zram: remove zram->lock in read path and change it with mutex

Finally, we separated zram->lock dependency from 32bit stat/ table
handling so there is no reason to use rw_semaphore between read and
write path so this patch removes the lock from read path totally and
changes rw_semaphore with mutex.  So, we could do

old:

  read-read: OK
  read-write: NO
  write-write: NO

Now:

  read-read: OK
  read-write: OK
  write-write: NO

The below data proves mixed workload performs well 11 times and there is
also enhance on write-write path because current rw-semaphore doesn't
support SPIN_ON_OWNER.  It's side effect but anyway good thing for us.

Write-related tests perform better (from 61% to 1058%) but read path has
good/bad(from -2.22% to 1.45%) but they are all marginal within stddev.

  CPU 12
  iozone -t -T -l 12 -u 12 -r 16K -s 60M -I +Z -V 0

  ==Initial write                ==Initial write
  records: 10                    records: 10
  avg:  516189.16                avg:  839907.96
  std:   22486.53 (4.36%)        std:   47902.17 (5.70%)
  max:  546970.60                max:  909910.35
  min:  481131.54                min:  751148.38
  ==Rewrite                      ==Rewrite
  records: 10                    records: 10
  avg:  509527.98                avg: 1050156.37
  std:   45799.94 (8.99%)        std:   40695.44 (3.88%)
  max:  611574.27                max: 1111929.26
  min:  443679.95                min:  980409.62
  ==Read                         ==Read
  records: 10                    records: 10
  avg: 4408624.17                avg: 4472546.76
  std:  281152.61 (6.38%)        std:  163662.78 (3.66%)
  max: 4867888.66                max: 4727351.03
  min: 4058347.69                min: 4126520.88
  ==Re-read                      ==Re-read
  records: 10                    records: 10
  avg: 4462147.53                avg: 4363257.75
  std:  283546.11 (6.35%)        std:  247292.63 (5.67%)
  max: 4912894.44                max: 4677241.75
  min: 4131386.50                min: 4035235.84
  ==Reverse Read                 ==Reverse Read
  records: 10                    records: 10
  avg: 4565865.97                avg: 4485818.08
  std:  313395.63 (6.86%)        std:  248470.10 (5.54%)
  max: 5232749.16                max: 4789749.94
  min: 4185809.62                min: 3963081.34
  ==Stride read                  ==Stride read
  records: 10                    records: 10
  avg: 4515981.80                avg: 4418806.01
  std:  211192.32 (4.68%)        std:  212837.97 (4.82%)
  max: 4889287.28                max: 4686967.22
  min: 4210362.00                min: 4083041.84
  ==Random read                  ==Random read
  records: 10                    records: 10
  avg: 4410525.23                avg: 4387093.18
  std:  236693.22 (5.37%)        std:  235285.23 (5.36%)
  max: 4713698.47                max: 4669760.62
  min: 4057163.62                min: 3952002.16
  ==Mixed workload               ==Mixed workload
  records: 10                    records: 10
  avg:  243234.25                avg: 2818677.27
  std:   28505.07 (11.72%)       std:  195569.70 (6.94%)
  max:  288905.23                max: 3126478.11
  min:  212473.16                min: 2484150.69
  ==Random write                 ==Random write
  records: 10                    records: 10
  avg:  555887.07                avg: 1053057.79
  std:   70841.98 (12.74%)       std:   35195.36 (3.34%)
  max:  683188.28                max: 1096125.73
  min:  437299.57                min:  992481.93
  ==Pwrite                       ==Pwrite
  records: 10                    records: 10
  avg:  501745.93                avg:  810363.09
  std:   16373.54 (3.26%)        std:   19245.01 (2.37%)
  max:  518724.52                max:  833359.70
  min:  464208.73                min:  765501.87
  ==Pread                        ==Pread
  records: 10                    records: 10
  avg: 4539894.60                avg: 4457680.58
  std:  197094.66 (4.34%)        std:  188965.60 (4.24%)
  max: 4877170.38                max: 4689905.53
  min: 4226326.03                min: 4095739.72

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>

drivers/block/zram/zram_drv.c

@@ -230,6 +230,7 @@ static struct zram_meta *zram_meta_alloc(u64 disksize)
 	}
 
 	rwlock_init(&meta->tb_lock);
+	mutex_init(&meta->buffer_lock);
 	return meta;
 
 free_table:
@@ -412,6 +413,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 	struct page *page;
 	unsigned char *user_mem, *cmem, *src, *uncmem = NULL;
 	struct zram_meta *meta = zram->meta;
+	bool locked = false;
 
 	page = bvec->bv_page;
 	src = meta->compress_buffer;
@@ -431,6 +433,8 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 			goto out;
 	}
 
+	mutex_lock(&meta->buffer_lock);
+	locked = true;
 	user_mem = kmap_atomic(page);
 
 	if (is_partial_io(bvec)) {
@@ -457,7 +461,6 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 
 	ret = lzo1x_1_compress(uncmem, PAGE_SIZE, src, &clen,
 			       meta->compress_workmem);
-
 	if (!is_partial_io(bvec)) {
 		kunmap_atomic(user_mem);
 		user_mem = NULL;
@@ -514,6 +517,8 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 		atomic_inc(&zram->stats.good_compress);
 
 out:
+	if (locked)
+		mutex_unlock(&meta->buffer_lock);
 	if (is_partial_io(bvec))
 		kfree(uncmem);
 
@@ -527,15 +532,10 @@ static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
 {
 	int ret;
 
-	if (rw == READ) {
-		down_read(&zram->lock);
+	if (rw == READ)
 		ret = zram_bvec_read(zram, bvec, index, offset, bio);
-		up_read(&zram->lock);
-	} else {
-		down_write(&zram->lock);
+	else
 		ret = zram_bvec_write(zram, bvec, index, offset);
-		up_write(&zram->lock);
-	}
 
 	return ret;
 }
@@ -808,7 +808,6 @@ static int create_device(struct zram *zram, int device_id)
 {
 	int ret = -ENOMEM;
 
-	init_rwsem(&zram->lock);
 	init_rwsem(&zram->init_lock);
 
 	zram->queue = blk_alloc_queue(GFP_KERNEL);

drivers/block/zram/zram_drv.h

@@ -88,13 +88,11 @@ struct zram_meta {
 	void *compress_buffer;
 	struct table *table;
 	struct zs_pool *mem_pool;
+	struct mutex buffer_lock; /* protect compress buffers */
 };
 
 struct zram {
 	struct zram_meta *meta;
-	struct rw_semaphore lock; /* protect compression buffers,
-				   * reads and writes
-				   */
 	struct request_queue *queue;
 	struct gendisk *disk;
 	int init_done;