linux-kernel - Re: [PATCH 4/4] workqueue: slash half memory usage in 32bit system

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Message-ID: <20200601150723.GA31548@mtj.thefacebook.com>
Date:   Mon, 1 Jun 2020 11:07:23 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Lai Jiangshan <laijs@...ux.alibaba.com>
Cc:     linux-kernel@...r.kernel.org,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [PATCH 4/4] workqueue: slash half memory usage in 32bit system

On Mon, Jun 01, 2020 at 08:44:42AM +0000, Lai Jiangshan wrote:
> The major memory ussage in workqueue is on the pool_workqueue.
> The pool_workqueue has alignment requirement which often leads
> to padding.
> 
> Reducing the memory usage for the pool_workqueue is valuable.
> 
> And 32bit system often has less memory, less workqueues,
> less works, less concurrent flush_workqueue()s, so we can
> slash the flush color on 32bit system to reduce memory usage
> 
> Before patch:
> The sizeof the struct pool_workqueue is 256 bytes,
> only 136 bytes is in use in 32bit system
> 
> After patch:
> The sizeof the struct pool_workqueue is 128 bytes,
> only 104 bytes is in use in 32bit system, there is still
> room for future usage.
> 
> Setting WORK_STRUCT_COLOR_BITS to 3 can't reduce the sizeof
> the struct pool_workqueue in 64bit system, unless combined
> with big refactor for unbound pwq.

Have you calculated how much memory is actually saved this way on a typical
system?

Thanks.

-- 
tejun