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ZRAM performs direct LZO compression algorithm calls, making it the one and only option. While LZO is generally performs well, LZ4 algorithm tends to have a faster decompression (see http://code.google.com/p/lz4/ for full report) Name Ratio C.speed D.speed MB/s MB/s LZ4 (r101) 2.084 422 1820 LZO 2.06 2.106 414 600 Thus, users who have mostly read (decompress) usage scenarious or mixed workflow (writes with relatively high read ops number) will benefit from using LZ4 compression backend. Introduce compressing backend abstraction zcomp in order to support multiple compression algorithms with the following set of operations: .create .destroy .compress .decompress Schematically zram write() usually contains the following steps: 0) preparation (decompression of partioal IO, etc.) 1) lock buffer_lock mutex (protects meta compress buffers) 2) compress (using meta compress buffers) 3) alloc and map zs_pool object 4) copy compressed data (from meta compress buffers) to object allocated by 3) 5) free previous pool page, assign a new one 6) unlock buffer_lock mutex As we can see, compressing buffers must remain untouched from 1) to 4), because, otherwise, concurrent write() can overwrite data. At the same time, zram_meta must be aware of a) specific compression algorithm memory requirements and b) necessary locking to protect compression buffers. To remove requirement a) new struct zcomp_strm introduced, which contains a compress/decompress `buffer' and compression algorithm `private' part. While struct zcomp implements zcomp_strm stream handling and locking and removes requirement b) from zram meta. zcomp ->create() and ->destroy(), respectively, allocate and deallocate algorithm specific zcomp_strm `private' part. Every zcomp has zcomp stream and mutex to protect its compression stream. Stream usage semantics remains the same -- only one write can hold stream lock and use its buffers. zcomp_strm_find() turns caller into exclusive user of a stream (holding stream mutex until zram release stream), and zcomp_strm_release() makes zcomp stream available (unlock the stream mutex). Hence no concurrent write (compression) operations possible at the moment. iozone -t 3 -R -r 16K -s 60M -I +Z test base patched -------------------------------------------------- Initial write 597992.91 591660.58 Rewrite 609674.34 616054.97 Read 2404771.75 2452909.12 Re-read 2459216.81 2470074.44 Reverse Read 1652769.66 1589128.66 Stride read 2202441.81 2202173.31 Random read 2236311.47 2276565.31 Mixed workload 1423760.41 1709760.06 Random write 579584.08 615933.86 Pwrite 597550.02 594933.70 Pread 1703672.53 1718126.72 Fwrite 1330497.06 1461054.00 Fread 3922851.00 3957242.62 Usage examples: comp = zcomp_create(NAME) /* NAME e.g. "lzo" */ which initialises compressing backend if requested algorithm is supported. Compress: zstrm = zcomp_strm_find(comp) zcomp_compress(comp, zstrm, src, &dst_len) [..] /* copy compressed data */ zcomp_strm_release(comp, zstrm) Decompress: zcomp_decompress(comp, src, src_len, dst); Free compessing backend and its zcomp stream: zcomp_destroy(comp) Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: Nitin Gupta <ngupta@vflare.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
59 lines
1.5 KiB
C
59 lines
1.5 KiB
C
/*
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* Copyright (C) 2014 Sergey Senozhatsky.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#ifndef _ZCOMP_H_
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#define _ZCOMP_H_
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#include <linux/mutex.h>
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struct zcomp_strm {
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/* compression/decompression buffer */
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void *buffer;
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/*
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* The private data of the compression stream, only compression
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* stream backend can touch this (e.g. compression algorithm
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* working memory)
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*/
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void *private;
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};
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/* static compression backend */
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struct zcomp_backend {
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int (*compress)(const unsigned char *src, unsigned char *dst,
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size_t *dst_len, void *private);
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int (*decompress)(const unsigned char *src, size_t src_len,
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unsigned char *dst);
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void *(*create)(void);
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void (*destroy)(void *private);
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const char *name;
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};
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/* dynamic per-device compression frontend */
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struct zcomp {
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struct mutex strm_lock;
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struct zcomp_strm *zstrm;
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struct zcomp_backend *backend;
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};
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struct zcomp *zcomp_create(const char *comp);
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void zcomp_destroy(struct zcomp *comp);
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struct zcomp_strm *zcomp_strm_find(struct zcomp *comp);
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void zcomp_strm_release(struct zcomp *comp, struct zcomp_strm *zstrm);
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int zcomp_compress(struct zcomp *comp, struct zcomp_strm *zstrm,
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const unsigned char *src, size_t *dst_len);
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int zcomp_decompress(struct zcomp *comp, const unsigned char *src,
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size_t src_len, unsigned char *dst);
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#endif /* _ZCOMP_H_ */
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