zram: introduce zram->tb_lock

Currently, the zram 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.

Change-Id: If5456f871bc6b0d6ee1f8218fde3f5a13d261c8b
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Tested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index b22caa8..630a97b 100644 (file)
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/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/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 81b0170..c3f453f 100644 (file)
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -83,6 +83,7 @@ struct zram_stats {
 };
 
 struct zram_meta {
+       rwlock_t tb_lock;       /* protect table */
        void *compress_workmem;
        void *compress_buffer;
        struct table *table;
@@ -96,7 +97,7 @@ 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
                                   */