Messages in this thread | | | Date | Tue, 18 Feb 2014 05:10:25 +0000 | From | Minchan Kim <> | Subject | Re: [PATCHv5 1/4] zram: introduce compressing backend abstraction |
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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@gmail.com>
Just minor nitpicks below.
> --- > 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.
> + /* > + * 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?
> + > +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.
> + 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) > +{ > + 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*.
> + 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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