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active memory defragmentation
This commit is contained in:
oranagra
antirez
527
src/defrag.c
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527
src/defrag.c
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@ -0,0 +1,527 @@
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/*
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* Active memory defragmentation
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* Try to find key / value allocations that need to be re-allocated in order
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* to reduce external fragmentation.
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* We do that by scanning the keyspace and for each pointer we have, we can try to
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* ask the allocator if moving it to a new address will help reduce fragmentation.
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*
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* Copyright (c) 2017, Oran Agra
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* Copyright (c) 2017, Redis Labs, Inc
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* * Redistributions of source code must retain the above copyright notice,
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* this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* * Neither the name of Redis nor the names of its contributors may be used
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* to endorse or promote products derived from this software without
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* specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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#include "server.h"
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#include <time.h>
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#include <assert.h>
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#include <stddef.h>
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#if defined(USE_JEMALLOC) && defined(MALLOCX_TCACHE_NONE)
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/* this method was added to jemalloc in order to help us understand which
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* pointers are worthwhile moving and which aren't */
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int je_get_defrag_hint(void* ptr, int *bin_util, int *run_util);
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/* Defrag helper for generic allocations.
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*
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* returns NULL in case the allocatoin wasn't moved.
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* when it returns a non-null value, the old pointer was already released
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* and should NOT be accessed. */
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void* activeDefragAlloc(void *ptr) {
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int bin_util, run_util;
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size_t size;
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void *newptr;
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if(!je_get_defrag_hint(ptr, &bin_util, &run_util)) {
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server.stat_active_defrag_misses++;
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return NULL;
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}
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/* if this run is more utilized than the average utilization in this bin (or it is full), skip it.
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* this will eventually move all the allocations from relatively empty runs into relatively full runs. */
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if (run_util > bin_util || run_util == 1<<16) {
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server.stat_active_defrag_misses++;
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return NULL;
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}
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/* move this allocation to a new allocation.
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* make sure not to use the thread cache. so that we don't get back the same pointers we try to free */
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size = zmalloc_size(ptr);
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newptr = zmalloc_no_tcache(size);
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memcpy(newptr, ptr, size);
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zfree_no_tcache(ptr);
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return newptr;
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}
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/*Defrag helper for sds strings
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*
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* returns NULL in case the allocatoin wasn't moved.
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* when it returns a non-null value, the old pointer was already released
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* and should NOT be accessed. */
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sds activeDefragSds(sds sdsptr) {
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void* ptr = sdsAllocPtr(sdsptr);
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void* newptr = activeDefragAlloc(ptr);
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if (newptr) {
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size_t offset = sdsptr - (char*)ptr;
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sdsptr = (char*)newptr + offset;
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return sdsptr;
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}
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return NULL;
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}
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/* Defrag helper for robj and/or string objects
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*
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* returns NULL in case the allocatoin wasn't moved.
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* when it returns a non-null value, the old pointer was already released
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* and should NOT be accessed. */
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robj *activeDefragStringOb(robj* ob) {
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robj *ret = NULL;
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if (ob->refcount!=1)
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return NULL;
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/* try to defrag robj (only if not an EMBSTR type (handled below) */
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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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}
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/* try to defrag string object */
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if (ob->type == OBJ_STRING) {
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if(ob->encoding==OBJ_ENCODING_RAW) {
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sds newsds = activeDefragSds((sds)ob->ptr);
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if (newsds) {
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ob->ptr = newsds;
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/* we don't need to change the return value here.
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* we can return NULL if 'ret' is still NULL (since the object pointer itself wasn't changed).
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* but we set return value to ob as an indication that we defragged a pointer (for stats).
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* NOTE: if ret is already set and the robj was moved, then our stats will be a bit off
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* since two pointers were moved, but we show only one in the stats */
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ret = ob;
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}
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} else if (ob->encoding==OBJ_ENCODING_EMBSTR) {
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/* the sds is embedded in the object allocation, calculate the offset and update the pointer in the new allocation */
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long ofs = (intptr_t)ob->ptr - (intptr_t)ob;
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if ((ret = activeDefragAlloc(ob))) {
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ret->ptr = (void*)((intptr_t)ret + ofs);
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}
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} else if (ob->encoding!=OBJ_ENCODING_INT) {
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serverPanic("Unknown string encoding");
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}
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}
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return ret;
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}
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/* Defrag helper for dictEntries to be used during dict iteration (called on each step).
