Re: [PATCHv6 1/6] zram: introduce compressing backend abstraction

[Minchan Kim]

Hello Sergey,

Hmm, I seem to know why you took a mistake about adding Ccing Andrew
because ./get_maintainer.pl doesn't say about Andrew. So it's totally
not your fault. But I don't have public git tree for zram and Andrew
usually pick zram patches with my Acked-by into mmotm tree.
So if we follow such model, we need something for ./get_maintainer.pl
to say about Andrew. Otherwise, I need a public tree and pull request
periodically. I will discuss with Andrew what's perferred/best way.
Anyway, until done, pz, add Andrew.

On Fri, Feb 21, 2014 at 02:50:38PM +0300, Sergey Senozhatsky wrote:
> ZRAM performs direct LZO compression algorithm calls, making it the one and
> only option. 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 by means of get() and put() semantics 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_get() turns caller into exclusive user of a stream
> (holding stream mutex until zram put stream), and zcomp_strm_put() 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_get(comp)
> 	zcomp_compress(comp, zstrm, src, &dst_len)
> 	[..] /* copy compressed data */
> 	zcomp_strm_put(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@xxxxxxxxx>
> ---
>  drivers/block/zram/zcomp.c     | 116 +++++++++++++++++++++++++++++++++++++++++
>  drivers/block/zram/zcomp.h     |  53 +++++++++++++++++++
>  drivers/block/zram/zcomp_lzo.c |  48 +++++++++++++++++
>  3 files changed, 217 insertions(+)
>  create mode 100644 drivers/block/zram/zcomp.c
>  create mode 100644 drivers/block/zram/zcomp.h
>  create mode 100644 drivers/block/zram/zcomp_lzo.c
> 
> diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
> new file mode 100644
> index 0000000..db72f3d
> --- /dev/null
> +++ b/drivers/block/zram/zcomp.c
> @@ -0,0 +1,116 @@
> +/*
> + * Copyright (C) 2014 Sergey Senozhatsky.
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation; either version
> + * 2 of the License, or (at your option) any later version.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/string.h>
> +#include <linux/slab.h>
> +#include <linux/wait.h>
> +#include <linux/sched.h>
> +
> +#include "zcomp.h"
> +
> +extern struct zcomp_backend zcomp_lzo;
> +
> +static struct zcomp_backend *find_backend(const char *compress)
> +{
> +	if (strncmp(compress, "lzo", 3) == 0)
> +		return &zcomp_lzo;
> +	return NULL;
> +}
> +
> +static void zcomp_strm_free(struct zcomp *comp, struct zcomp_strm *zstrm)
> +{
> +	if (zstrm->private)
> +		comp->backend->destroy(zstrm->private);
> +	free_pages((unsigned long)zstrm->buffer, 1);
> +	kfree(zstrm);
> +}
> +
> +/*
> + * allocate new zcomp_strm structure with ->private initialized by
> + * backend, return NULL on error
> + */
> +static struct zcomp_strm *zcomp_strm_alloc(struct zcomp *comp)
> +{
> +	struct zcomp_strm *zstrm = kmalloc(sizeof(*zstrm), GFP_KERNEL);
> +	if (!zstrm)
> +		return NULL;
> +
> +	zstrm->private = comp->backend->create();
> +	/*
> +	 * allocate 2 pages. 1 for compressed data, plus 1 extra for the
> +	 * case when compressed size is larger than the original one
> +	 */
> +	zstrm->buffer = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, 1);
> +	if (!zstrm->private || !zstrm->buffer) {
> +		zcomp_strm_free(comp, zstrm);
> +		zstrm = NULL;
> +	}
> +	return zstrm;
> +}
> +
> +struct zcomp_strm *zcomp_strm_get(struct zcomp *comp)
> +{
> +	mutex_lock(&comp->strm_lock);
> +	return comp->zstrm;
> +}
> +
> +void zcomp_strm_put(struct zcomp *comp, struct zcomp_strm *zstrm)
> +{
> +	mutex_unlock(&comp->strm_lock);
> +}
> +
> +int zcomp_compress(struct zcomp *comp, struct zcomp_strm *zstrm,
> +		const unsigned char *src, size_t *dst_len)
> +{
> +	return comp->backend->compress(src, zstrm->buffer, dst_len,
> +			zstrm->private);
> +}
> +
> +int zcomp_decompress(struct zcomp *comp, const unsigned char *src,
> +		size_t src_len, unsigned char *dst)
> +{
> +	return comp->backend->decompress(src, src_len, dst);
> +}
> +
> +void zcomp_destroy(struct zcomp *comp)
> +{
> +	zcomp_strm_free(comp, comp->zstrm);
> +	kfree(comp);
> +}
> +
> +/*
> + * search available compressors for requested algorithm.
> + * allocate new zcomp and initialize it. return NULL
> + * if requested algorithm is not supported or in case
> + * of init error
> + */
> +struct zcomp *zcomp_create(const char *compress)
> +{
> +	struct zcomp *comp;
> +	struct zcomp_backend *backend;
> +
> +	backend = find_backend(compress);
> +	if (!backend)
> +		return NULL;
> +
> +	comp = kmalloc(sizeof(struct zcomp), GFP_KERNEL);
> +	if (!comp)
> +		return NULL;
> +
> +	comp->backend = backend;
> +	mutex_init(&comp->strm_lock);
> +
> +	comp->zstrm = zcomp_strm_alloc(comp);
> +	if (!comp->zstrm) {
> +		zcomp_destroy(comp);

Just use kfree instead of zcomp_destroy.
Pz, add my Acked-by in later version if you fix it.

Acked-by: Minchan Kim <minchan@xxxxxxxxxx>

-- 
Kind regards,
Minchan Kim
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