[PATCHv7 4/7] zram: add multi stream functionality

Sergey Senozhatsky
2014-02-25T11:39:49Z

This patch implements multi stream compression support.

Introduce struct zcomp_strm_multi and a set of functions to manage
zcomp_strm stream access. zcomp_strm_multi has a list of idle zcomp_strm
structs, spinlock to protect idle list and wait queue, making it possible
to perform parallel compressions.

The following set of functions added:
- zcomp_strm_multi_get()/zcomp_strm_multi_put()
get and put compression stream, implement required locking
- zcomp_strm_multi_create()/zcomp_strm_multi_destroy()
create and destroy zcomp_strm_multi

zcomp ->strm_get() and ->strm_put() callbacks are set during initialisation
to zcomp_strm_multi_get()/zcomp_strm_multi_put() correspondingly.

Each time zcomp issues a zcomp_strm_multi_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_multi_put() caller.

zcomp_strm_multi_put():
- spin lock strm_lock
- add zcomp stream to idle list
- spin unlock, wake up sleeper

Minchan Kim reported that spinlock-based locking scheme has demonstrated a
severe perfomance regression for single compression stream case, comparing
to mutex-based (https://lkml.org/lkml/2014/2/18/16)

base spinlock mutex

==Initial write ==Initial write ==Initial write
records: 5 records: 5 records: 5
avg: 1642424.35 avg: 699610.40 avg: 1655583.71
std: 39890.95(2.43%) std: 232014.19(33.16%) std: 52293.96
max: 1690170.94 max: 1163473.45 max: 1697164.75
min: 1568669.52 min: 573429.88 min: 1553410.23
==Rewrite ==Rewrite ==Rewrite
records: 5 records: 5 records: 5
avg: 1611775.39 avg: 501406.64 avg: 1684419.11
std: 17144.58(1.06%) std: 15354.41(3.06%) std: 18367.42
max: 1641800.95 max: 531356.78 max: 1706445.84
min: 1593515.27 min: 488817.78 min: 1655335.73
==Random write ==Random write ==Random write
records: 5 records: 5 records: 5
avg: 1626318.29 avg: 497250.78 avg: 1695582.06
std: 38550.23(2.37%) std: 1405.42(0.28%) std: 9211.98
max: 1665839.62 max: 498585.88 max: 1703808.22
min: 1562141.21 min: 494526.45 min: 1677664.94
==Pwrite ==Pwrite ==Pwrite
records: 5 records: 5 records: 5
avg: 1654641.25 avg: 581709.22 avg: 1641452.34
std: 47202.59(2.85%) std: 9670.46(1.66%) std: 38963.62
max: 1740682.36 max: 591300.09 max: 1687387.69
min: 1611436.34 min: 564324.38 min: 1570496.11

When only one compression stream available, mutex with spin on owner tends
to perform much better than frequent wait_event()/wake_up(). This is why
single stream implemented as a special case with mutex locking.

This is preparation patch, later patches will use this code.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
drivers/block/zram/zcomp.c | 119 ++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 118 insertions(+), 1 deletion(-)

diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
index e20054b..6f238f5 100644
--- a/drivers/block/zram/zcomp.c
+++ b/drivers/block/zram/zcomp.c
@@ -15,6 +15,8 @@

#include "zcomp.h"

+extern struct zcomp_backend zcomp_lzo;
+
/*
* single zcomp_strm backend
*/
@@ -23,7 +25,20 @@ struct zcomp_strm_single {
struct zcomp_strm *zstrm;
};

-extern struct zcomp_backend zcomp_lzo;
+/*
+ * multi zcomp_strm backend
+ */
+struct zcomp_strm_multi {
+ /* protect strm list */
+ spinlock_t strm_lock;
+ /* max possible number of zstrm streams */
+ int max_strm;
+ /* number of available zstrm streams */
+ atomic_t avail_strm;
+ /* list of available strms */
+ struct list_head idle_strm;
+ wait_queue_head_t strm_wait;
+};

static struct zcomp_backend *find_backend(const char *compress)
{
@@ -63,6 +78,108 @@ static struct zcomp_strm *zcomp_strm_alloc(struct zcomp *comp)
return zstrm;
}

