[PATCH 1/3] zram: allow user to set QUEUE_FLAG_NOWAIT

[Chaitanya Kulkarni <kch@nvidia.com>]

Allow user to set the QUEUE_FLAG_NOWAIT optionally using module
parameter to retain the default behaviour. Also, update respective
allocation flags in the write path. Following are the performance
numbers with io_uring fio engine for random read, note that device has
been populated fully with randwrite workload before taking these
numbers :-

* linux-block (for-next) # grep IOPS  zram*fio | column -t 

default-nowait-off-1.fio:  read:  IOPS=802k,  BW=3133MiB/s
default-nowait-off-2.fio:  read:  IOPS=796k,  BW=3111MiB/s
default-nowait-off-3.fio:  read:  IOPS=796k,  BW=3108MiB/s

nowait-on-1.fio:           read:  IOPS=857k,  BW=3346MiB/s
nowait-on-2.fio:           read:  IOPS=857k,  BW=3347MiB/s
nowait-on-3.fio:           read:  IOPS=858k,  BW=3353MiB/s

* linux-block (for-next) # grep cpu  zram*fio | column -t 
default-nowait-off-1.fio:  cpu  :  usr=5.82%,  sys=13.54%,  ctx=36301915
default-nowait-off-2.fio:  cpu  :  usr=5.84%,  sys=13.03%,  ctx=37781937
default-nowait-off-3.fio:  cpu  :  usr=5.84%,  sys=12.90%,  ctx=37492533

nowait-on-1.fio:           cpu  :  usr=1.74%,  sys=97.62%,  ctx=24068,  
nowait-on-2.fio:           cpu  :  usr=1.74%,  sys=97.57%,  ctx=24674,  
nowait-on-3.fio:           cpu  :  usr=1.76%,  sys=97.59%,  ctx=24725,  

Signed-off-by: Chaitanya Kulkarni <kch@nvidia.com>
---
 drivers/block/zram/zram_drv.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index f6d90f1ba5cf..b2e419f15f71 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -36,6 +36,10 @@
 
 #include "zram_drv.h"
 
+static bool g_nowait;
+module_param_named(nowait, g_nowait, bool, 0444);
+MODULE_PARM_DESC(nowait, "set QUEUE_FLAG_NOWAIT. Default: False");
+
 static DEFINE_IDR(zram_index_idr);
 /* idr index must be protected */
 static DEFINE_MUTEX(zram_index_mutex);
@@ -1540,9 +1544,10 @@ static int zram_write_page(struct zram *zram, struct page *page, u32 index)
 static int zram_bvec_write_partial(struct zram *zram, struct bio_vec *bvec,
 				   u32 index, int offset, struct bio *bio)
 {
-	struct page *page = alloc_page(GFP_NOIO);
+	struct page *page;
 	int ret;
 
+	page = alloc_page(bio->bi_opf & REQ_NOWAIT ? GFP_NOWAIT : GFP_NOIO);
 	if (!page)
 		return -ENOMEM;
 
@@ -2215,6 +2220,8 @@ static int zram_add(void)
 	/* zram devices sort of resembles non-rotational disks */
 	blk_queue_flag_set(QUEUE_FLAG_NONROT, zram->disk->queue);
 	blk_queue_flag_set(QUEUE_FLAG_SYNCHRONOUS, zram->disk->queue);
+	if (g_nowait)
+		blk_queue_flag_set(QUEUE_FLAG_NOWAIT, zram->disk->queue);
 
 	/*
 	 * To ensure that we always get PAGE_SIZE aligned
-- 
2.40.0