Re: [PATCHv5 1/4] zram: introduce compressing backend abstraction

[Sergey Senozhatsky]

Hello,

On (02/18/14 05:10), Minchan Kim wrote:
> On Thu, Feb 13, 2014 at 08:43:19PM +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. Besides, zram holds buffer_lock almost through the whole write()
> > function, making parallel compression impossible. To remove requirement
> > a) new struct zcomp_strm introduced, which contain 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 a list of idle zcomp_strm structs, spinlock to protect idle
> > list and wait queue, making it possible to perform parallel compressions.
> > Each time zram issues a zcomp_strm_get() call, the following set of operations
> > performed:
> > - spin lock strm_lock
> > - if idle list is not empty, remove zcomp_strm from idle list, spin
> >   unlock and return zcomp stream pointer to caller
> > - if idle list is empty, current adds itself to wait queue. it will be
> >   awaken by zcomp_strm_put() caller.
> > 
> > zcomp_strm_put():
> > - spin lock strm_lock
> > - add zcomp stream to idle list
> > - spin unlock, wake up sleeper
> > 
> > In other words, zcomp_strm_get() turns caller into exclusive user of a stream
> > and zcomp_strm_put() makes a particular zcomp stream available.
> > 
> > Usage examples.
> > 
> > To initialize compressing backend:
> > 	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>
> 
> Just minor nitpicks below.

thanks, will address.

> > ---
> >  drivers/block/zram/zcomp.c     | 151 +++++++++++++++++++++++++++++++++++++++++
> >  drivers/block/zram/zcomp.h     |  56 +++++++++++++++
> >  drivers/block/zram/zcomp_lzo.c |  48 +++++++++++++
> >  3 files changed, 255 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..3af25b6
> > --- /dev/null
> > +++ b/drivers/block/zram/zcomp.c
> > @@ -0,0 +1,151 @@
> > +/*
> > + * 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 void zcomp_strm_free(struct zcomp *comp, struct zcomp_strm *zstrm)
> > +{
> > +	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;
> > +
> > +	INIT_LIST_HEAD(&zstrm->list);
> 
> No need to initialize.
> 
> > +	zstrm->private = comp->backend->create();
> 
> Pz, check zstrm->private NULL and handle it out.
> Otherwise, zcomp_strm_free could pass NULL with backend's destroy
> so all of backend should handle NULL argument, which is not good for me.
> 

yes, at the moment it will not cause any problems (passing NULL to kfree()),
but in general case it makes sense.

> > +	/*
> > +	 * 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;
> > +}
> > +
> > +/*
> > + * get existing idle zcomp_strm or wait until other process release
> > + * (zcomp_strm_put()) one for us
> > + */
> > +struct zcomp_strm *zcomp_strm_get(struct zcomp *comp)
> > +{
> > +	struct zcomp_strm *zstrm;
> > +
> > +	while (1) {
> > +		spin_lock(&comp->strm_lock);
> > +		if (list_empty(&comp->idle_strm)) {
> > +			spin_unlock(&comp->strm_lock);
> > +			wait_event(comp->strm_wait,
> > +					!list_empty(&comp->idle_strm));
> > +			continue;
> > +		}
> > +
> > +		zstrm = list_entry(comp->idle_strm.next,
> > +				struct zcomp_strm, list);
> > +		list_del(&zstrm->list);
> > +		spin_unlock(&comp->strm_lock);
> > +		break;
> > +	}
> > +	return zstrm;
> > +}
> > +
> > +/* add zcomp_strm back to idle list and wake up waiter (if any) */
> > +void zcomp_strm_put(struct zcomp *comp, struct zcomp_strm *zstrm)
> > +{
> > +	spin_lock(&comp->strm_lock);
> > +	list_add(&zstrm->list, &comp->idle_strm);
> > +	spin_unlock(&comp->strm_lock);
> > +
> > +	wake_up(&comp->strm_wait);
> > +}
> > +
> > +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)
> > +{
> > +	struct zcomp_strm *zstrm;
> > +	while (!list_empty(&comp->idle_strm)) {
> > +		zstrm = list_entry(comp->idle_strm.next,
> > +				struct zcomp_strm, list);
> > +		list_del(&zstrm->list);
> > +		zcomp_strm_free(comp, zstrm);
> > +	}
> > +	kfree(comp);
> > +}
> 
> You made zcom_destroy but I couldn't find zcomp_create?
> 

it's several lines below :)

> > +
> > +static struct zcomp_backend *find_backend(const char *compress)
> > +{
> > +	if (sysfs_streq(compress, "lzo"))
> 
> Why do you use sysfs_streq?
> It's not sysfs variable yet.

yep.

> > +		return &zcomp_lzo;
> > +	return NULL;
> > +}
> > +
> > +/*
> > + * 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)

		^^^^^^^^^^^^^^^^^

here it is.

