterator *iter) {
/* This function is a little bit dirty since it messes with the internals of the dict and it's iterator,
* but the benefit is that it is very easy to use, and require no other chagnes in the dict. */
int defragged = 0;
dictht *ht;
/* handle the next entry (if there is one), and update the pointer in the current entry. */
if (iter->nextEntry) {
dictEntry *newde = activeDefragAlloc(iter->nextEntry);
if (newde) {
defragged++;
iter->nextEntry = newde;
iter->entry->next = newde;
}
}
/* handle the case of the first entry in the hash bucket. */
ht = &iter->d->ht[iter->table];
if (ht->table[iter->index] == iter->entry) {
dictEntry *newde = activeDefragAlloc(iter->entry);
if (newde) {
iter->entry = newde;
ht->table[iter->index] = newde;
defragged++;
}
}
return defragged;
}
/* Defrag helper for dict main allocations (dict struct, and hash tables).
* receives a pointer to the dict* and implicitly updates it when the dict struct itself was moved.
* returns a stat of how many pointers were moved. */
int dictDefragTables(dict** dictRef) {
dict *d = *dictRef;
dictEntry **newtable;
int defragged = 0;
/* handle the dict struct */
dict *newd = activeDefragAlloc(d);
if (newd)
defragged++, *dictRef = d = newd;
/* handle the first hash table */
newtable = activeDefragAlloc(d->ht[0].table);
if (newtable)
defragged++, d->ht[0].table = newtable;
/* handle the second hash table */
if (d->ht[1].table) {
newtable = activeDefragAlloc(d->ht[1].table);
if (newtable)
defragged++, d->ht[1].table = newtable;
}
return defragged;
}
/* Internal function used by zslDefrag */
void zslUpdateNode(zskiplist *zsl, zskiplistNode *oldnode, zskiplistNode *newnode, zskiplistNode **update) {
int i;
for (i = 0; i < zsl->level; i++) {
if (update[i]->level[i].forward == oldnode)
update[i]->level[i].forward = newnode;
}
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serverAssert(zsl->header!=oldnode);
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if (newnode->level[0].forward) {
serverAssert(newnode->level[0].forward->backward==oldnode);
newnode->level[0].forward->backward = newnode;
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} else {
serverAssert(zsl->tail==oldnode);
zsl->tail = newnode;
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}
}
/* Defrag helper for sorted set.
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* Update the robj pointer, defrag the skiplist struct and return the new score reference.
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* we may not access oldele pointer (not even the pointer stored in the skiplist), as it was already freed.
* newele may be null, in which case we only need to defrag the skiplist, but not update the obj pointer.
* when return value is non-NULL, it is the score reference that must be updated in the dict record. */
double *zslDefrag(zskiplist *zsl, double score, sds oldele, sds newele) {
zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x, *newx;
int i;
sds ele = newele? newele: oldele;
/* find the skiplist node referring to the object that was moved,
* and all pointers that need to be updated if we'll end up moving the skiplist node. */
x = zsl->header;
for (i = zsl->level-1; i >= 0; i--) {
while (x->level[i].forward &&
x->level[i].forward->ele != oldele && /* make sure not to access the ->obj pointer if it matches oldele */
(x->level[i].forward->score < score ||
(x->level[i].forward->score == score &&
sdscmp(x->level[i].forward->ele,ele) < 0)))
x = x->level[i].forward;
update[i] = x;
}
/* update the robj pointer inside the skip list record. */
x = x->level[0].forward;
serverAssert(x && score == x->score && x->ele==oldele);
if (newele)
x->ele = newele;
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/* try to defrag the skiplist record itself */
newx = activeDefragAlloc(x);
if (newx) {
zslUpdateNode(zsl, x, newx, update);
return &newx->score;
}
return NULL;
}
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/* Utility function that replaces an old key pointer in the dictionary with a new pointer.
* Additionally, we try to defrag the dictEntry in that dict.
* oldkey mey be a dead pointer and should not be accessed (we get a pre-calculated hash value).
* newkey may be null if the key pointer wasn't moved.
