7dae142a2e
# Background The RDB file is usually generated and used once and seldom used again, but the content would reside in page cache until OS evicts it. A potential problem is that once the free memory exhausts, the OS have to reclaim some memory from page cache or swap anonymous page out, which may result in a jitters to the Redis service. Supposing an exact scenario, a high-capacity machine hosts many redis instances, and we're upgrading the Redis together. The page cache in host machine increases as RDBs are generated. Once the free memory drop into low watermark(which is more likely to happen in older Linux kernel like 3.10, before [watermark_scale_factor](https://lore.kernel.org/lkml/1455813719-2395-1-git-send-email-hannes@cmpxchg.org/) is introduced, the `low watermark` is linear to `min watermark`, and there'is not too much buffer space for `kswapd` to be wake up to reclaim memory), a `direct reclaim` happens, which means the process would stall to wait for memory allocation. # What the PR does The PR introduces a capability to reclaim the cache when the RDB is operated. Generally there're two cases, read and write the RDB. For read it's a little messy to address the incremental reclaim, so the reclaim is done in one go in background after the load is finished to avoid blocking the work thread. For write, incremental reclaim amortizes the work of reclaim so no need to put it into background, and the peak watermark of cache can be reduced in this way. Two cases are addresses specially, replication and restart, for both of which the cache is leveraged to speed up the processing, so the reclaim is postponed to a right time. To do this, a flag is added to`rdbSave` and `rdbLoad` to control whether the cache need to be kept, with the default value false. # Something deserve noting 1. Though `posix_fadvise` is the POSIX standard, but only few platform support it, e.g. Linux, FreeBSD 10.0. 2. In Linux `posix_fadvise` only take effect on writeback-ed pages, so a `sync`(or `fsync`, `fdatasync`) is needed to flush the dirty page before `posix_fadvise` if we reclaim write cache. # About test A unit test is added to verify the effect of `posix_fadvise`. In integration test overall cache increase is checked, as well as the cache backed by RDB as a specific TCL test is executed in isolated Github action job.
100 lines
4.3 KiB
C
100 lines
4.3 KiB
C
/*
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* Copyright (c) 2009-2012, Salvatore Sanfilippo <antirez at gmail dot com>
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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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#ifndef __REDIS_UTIL_H
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#define __REDIS_UTIL_H
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#include <stdint.h>
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#include "sds.h"
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/* The maximum number of characters needed to represent a long double
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* as a string (long double has a huge range of some 4952 chars, see LDBL_MAX).
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* This should be the size of the buffer given to ld2string */
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#define MAX_LONG_DOUBLE_CHARS 5*1024
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/* The maximum number of characters needed to represent a double
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* as a string (double has a huge range of some 328 chars, see DBL_MAX).
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* This should be the size of the buffer for sprintf with %f */
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#define MAX_DOUBLE_CHARS 400
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/* The maximum number of characters needed to for d2string/fpconv_dtoa call.
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* Since it uses %g and not %f, some 40 chars should be enough. */
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#define MAX_D2STRING_CHARS 128
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/* Bytes needed for long -> str + '\0' */
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#define LONG_STR_SIZE 21
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/* long double to string conversion options */
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typedef enum {
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LD_STR_AUTO, /* %.17Lg */
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LD_STR_HUMAN, /* %.17Lf + Trimming of trailing zeros */
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LD_STR_HEX /* %La */
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} ld2string_mode;
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int stringmatchlen(const char *p, int plen, const char *s, int slen, int nocase);
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int stringmatch(const char *p, const char *s, int nocase);
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int stringmatchlen_fuzz_test(void);
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unsigned long long memtoull(const char *p, int *err);
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const char *mempbrk(const char *s, size_t len, const char *chars, size_t charslen);
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char *memmapchars(char *s, size_t len, const char *from, const char *to, size_t setlen);
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uint32_t digits10(uint64_t v);
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uint32_t sdigits10(int64_t v);
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int ll2string(char *s, size_t len, long long value);
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int ull2string(char *s, size_t len, unsigned long long value);
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int string2ll(const char *s, size_t slen, long long *value);
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int string2ull(const char *s, unsigned long long *value);
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int string2l(const char *s, size_t slen, long *value);
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int string2ld(const char *s, size_t slen, long double *dp);
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int string2d(const char *s, size_t slen, double *dp);
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int trimDoubleString(char *buf, size_t len);
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int d2string(char *buf, size_t len, double value);
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int fixedpoint_d2string(char *dst, size_t dstlen, double dvalue, int fractional_digits);
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int ld2string(char *buf, size_t len, long double value, ld2string_mode mode);
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int double2ll(double d, long long *out);
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int yesnotoi(char *s);
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sds getAbsolutePath(char *filename);
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long getTimeZone(void);
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int pathIsBaseName(char *path);
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int dirCreateIfMissing(char *dname);
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int dirExists(char *dname);
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int dirRemove(char *dname);
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int fileExist(char *filename);
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sds makePath(char *path, char *filename);
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int fsyncFileDir(const char *filename);
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int reclaimFilePageCache(int fd, size_t offset, size_t length);
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size_t redis_strlcpy(char *dst, const char *src, size_t dsize);
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size_t redis_strlcat(char *dst, const char *src, size_t dsize);
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#ifdef REDIS_TEST
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int utilTest(int argc, char **argv, int flags);
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#endif
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#endif
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