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* returns a stat of how many pointers were moved. */
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int dictIterDefragEntry(dictIterator *iter) {
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/* This function is a little bit dirty since it messes with the internals of the dict and it's iterator,
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* but the benefit is that it is very easy to use, and require no other chagnes in the dict. */
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int defragged = 0;
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dictht *ht;
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/* handle the next entry (if there is one), and update the pointer in the current entry. */
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if (iter->nextEntry) {
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dictEntry *newde = activeDefragAlloc(iter->nextEntry);
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if (newde) {
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defragged++;
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iter->nextEntry = newde;
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iter->entry->next = newde;
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}
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}
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/* handle the case of the first entry in the hash bucket. */
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ht = &iter->d->ht[iter->table];
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if (ht->table[iter->index] == iter->entry) {
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dictEntry *newde = activeDefragAlloc(iter->entry);
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if (newde) {
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iter->entry = newde;
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ht->table[iter->index] = newde;
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defragged++;
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}
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}
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return defragged;
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}
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/* Defrag helper for dict main allocations (dict struct, and hash tables).
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* receives a pointer to the dict* and implicitly updates it when the dict struct itself was moved.
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* returns a stat of how many pointers were moved. */
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int dictDefragTables(dict** dictRef) {
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dict *d = *dictRef;
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dictEntry **newtable;
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int defragged = 0;
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/* handle the dict struct */
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dict *newd = activeDefragAlloc(d);
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if (newd)
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defragged++, *dictRef = d = newd;
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/* handle the first hash table */
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newtable = activeDefragAlloc(d->ht[0].table);
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if (newtable)
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defragged++, d->ht[0].table = newtable;
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/* handle the second hash table */
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if (d->ht[1].table) {
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newtable = activeDefragAlloc(d->ht[1].table);
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if (newtable)
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defragged++, d->ht[1].table = newtable;
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}
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return defragged;
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}
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/* Internal function used by zslDefrag */
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void zslUpdateNode(zskiplist *zsl, zskiplistNode *oldnode, zskiplistNode *newnode, zskiplistNode **update) {
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int i;
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for (i = 0; i < zsl->level; i++) {
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if (update[i]->level[i].forward == oldnode)
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update[i]->level[i].forward = newnode;
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}
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if (zsl->header==oldnode)
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zsl->header = newnode;
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if (zsl->tail==oldnode)
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zsl->tail = newnode;
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if (newnode->level[0].forward) {
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serverAssert(newnode->level[0].forward->backward==oldnode);
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newnode->level[0].forward->backward = newnode;
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}
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}
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/* Defrag helper for sorted set.
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* Update the robj pointer, defrag the 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.
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* newele may be null, in which case we only need to defrag the skiplist, but not update the obj pointer.
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* when return value is non-NULL, it is the score reference that must be updated in the dict record. */
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double *zslDefrag(zskiplist *zsl, double score, sds oldele, sds newele) {
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zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x, *newx;
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int i;
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sds ele = newele? newele: oldele;
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/* find the skiplist node referring to the object that was moved,
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* and all pointers that need to be updated if we'll end up moving the skiplist node. */
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x = zsl->header;
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for (i = zsl->level-1; i >= 0; i--) {
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while (x->level[i].forward &&
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x->level[i].forward->ele != oldele && /* make sure not to access the ->obj pointer if it matches oldele */
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(x->level[i].forward->score < score ||
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(x->level[i].forward->score == score &&
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sdscmp(x->level[i].forward->ele,ele) < 0)))
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x = x->level[i].forward;
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update[i] = x;
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}
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/* update the robj pointer inside the skip list record. */
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x = x->level[0].forward;
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serverAssert(x && score == x->score && x->ele==oldele);
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if (newele)
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x->ele = newele;
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/* try to defrag the skiplist record itself */
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newx = activeDefragAlloc(x);
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if (newx) {
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zslUpdateNode(zsl, x, newx, update);
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return &newx->score;
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}
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return NULL;
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}
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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.
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* returns a stat of how many pointers were moved. */
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int defargKey(redisDb *db, dictEntry *de) {
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sds keysds = dictGetKey(de);
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robj *newob, *ob;
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unsigned char *newzl;
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dict *d;
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dictIterator *di;
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int defragged = 0;
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sds newsds;
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/* try to defrag the key name */
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newsds = activeDefragSds(keysds);
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if (newsds) {
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de->key = newsds;
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if (dictSize(db->expires)) {
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/* Dirty code:
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* i can't search in db->expires for that key after i already released the pointer it holds
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* it won't be able to do the string compare */
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unsigned int hash = dictGetHash(db->dict, newsds);
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dictReplaceKeyPtr(db->expires, keysds, newsds, hash);
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}
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defragged++;
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}
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/* try to defrag robj and / or string value */
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ob = dictGetVal(de);
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if ((newob = activeDefragStringOb(ob))) {
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de->v.val = newob;
