2022-04-26 11:28:19

by Yu Kuai

Subject: [PATCH] null-blk: save memory footprint for struct nullb_cmd

Total 16 bytes can be saved in two ways:

1) The field 'bio' will only be used in bio based mode, and the field
'rq' will only be used in mq mode. Since they won't be used in the
same time, declare a union for them.
2) The field 'bool fake_timeout' can be placed in the hole after the
field 'error'.

Signed-off-by: Yu Kuai <[email protected]>
---
drivers/block/null_blk/null_blk.h | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/block/null_blk/null_blk.h b/drivers/block/null_blk/null_blk.h
index 78eb56b0ca55..4525a65e1b23 100644
--- a/drivers/block/null_blk/null_blk.h
+++ b/drivers/block/null_blk/null_blk.h
@@ -16,13 +16,15 @@
#include <linux/mutex.h>

struct nullb_cmd {
- struct request *rq;
- struct bio *bio;
+ union {
+ struct request *rq;
+ struct bio *bio;
+ };
unsigned int tag;
blk_status_t error;
+ bool fake_timeout;
struct nullb_queue *nq;
struct hrtimer timer;
- bool fake_timeout;
};

struct nullb_queue {
--
2.31.1

2022-04-26 19:03:52

by Jens Axboe

Subject: Re: [PATCH] null-blk: save memory footprint for struct nullb_cmd

On Tue, 26 Apr 2022 10:21:33 +0800, Yu Kuai wrote:
> Total 16 bytes can be saved in two ways:
>
> 1) The field 'bio' will only be used in bio based mode, and the field
> 'rq' will only be used in mq mode. Since they won't be used in the
> same time, declare a union for them.
> 2) The field 'bool fake_timeout' can be placed in the hole after the
> field 'error'.
>
> [...]

Applied, thanks!

[1/1] null-blk: save memory footprint for struct nullb_cmd
commit: 8ba816b23abd2a9a05705f3d00b8653f8be73015

Best regards,
--
Jens Axboe