+/*
+ * get idle zcomp_strm or wait until other process release
+ * (zcomp_strm_put()) one for us
+ */
+static struct zcomp_strm *zcomp_strm_multi_get(struct zcomp *comp)
+{
+ struct zcomp_strm_multi *zs = comp->stream;
+ struct zcomp_strm *zstrm;
+
+ while (1) {
+ spin_lock(&zs->strm_lock);
+ if (!list_empty(&zs->idle_strm)) {
+ zstrm = list_entry(zs->idle_strm.next,
+ struct zcomp_strm, list);
+ list_del(&zstrm->list);
+ spin_unlock(&zs->strm_lock);
+ return zstrm;
+ }
+ /* zstrm streams limit reached, wait for idle stream */
+ if (atomic_read(&zs->avail_strm) >= zs->max_strm) {
+ spin_unlock(&zs->strm_lock);
+ wait_event(zs->strm_wait, !list_empty(&zs->idle_strm));
+ continue;
+ }
+ /* allocate new zstrm stream */
+ atomic_inc(&zs->avail_strm);
+ spin_unlock(&zs->strm_lock);
+
+ zstrm = zcomp_strm_alloc(comp);
+ if (!zstrm) {
+ atomic_dec(&zs->avail_strm);
+ wait_event(zs->strm_wait, !list_empty(&zs->idle_strm));
+ continue;
+ }
+ break;
+ }
+ return zstrm;
+}
+
+/* add stream back to idle list and wake up waiter or free the stream */
+static void zcomp_strm_multi_put(struct zcomp *comp, struct zcomp_strm *zstrm)
+{
+ struct zcomp_strm_multi *zs = comp->stream;
+
+ spin_lock(&zs->strm_lock);
+ if (atomic_read(&zs->avail_strm) <= zs->max_strm) {
+ list_add(&zstrm->list, &zs->idle_strm);
+ spin_unlock(&zs->strm_lock);
+ } else {
+ atomic_dec(&zs->avail_strm);
+ spin_unlock(&zs->strm_lock);
+ zcomp_strm_free(comp, zstrm);
+ }
+
+ wake_up(&zs->strm_wait);
+}
+
+static void zcomp_strm_multi_destroy(struct zcomp *comp)
+{
+ struct zcomp_strm_multi *zs = comp->stream;
+ struct zcomp_strm *zstrm;
+
+ while (!list_empty(&zs->idle_strm)) {
+ zstrm = list_entry(zs->idle_strm.next,
+ struct zcomp_strm, list);
+ list_del(&zstrm->list);
+ zcomp_strm_free(comp, zstrm);
+ }
+ kfree(zs);
+}
+
+static int zcomp_strm_multi_create(struct zcomp *comp, int num_strm)
+{
+ struct zcomp_strm *zstrm;
+ struct zcomp_strm_multi *zs;
+ int i;
+
+ comp->destroy = zcomp_strm_multi_destroy;
+ comp->strm_get = zcomp_strm_multi_get;
+ comp->strm_put = zcomp_strm_multi_put;
+ zs = kmalloc(sizeof(struct zcomp_strm_multi), GFP_KERNEL);
+ comp->stream = zs;
+ if (!zs)
+ return -ENOMEM;
+
+ spin_lock_init(&zs->strm_lock);
+ INIT_LIST_HEAD(&zs->idle_strm);
+ init_waitqueue_head(&zs->strm_wait);
+ zs->max_strm = num_strm;
+ atomic_set(&zs->avail_strm, num_strm);
+
+ for (i = 0; i < num_strm; i++) {
+ zstrm = zcomp_strm_alloc(comp);
+ if (!zstrm) {
+ zcomp_strm_multi_destroy(comp);
+ return -ENOMEM;
+ }
+ list_add(&zstrm->list, &zs->idle_strm);
+ }
+ return 0;
+}
+
static struct zcomp_strm *zcomp_strm_single_get(struct zcomp *comp)
{
struct zcomp_strm_single *zs = comp->stream;
--
1.9.0.291.g027825b