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Subject[PATCHv9 3/7] zram: factor out single stream compression
Date
This is preparation patch to add multi stream support to zcomp.

Introduce struct zcomp_strm_single and a set of functions to manage zcomp_strm
stream access. zcomp_strm_single implements single compession stream, same way
as current zcomp implementation. This moves zcomp_strm stream control and
locking from zcomp, so compressing backend zcomp is not aware of required
locking.

Single and multi streams require different locking schemes. Minchan Kim
reported that spinlock-based locking scheme (which is used in multi stream
implementation) has demonstrated a severe perfomance regression for single
compression stream case, comparing to mutex-based.
see https://lkml.org/lkml/2014/2/18/16

The following set of functions added:
- zcomp_strm_single_find()/zcomp_strm_single_release()
find and release a compression stream, implement required locking
- zcomp_strm_single_create()/zcomp_strm_single_destroy()
create and destroy zcomp_strm_single

New ->strm_find() and ->strm_release() callbacks added to zcomp, which are set to
zcomp_strm_single_find() and zcomp_strm_single_release() during initialisation.
Instead of direct locking and zcomp_strm access from zcomp_strm_find() and
zcomp_strm_release(), zcomp now calls ->strm_find() and ->strm_release()
correspondingly.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
drivers/block/zram/zcomp.c | 62 ++++++++++++++++++++++++++++++++++++++++------
drivers/block/zram/zcomp.h | 7 ++++--
2 files changed, 59 insertions(+), 10 deletions(-)

diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
index 22f4ae2..72e8071 100644
--- a/drivers/block/zram/zcomp.c
+++ b/drivers/block/zram/zcomp.c
@@ -16,6 +16,14 @@
#include "zcomp.h"
#include "zcomp_lzo.h"

+/*
+ * single zcomp_strm backend
+ */
+struct zcomp_strm_single {
+ struct mutex strm_lock;
+ struct zcomp_strm *zstrm;
+};
+
static struct zcomp_backend *find_backend(const char *compress)
{
if (strncmp(compress, "lzo", 3) == 0)
@@ -54,15 +62,56 @@ static struct zcomp_strm *zcomp_strm_alloc(struct zcomp *comp)
return zstrm;
}

+static struct zcomp_strm *zcomp_strm_single_find(struct zcomp *comp)
+{
+ struct zcomp_strm_single *zs = comp->stream;
+ mutex_lock(&zs->strm_lock);
+ return zs->zstrm;
+}
+
+static void zcomp_strm_single_release(struct zcomp *comp,
+ struct zcomp_strm *zstrm)
+{
+ struct zcomp_strm_single *zs = comp->stream;
+ mutex_unlock(&zs->strm_lock);
+}
+
+static void zcomp_strm_single_destroy(struct zcomp *comp)
+{
+ struct zcomp_strm_single *zs = comp->stream;
+ zcomp_strm_free(comp, zs->zstrm);
+ kfree(zs);
+}
+
+static int zcomp_strm_single_create(struct zcomp *comp)
+{
+ struct zcomp_strm_single *zs;
+
+ comp->destroy = zcomp_strm_single_destroy;
+ comp->strm_find = zcomp_strm_single_find;
+ comp->strm_release = zcomp_strm_single_release;
+ zs = kmalloc(sizeof(struct zcomp_strm_single), GFP_KERNEL);
+ if (!zs)
+ return -ENOMEM;
+
+ comp->stream = zs;
+ mutex_init(&zs->strm_lock);
+ zs->zstrm = zcomp_strm_alloc(comp);
+ if (!zs->zstrm) {
+ kfree(zs);
+ return -ENOMEM;
+ }
+ return 0;
+}
+
struct zcomp_strm *zcomp_strm_find(struct zcomp *comp)
{
- mutex_lock(&comp->strm_lock);
- return comp->zstrm;
+ return comp->strm_find(comp);
}

void zcomp_strm_release(struct zcomp *comp, struct zcomp_strm *zstrm)
{
- mutex_unlock(&comp->strm_lock);
+ comp->strm_release(comp, zstrm);
}

int zcomp_compress(struct zcomp *comp, struct zcomp_strm *zstrm,
@@ -80,7 +129,7 @@ int zcomp_decompress(struct zcomp *comp, const unsigned char *src,

void zcomp_destroy(struct zcomp *comp)
{
- zcomp_strm_free(comp, comp->zstrm);
+ comp->destroy(comp);
kfree(comp);
}

@@ -104,10 +153,7 @@ struct zcomp *zcomp_create(const char *compress)
return NULL;

comp->backend = backend;
- mutex_init(&comp->strm_lock);
-
- comp->zstrm = zcomp_strm_alloc(comp);
- if (!comp->zstrm) {
+ if (zcomp_strm_single_create(comp) != 0) {
kfree(comp);
return NULL;
}
diff --git a/drivers/block/zram/zcomp.h b/drivers/block/zram/zcomp.h
index c9a98e1..dc3500d 100644
--- a/drivers/block/zram/zcomp.h
+++ b/drivers/block/zram/zcomp.h
@@ -39,9 +39,12 @@ struct zcomp_backend {

/* dynamic per-device compression frontend */
struct zcomp {
- struct mutex strm_lock;
- struct zcomp_strm *zstrm;
+ void *stream;
struct zcomp_backend *backend;
+
+ struct zcomp_strm *(*strm_find)(struct zcomp *comp);
+ void (*strm_release)(struct zcomp *comp, struct zcomp_strm *zstrm);
+ void (*destroy)(struct zcomp *comp);
};

struct zcomp *zcomp_create(const char *comp);
--
1.9.0.359.g5e34a15


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