* return value is the the dictEntry if found, or NULL if not found.
* NOTE: this is very ugly code, but it let's us avoid the complication of doing a scan on another dict. */
dictEntry* replaceSateliteDictKeyPtrAndOrDifragDictEntry(dict *d, sds oldkey, sds newkey, unsigned int hash, int *defragged) {
dictEntry **deref = dictFindEntryRefByPtrAndHash(d, oldkey, hash);
if (deref) {
dictEntry *de = *deref;
dictEntry *newde = activeDefragAlloc(de);
if (newde) {
de = *deref = newde;
(*defragged)++;
}
if (newkey)
de->key = newkey;
return de;
}
return NULL;
}
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/* for each key we scan in the main dict, this function will attempt to defrag all the various pointers it has.
* returns a stat of how many pointers were moved. */
int defargKey(redisDb *db, dictEntry *de) {
sds keysds = dictGetKey(de);
robj *newob, *ob;
unsigned char *newzl;
dict *d;
dictIterator *di;
int defragged = 0;
sds newsds;
/* try to defrag the key name */
newsds = activeDefragSds(keysds);
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if (newsds)
defragged++, de->key = newsds;
if (dictSize(db->expires)) {
/* Dirty code:
* i can't search in db->expires for that key after i already released the pointer it holds
* it won't be able to do the string compare */
unsigned int hash = dictGetHash(db->dict, de->key);
replaceSateliteDictKeyPtrAndOrDifragDictEntry(db->expires, keysds, newsds, hash, &defragged);
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}
/* try to defrag robj and / or string value */
ob = dictGetVal(de);
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if ((newob = activeDefragStringOb(ob, &defragged))) {
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de->v.val = newob;
ob = newob;
}
if (ob->type == OBJ_STRING) {
/* already handled in activeDefragStringOb */
} else if (ob->type == OBJ_LIST) {
if (ob->encoding == OBJ_ENCODING_QUICKLIST) {
quicklist *ql = ob->ptr, *newql;
quicklistNode *node = ql->head, *newnode;
if ((newql = activeDefragAlloc(ql)))
defragged++, ob->ptr = ql = newql;
do {
if ((newnode = activeDefragAlloc(node))) {
if (newnode->prev)
newnode->prev->next = newnode;
else
ql->head = newnode;
if (newnode->next)
newnode->next->prev = newnode;
else
ql->tail = newnode;
node = newnode;
defragged++;
}
if ((newzl = activeDefragAlloc(node->zl)))
defragged++, node->zl = newzl;
} while ((node = node->next));
} else if (ob->encoding == OBJ_ENCODING_ZIPLIST) {
if ((newzl = activeDefragAlloc(ob->ptr)))
defragged++, ob->ptr = newzl;
} else {
serverPanic("Unknown list encoding");
}
} else if (ob->type == OBJ_SET) {
if (ob->encoding == OBJ_ENCODING_HT) {
d = ob->ptr;
di = dictGetIterator(d);
while((de = dictNext(di)) != NULL) {
sds sdsele = dictGetKey(de);
if ((newsds = activeDefragSds(sdsele)))
defragged++, de->key = newsds;
defragged += dictIterDefragEntry(di);
}
dictReleaseIterator(di);
dictDefragTables((dict**)&ob->ptr);
} else if (ob->encoding == OBJ_ENCODING_INTSET) {
intset *is = ob->ptr;
intset *newis = activeDefragAlloc(is);
if (newis)
defragged++, ob->ptr = newis;
} else {
serverPanic("Unknown set encoding");
}
} else if (ob->type == OBJ_ZSET) {
if (ob->encoding == OBJ_ENCODING_ZIPLIST) {
if ((newzl = activeDefragAlloc(ob->ptr)))
defragged++, ob->ptr = newzl;
} else if (ob->encoding == OBJ_ENCODING_SKIPLIST) {
zset *zs = (zset*)ob->ptr;
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zset *newzs;
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zskiplist *newzsl;
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struct zskiplistNode *newheader;
if ((newzs = activeDefragAlloc(zs)))
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defragged++, ob->ptr = zs = newzs;
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if ((newzsl = activeDefragAlloc(zs->zsl)))
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defragged++, zs->zsl = newzsl;
