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Date: Wed, 15 Jan 2014 10:11:08 +0900
From: Minchan Kim <minchan@...nel.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, Nitin Gupta <ngupta@...are.org>,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
Jerome Marchand <jmarchan@...hat.com>,
Minchan Kim <minchan@...nel.org>
Subject: [PATCH v2 2/4] zram: introduce zram->tb_lock
Currently, table is protected by zram->lock but it's rather
coarse-grained lock and it makes hard for scalibility.
Let's use own rwlock instead of depending on zram->lock.
This patch adds new locking so obviously, it would make slow
but this patch is just prepartion for removing coarse-grained
rw_semaphore(ie, zram->lock) which is hurdle about zram
scalability.
Final patch in this patchset series will remove the lock
from read-path and change rw_semaphore with mutex in write path.
With bonus, we could drop pending slot free mess in next patch.
Signed-off-by: Minchan Kim <minchan@...nel.org>
---
drivers/staging/zram/zram_drv.c | 26 +++++++++++++++++++++-----
drivers/staging/zram/zram_drv.h | 3 ++-
2 files changed, 23 insertions(+), 6 deletions(-)
diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index 6613225dfca1..8636f8511518 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -140,6 +140,7 @@ static ssize_t mem_used_total_show(struct device *dev,
return sprintf(buf, "%llu\n", val);
}
+/* flag operations needs meta->tb_lock */
static int zram_test_flag(struct zram_meta *meta, u32 index,
enum zram_pageflags flag)
{
@@ -227,6 +228,7 @@ static struct zram_meta *zram_meta_alloc(u64 disksize)
goto free_table;
}
+ rwlock_init(&meta->tb_lock);
return meta;
free_table:
@@ -279,6 +281,7 @@ static void handle_zero_page(struct bio_vec *bvec)
flush_dcache_page(page);
}
+/* NOTE: caller should hold meta->tb_lock with write-side */
static void zram_free_page(struct zram *zram, size_t index)
{
struct zram_meta *meta = zram->meta;
@@ -318,20 +321,26 @@ static int zram_decompress_page(struct zram *zram, char *mem, u32 index)
size_t clen = PAGE_SIZE;
unsigned char *cmem;
struct zram_meta *meta = zram->meta;
- unsigned long handle = meta->table[index].handle;
+ unsigned long handle;
+ u16 size;
+
+ read_lock(&meta->tb_lock);
+ handle = meta->table[index].handle;
+ size = meta->table[index].size;
if (!handle || zram_test_flag(meta, index, ZRAM_ZERO)) {
+ read_unlock(&meta->tb_lock);
clear_page(mem);
return 0;
}
cmem = zs_map_object(meta->mem_pool, handle, ZS_MM_RO);
- if (meta->table[index].size == PAGE_SIZE)
+ if (size == PAGE_SIZE)
copy_page(mem, cmem);
else
- ret = lzo1x_decompress_safe(cmem, meta->table[index].size,
- mem, &clen);
+ ret = lzo1x_decompress_safe(cmem, size, mem, &clen);
zs_unmap_object(meta->mem_pool, handle);
+ read_unlock(&meta->tb_lock);
/* Should NEVER happen. Return bio error if it does. */
if (unlikely(ret != LZO_E_OK)) {
@@ -352,11 +361,14 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
struct zram_meta *meta = zram->meta;
page = bvec->bv_page;
+ read_lock(&meta->tb_lock);
if (unlikely(!meta->table[index].handle) ||
zram_test_flag(meta, index, ZRAM_ZERO)) {
+ read_unlock(&meta->tb_lock);
handle_zero_page(bvec);
return 0;
}
+ read_unlock(&meta->tb_lock);
if (is_partial_io(bvec))
/* Use a temporary buffer to decompress the page */
@@ -432,10 +444,12 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
if (page_zero_filled(uncmem)) {
kunmap_atomic(user_mem);
/* Free memory associated with this sector now. */
+ write_lock(&zram->meta->tb_lock);
zram_free_page(zram, index);
+ zram_set_flag(meta, index, ZRAM_ZERO);
+ write_unlock(&zram->meta->tb_lock);
atomic_inc(&zram->stats.pages_zero);
- zram_set_flag(meta, index, ZRAM_ZERO);
ret = 0;
goto out;
}
@@ -485,10 +499,12 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
* Free memory associated with this sector
* before overwriting unused sectors.
*/
+ write_lock(&zram->meta->tb_lock);
zram_free_page(zram, index);
meta->table[index].handle = handle;
meta->table[index].size = clen;
+ write_unlock(&zram->meta->tb_lock);
/* Update stats */
atomic64_add(clen, &zram->stats.compr_size);
diff --git a/drivers/staging/zram/zram_drv.h b/drivers/staging/zram/zram_drv.h
index 459483966c3d..cf64bea3f7cc 100644
--- a/drivers/staging/zram/zram_drv.h
+++ b/drivers/staging/zram/zram_drv.h
@@ -84,6 +84,7 @@ struct zram_stats {
};
struct zram_meta {
+ rwlock_t tb_lock; /* protect table */
void *compress_workmem;
void *compress_buffer;
struct table *table;
@@ -97,7 +98,7 @@ struct zram_slot_free {
struct zram {
struct zram_meta *meta;
- struct rw_semaphore lock; /* protect compression buffers, table,
+ struct rw_semaphore lock; /* protect compression buffers,
* reads and writes
*/
--
1.8.5.2
--
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