> > +{
> > +	struct zcomp *comp;
> > +	struct zcomp_backend *backend;
> > +	struct zcomp_strm *zstrm;
> > +
> > +	backend = find_backend(compress);
> > +	if (!backend)
> > +		return NULL;
> > +
> > +	comp = kmalloc(sizeof(struct zcomp), GFP_KERNEL);
> > +	if (!comp)
> > +		return NULL;
> > +
> > +	comp->backend = backend;
> > +	spin_lock_init(&comp->strm_lock);
> > +	INIT_LIST_HEAD(&comp->idle_strm);
> > +	init_waitqueue_head(&comp->strm_wait);
> > +
> > +	zstrm = zcomp_strm_alloc(comp);
> > +	if (!zstrm) {
> > +		zcomp_destroy(comp);
> > +		return NULL;
> > +	}
> > +	list_add(&zstrm->list, &comp->idle_strm);
> > +	return comp;
> > +}
> > diff --git a/drivers/block/zram/zcomp.h b/drivers/block/zram/zcomp.h
> > new file mode 100644
> > index 0000000..7e05d20
> > --- /dev/null
> > +++ b/drivers/block/zram/zcomp.h
> > @@ -0,0 +1,56 @@
> > +/*
> > + * 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.
> > + */
> > +
> > +#ifndef _ZCOMP_H_
> > +#define _ZCOMP_H_
> > +
> > +#include <linux/spinlock.h>
> > +
> > +struct zcomp_strm {
> > +	void *buffer;     /* compression/decompression buffer */
> > +	void *private;      /* algorithm private memory */
> 
>          							It's not a *memory*.
> 									

	ok

> > +	struct list_head list;
> > +};
> > +
> > +/* static compression backend */
> > +struct zcomp_backend {
> > +	int (*compress)(const unsigned char *src, unsigned char *dst,
> > +			size_t *dst_len, void *private);
> > +
> > +	int (*decompress)(const unsigned char *src, size_t src_len,
> > +			unsigned char *dst);
> > +
> > +	void * (*create)(void);
> > +	void (*destroy)(void *private);
> > +
> > +	const char *name;
> > +};
> > +
> > +/* dynamic per-device compression frontend */
> > +struct zcomp {
> > +	/* protect strm list */
> > +	spinlock_t strm_lock;
> > +	/* list of available strms */
> > +	struct list_head idle_strm;
> > +	wait_queue_head_t strm_wait;
> > +	struct zcomp_backend *backend;
> > +};
> > +
> > +struct zcomp *zcomp_create(const char *comp);
> > +void zcomp_destroy(struct zcomp *comp);
> > +
> > +struct zcomp_strm *zcomp_strm_get(struct zcomp *comp);
> > +void zcomp_strm_put(struct zcomp *comp, struct zcomp_strm *zstrm);
> > +
> > +int zcomp_compress(struct zcomp *comp, struct zcomp_strm *zstrm,
> > +		const unsigned char *src, size_t *dst_len);
> > +
> > +int zcomp_decompress(struct zcomp *comp, const unsigned char *src,
> > +		size_t src_len, unsigned char *dst);
> > +#endif /* _ZCOMP_H_ */
> > diff --git a/drivers/block/zram/zcomp_lzo.c b/drivers/block/zram/zcomp_lzo.c
> > new file mode 100644
> > index 0000000..39106a7
> > --- /dev/null
> > +++ b/drivers/block/zram/zcomp_lzo.c
> > @@ -0,0 +1,48 @@
> > +/*
> > + * 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/slab.h>
> > +#include <linux/lzo.h>
> > +
> > +#include "zcomp.h"
> > +
> > +static void * lzo_create(void)
>                 ^
>           unnecessary white space
> 
> > +{
> > +	return kzalloc(LZO1X_MEM_COMPRESS, GFP_KERNEL);
> > +}
> > +
> > +static void lzo_destroy(void *private)
> > +{
> > +	kfree(private);
> > +}
> > +
> > +static int lzo_compress(const unsigned char *src, unsigned char *dst,
> > +		size_t *dst_len, void *private)
> > +{
> > +	int ret = lzo1x_1_compress(src, PAGE_SIZE, dst, dst_len, private);
> > +	return ret == LZO_E_OK ? 0 : ret;
> > +}
> > +
> > +static int lzo_decompress(const unsigned char *src, size_t src_len,
> > +		unsigned char *dst)
> > +{
> > +	size_t dst_len = PAGE_SIZE;
> > +	int ret = lzo1x_decompress_safe(src, src_len, dst, &dst_len);
> > +	return ret == LZO_E_OK ? 0 : ret;
> > +}
> > +
> > +extern struct zcomp_backend zcomp_lzo;
> > +struct zcomp_backend zcomp_lzo = {
> > +	.compress = lzo_compress,
> > +	.decompress = lzo_decompress,
> > +	.create = lzo_create,
> > +	.destroy = lzo_destroy,
> > +	.name = "lzo",
> > +};
> > -- 
> > 1.9.0.rc3.260.g4cf525c
> > 
> 
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