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ob = newob;
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defragged++;
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}
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if (ob->type == OBJ_STRING) {
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/* already handled in activeDefragStringOb */
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} else if (ob->type == OBJ_LIST) {
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if (ob->encoding == OBJ_ENCODING_QUICKLIST) {
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quicklist *ql = ob->ptr, *newql;
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quicklistNode *node = ql->head, *newnode;
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if ((newql = activeDefragAlloc(ql)))
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defragged++, ob->ptr = ql = newql;
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do {
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if ((newnode = activeDefragAlloc(node))) {
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if (newnode->prev)
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newnode->prev->next = newnode;
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else
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ql->head = newnode;
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if (newnode->next)
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newnode->next->prev = newnode;
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else
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ql->tail = newnode;
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node = newnode;
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defragged++;
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}
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if ((newzl = activeDefragAlloc(node->zl)))
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defragged++, node->zl = newzl;
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} while ((node = node->next));
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} else if (ob->encoding == OBJ_ENCODING_ZIPLIST) {
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if ((newzl = activeDefragAlloc(ob->ptr)))
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defragged++, ob->ptr = newzl;
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} else {
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serverPanic("Unknown list encoding");
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}
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} else if (ob->type == OBJ_SET) {
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if (ob->encoding == OBJ_ENCODING_HT) {
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d = ob->ptr;
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di = dictGetIterator(d);
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while((de = dictNext(di)) != NULL) {
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sds sdsele = dictGetKey(de);
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if ((newsds = activeDefragSds(sdsele)))
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defragged++, de->key = newsds;
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defragged += dictIterDefragEntry(di);
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}
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dictReleaseIterator(di);
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dictDefragTables((dict**)&ob->ptr);
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} else if (ob->encoding == OBJ_ENCODING_INTSET) {
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intset *is = ob->ptr;
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intset *newis = activeDefragAlloc(is);
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if (newis)
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defragged++, ob->ptr = newis;
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} else {
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serverPanic("Unknown set encoding");
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}
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} else if (ob->type == OBJ_ZSET) {
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if (ob->encoding == OBJ_ENCODING_ZIPLIST) {
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if ((newzl = activeDefragAlloc(ob->ptr)))
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defragged++, ob->ptr = newzl;
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} else if (ob->encoding == OBJ_ENCODING_SKIPLIST) {
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zset *zs = (zset*)ob->ptr;
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zset *newzs = activeDefragAlloc(zs);
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zskiplist *newzsl;
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if (newzs)
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defragged++, ob->ptr = zs = newzs;
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newzsl = activeDefragAlloc(zs->zsl);
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if (newzsl)
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defragged++, zs->zsl = newzsl;
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d = zs->dict;
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di = dictGetIterator(d);
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while((de = dictNext(di)) != NULL) {
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double* newscore;
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sds sdsele = dictGetKey(de);
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if ((newsds = activeDefragSds(sdsele)))
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defragged++, de->key = newsds;
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newscore = zslDefrag(zs->zsl, *(double*)dictGetVal(de), sdsele, newsds);
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if (newscore) {
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dictSetVal(d, de, newscore);
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defragged++;
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}
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defragged += dictIterDefragEntry(di);
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}
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dictReleaseIterator(di);
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dictDefragTables(&zs->dict);
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} else {
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serverPanic("Unknown sorted set encoding");
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}
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} else if (ob->type == OBJ_HASH) {
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if (ob->encoding == OBJ_ENCODING_ZIPLIST) {
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if ((newzl = activeDefragAlloc(ob->ptr)))
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defragged++, ob->ptr = newzl;
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} else if (ob->encoding == OBJ_ENCODING_HT) {
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d = ob->ptr;
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di = dictGetIterator(d);
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while((de = dictNext(di)) != NULL) {
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sds sdsele = dictGetKey(de);
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if ((newsds = activeDefragSds(sdsele)))
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defragged++, de->key = newsds;
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sdsele = dictGetVal(de);
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if ((newsds = activeDefragSds(sdsele)))
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defragged++, de->v.val = newsds;
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defragged += dictIterDefragEntry(di);
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}
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dictReleaseIterator(di);
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dictDefragTables((dict**)&ob->ptr);
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} else {
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serverPanic("Unknown hash encoding");
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}
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} else {
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serverPanic("Unknown object type");
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}
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return defragged;
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}
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||||
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/* defrag scan callback for the main db dictionary */
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void defragScanCallback(void *privdata, const dictEntry *de) {
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/* TODO: defrag the dictEntry (and also the entriy in expire dict). */
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int defragged = defargKey((redisDb*)privdata, (dictEntry*)de);
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server.stat_active_defrag_hits += defragged;
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if(defragged)
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server.stat_active_defrag_key_hits++;
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else
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server.stat_active_defrag_key_misses++;
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}
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||||
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||||
/* defrag scan callback for for each hash table bicket,
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* used in order to defrag the dictEntry allocations */
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||||
void defragDictBucketCallback(void *privdata, dictEntry **bucketref) {
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UNUSED(privdata);
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||||
while(*bucketref) {
|
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dictEntry *de = *bucketref, *newde;
|
||||
if ((newde = activeDefragAlloc(de))) {
|
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*bucketref = newde;
|
||||
}
|
||||
bucketref = &(*bucketref)->next;
|
||||
}
|
||||
}
|
||||
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||||
/* 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. */
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||||
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*/
|
||||
}
|
||||
|
||||
#endif
|
||||
Reference in New Issue
Block a user