[PATCH v2] zram: don't retry compress incompressible page

[PATCH v2] zram: don't retry compress incompressible page

[Alexey Romanov]

It doesn't make sense for us to retry to compress an uncompressible
page (comp_len == PAGE_SIZE) in zsmalloc slowpath, because we will
be storing it uncompressed anyway. We can avoid wasting time on
another compression attempt. It is enough to take lock
(zcomp_stream_get) and execute the code below.

Signed-off-by: Alexey Romanov <avromanov@sberdevices.ru>
Signed-off-by: Dmitry Rokosov <ddrokosov@sberdevices.ru>
---
 drivers/block/zram/zram_drv.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 226ea76cc819..3bd8d5e27041 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1410,9 +1410,19 @@ static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 		handle = zs_malloc(zram->mem_pool, comp_len,
 				GFP_NOIO | __GFP_HIGHMEM |
 				__GFP_MOVABLE);
-		if (!IS_ERR((void *)handle))
+		if (IS_ERR((void *)handle))
+			return PTR_ERR((void *)handle);
+
+		if (comp_len != PAGE_SIZE)
 			goto compress_again;
-		return PTR_ERR((void *)handle);
+		/*
+		 * If the page is not compressible, you need to acquire the lock and
+		 * execute the code below. The zcomp_stream_get() call is needed to
+		 * disable the cpu hotplug and grab the zstrm buffer back.
+		 * It is necessary that the dereferencing of the zstrm variable below
+		 * occurs correctly.
+		 */
+		zstrm = zcomp_stream_get(zram->comp);
 	}
 
 	alloced_pages = zs_get_total_pages(zram->mem_pool);
-- 
2.25.1

Re: [PATCH v2] zram: don't retry compress incompressible page

[Sergey Senozhatsky]

On (22/08/24 14:31), Alexey Romanov wrote:
> It doesn't make sense for us to retry to compress an uncompressible
> page (comp_len == PAGE_SIZE) in zsmalloc slowpath, because we will
> be storing it uncompressed anyway. We can avoid wasting time on
> another compression attempt. It is enough to take lock
> (zcomp_stream_get) and execute the code below.
> 
> Signed-off-by: Alexey Romanov <avromanov@sberdevices.ru>
> Signed-off-by: Dmitry Rokosov <ddrokosov@sberdevices.ru>

Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>