linux-kernel - Re: [PATCH] block, bfq: Reorder struct bfq_iocq_bfqq

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ac0e993a-3e6d-6616-ce6c-03f0aa2429da@huaweicloud.com>
Date: Mon, 4 Aug 2025 08:47:20 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Christophe JAILLET <christophe.jaillet@...adoo.fr>,
 Jens Axboe <axboe@...nel.dk>
Cc: linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
 linux-block@...r.kernel.org, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH] block, bfq: Reorder struct bfq_iocq_bfqq_data

在 2025/08/02 15:25, Christophe JAILLET 写道:
> The size of struct bfq_iocq_bfqq_data can be reduced by moving a few fields
> around.
> 
> On a x86_64, with allmodconfig, this shrinks the size from 144 to 128
> bytes.
> The main benefit is to reduce the size of struct bfq_io_cq from 1360 to
> 1232.
> 
> This structure is stored in a dedicated slab cache. So reducing its size
> improves cache usage.
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
> Compile tested only.
> 
> On my system, struct bfq_io_cq are stored in 8 pages slab. Each of these
> slabs hold 24 entries.
> 
> $ sudo cat /proc/slabinfo | grep bfq_io
> bfq_io_cq            378    384   1360   24    8 : tunables    0    0    0 : slabdata     16     16      0
> 
> With the new layout, we should store 26 entries.
> (8 * 4096 / 1232 = 26.60)
> ---
>   block/bfq-iosched.h | 10 +++++-----
>   1 file changed, 5 insertions(+), 5 deletions(-)
> 

LGTM
Reviewed-by: Yu Kuai <yukuai3@...wei.com>

> diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
> index 687a3a7ba784..0b4704932d72 100644
> --- a/block/bfq-iosched.h
> +++ b/block/bfq-iosched.h
> @@ -427,9 +427,6 @@ struct bfq_iocq_bfqq_data {
>   	 */
>   	bool saved_IO_bound;
>   
> -	u64 saved_io_start_time;
> -	u64 saved_tot_idle_time;
> -
>   	/*
>   	 * Same purpose as the previous fields for the values of the
>   	 * field keeping the queue's belonging to a large burst
> @@ -450,6 +447,9 @@ struct bfq_iocq_bfqq_data {
>   	 */
>   	unsigned int saved_weight;
>   
> +	u64 saved_io_start_time;
> +	u64 saved_tot_idle_time;
> +
>   	/*
>   	 * Similar to previous fields: save wr information.
>   	 */
> @@ -457,13 +457,13 @@ struct bfq_iocq_bfqq_data {
>   	unsigned long saved_last_wr_start_finish;
>   	unsigned long saved_service_from_wr;
>   	unsigned long saved_wr_start_at_switch_to_srt;
> -	unsigned int saved_wr_cur_max_time;
>   	struct bfq_ttime saved_ttime;
> +	unsigned int saved_wr_cur_max_time;
>   
>   	/* Save also injection state */
> -	u64 saved_last_serv_time_ns;
>   	unsigned int saved_inject_limit;
>   	unsigned long saved_decrease_time_jif;
> +	u64 saved_last_serv_time_ns;
>   
>   	/* candidate queue for a stable merge (due to close creation time) */
>   	struct bfq_queue *stable_merge_bfqq;
>