2022-08-24 11:46:50

by Alexey Romanov

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

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 <[email protected]>
Signed-off-by: Dmitry Rokosov <[email protected]>
---
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

2022-08-25 08:22:58

by Sergey Senozhatsky

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

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 <[email protected]>
> Signed-off-by: Dmitry Rokosov <[email protected]>

Reviewed-by: Sergey Senozhatsky <[email protected]>