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if ((newheader = activeDefragAlloc(zs->zsl->header)))
defragged++, zs->zsl->header = newheader;
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d = zs->dict;
di = dictGetIterator(d);
while((de = dictNext(di)) != NULL) {
double* newscore;
sds sdsele = dictGetKey(de);
if ((newsds = activeDefragSds(sdsele)))
defragged++, de->key = newsds;
newscore = zslDefrag(zs->zsl, *(double*)dictGetVal(de), sdsele, newsds);
if (newscore) {
dictSetVal(d, de, newscore);
defragged++;
}
defragged += dictIterDefragEntry(di);
}
dictReleaseIterator(di);
dictDefragTables(&zs->dict);
} else {
serverPanic("Unknown sorted set encoding");
}
} else if (ob->type == OBJ_HASH) {
if (ob->encoding == OBJ_ENCODING_ZIPLIST) {
if ((newzl = activeDefragAlloc(ob->ptr)))
defragged++, ob->ptr = newzl;
} else if (ob->encoding == OBJ_ENCODING_HT) {
d = ob->ptr;
di = dictGetIterator(d);
while((de = dictNext(di)) != NULL) {
sds sdsele = dictGetKey(de);
if ((newsds = activeDefragSds(sdsele)))
defragged++, de->key = newsds;
sdsele = dictGetVal(de);
if ((newsds = activeDefragSds(sdsele)))
defragged++, de->v.val = newsds;
defragged += dictIterDefragEntry(di);
}
dictReleaseIterator(di);
dictDefragTables((dict**)&ob->ptr);
} else {
serverPanic("Unknown hash encoding");
}
} else {
serverPanic("Unknown object type");
}
return defragged;
}
/* defrag scan callback for the main db dictionary */
void defragScanCallback(void *privdata, const dictEntry *de) {
int defragged = defargKey((redisDb*)privdata, (dictEntry*)de);
server.stat_active_defrag_hits += defragged;
if(defragged)
server.stat_active_defrag_key_hits++;
else
server.stat_active_defrag_key_misses++;
}
/* defrag scan callback for for each hash table bicket,
* used in order to defrag the dictEntry allocations */
void defragDictBucketCallback(void *privdata, dictEntry **bucketref) {
UNUSED(privdata);
while(*bucketref) {
dictEntry *de = *bucketref, *newde;
if ((newde = activeDefragAlloc(de))) {
*bucketref = newde;
}
bucketref = &(*bucketref)->next;
}
}
/* Utility function to get the fragmentation ratio from jemalloc.
* it is critical to do that by comparing only heap maps that belown to jemalloc, and skip ones the jemalloc keeps as spare.
* since we use this fragmentation ratio in order to decide if a defrag action should be taken or not,
* a false detection can cause the defragmenter to waste a lot of CPU without the possibility of getting any results. */
float getAllocatorFragmentation(size_t *out_frag_bytes) {
size_t epoch = 1, allocated = 0, resident = 0, active = 0, sz = sizeof(size_t);
je_mallctl("epoch", &epoch, &sz, &epoch, sz); /* Update the statistics cached by mallctl. */
je_mallctl("stats.resident", &resident, &sz, NULL, 0); /* unlike RSS, this does not include RSS from shared libraries and other non heap mappings */
je_mallctl("stats.active", &active, &sz, NULL, 0); /* unlike resident, this doesn't not include the pages jemalloc reserves for re-use (purge will clean that) */
je_mallctl("stats.allocated", &allocated, &sz, NULL, 0); /* unlike zmalloc_used_memory, this matches the stats.resident by taking into account all allocations done by this process (not only zmalloc) */
float frag_pct = ((float)active / allocated)*100 - 100;
size_t frag_bytes = active - allocated;
float rss_pct = ((float)resident / allocated)*100 - 100;
size_t rss_bytes = resident - allocated;
if(out_frag_bytes)
*out_frag_bytes = frag_bytes;
serverLog(LL_DEBUG,
"allocated=%zu, active=%zu, resident=%zu, frag=%.0f%% (%.0f%% rss), frag_bytes=%zu (%zu%% rss)",
allocated, active, resident, frag_pct, rss_pct, frag_bytes, rss_bytes);
return frag_pct;
}
#define INTERPOLATE(x, x1, x2, y1, y2) ( (y1) + ((x)-(x1)) * ((y2)-(y1)) / ((x2)-(x1)) )
#define LIMIT(y, min, max) ((y)<(min)? min: ((y)>(max)? max: (y)))
/* Perform incremental defragmentation work from the serverCron.
* This works in a similar way to activeExpireCycle, in the sense that
* we do incremental work across calls. */
void activeDefragCycle(void) {
static int current_db = -1;
static unsigned long cursor = 0;
static redisDb *db = NULL;
static long long start_scan, start_stat;
unsigned int iterations = 0;
unsigned long long defragged = server.stat_active_defrag_hits;
long long start, timelimit;
if (server.aof_child_pid!=-1 || server.rdb_child_pid!=-1)
return; /* defragging memory while there's a fork will just do damage. */
/* once a second, check if we the fragmentation justfies starting a scan or making it more aggressive */
run_with_period(1000) {
size_t frag_bytes;
float frag_pct = getAllocatorFragmentation(&frag_bytes);
/* if we're not already running, and below the threshold, exit. */
if (!server.active_defrag_running) {
if(frag_pct < server.active_defrag_threshold_lower || frag_bytes < server.active_defrag_ignore_bytes)
return;
}
/* calculate the adaptive aggressiveness of the defrag */
int cpu_pct = INTERPOLATE(frag_pct, server.active_defrag_threshold_lower, server.active_defrag_threshold_upper,
server.active_defrag_cycle_min, server.active_defrag_cycle_max);
cpu_pct = LIMIT(cpu_pct, server.active_defrag_cycle_min, server.active_defrag_cycle_max);
/* we allow increasing the aggressiveness during a scan, but don't reduce it */
if (!server.active_defrag_running || cpu_pct > server.active_defrag_running) {
server.active_defrag_running = cpu_pct;
serverLog(LL_VERBOSE,
"Starting active defrag, frag=%.0f%%, frag_bytes=%zu, cpu=%d%%",
frag_pct, frag_bytes, cpu_pct);
}
}
if (!server.active_defrag_running)
return;
/* See activeExpireCycle for how timelimit is handled. */
start = ustime();
timelimit = 1000000*server.active_defrag_running/server.hz/100;
if (timelimit <= 0) timelimit = 1;
do {
if (!cursor) {
/* Move on to next database, and stop if we reached the last one */
if (++current_db >= server.dbnum) {
long long now = ustime();
size_t frag_bytes;
float frag_pct = getAllocatorFragmentation(&frag_bytes);
serverLog(LL_VERBOSE,
"Active defrag done in %dms, reallocated=%d, frag=%.0f%%, frag_bytes=%zu",
(int)((now - start_scan)/1000), (int)(server.stat_active_defrag_hits - start_stat), frag_pct, frag_bytes);
start_scan = now;
current_db = -1;
cursor = 0;
db = NULL;
server.active_defrag_running = 0;
return;
}
else if (current_db==0) {
/* start a scan from the first database */
start_scan = ustime();
start_stat = server.stat_active_defrag_hits;
}
db = &server.db[current_db];
cursor = 0;
}
do {
cursor = dictScan(db->dict, cursor, defragScanCallback, defragDictBucketCallback, db);
/* once in 16 scan iterations, or 1000 pointer reallocations (if we have a lot of pointers in one hash bucket),
* check if we reached the tiem limit */
if (cursor && (++iterations > 16 || server.stat_active_defrag_hits - defragged > 1000)) {
if ((ustime() - start) > timelimit) {
return;
}
iterations = 0;
defragged = server.stat_active_defrag_hits;
}
} while(cursor);
} while(1);
}
#else /* USE_JEMALLOC */
void activeDefragCycle(void) {
/* not implemented yet*/
}
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#endif
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