linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: make gc

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Date:   Tue, 25 Oct 2022 10:51:33 +0800
From:   Chao Yu <chao@...nel.org>
To:     Yangtao Li <frank.li@...o.com>, jaegeuk@...nel.org
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [f2fs-dev] [PATCH] f2fs: make gc_idle sysfs node readable

On 2022/10/25 10:33, Yangtao Li wrote:
> Hi Chao,
> 
> What:       /sys/fs/f2fs/<disk>/gc_idle
> Date:       July 2013
> Contact:    "Namjae Jeon" <namjae.jeon@...sung.com>
> Description:    Controls the victim selection policy for garbage collection.
>          Setting gc_idle = 0(default) will disable this option. Setting:
> 
>          ===========  ===============================================
>          gc_idle = 1  will select the Cost Benefit approach & setting
>          gc_idle = 2  will select the greedy approach & setting
>          gc_idle = 3  will select the age-threshold based approach.
>          ===========  ===============================================
> 
>  From the kernel documentation, this node only describes the writing of
> the value, and does not describe the reading of the value.

  If the value is used by userspace program, after the change, it will break
userspace.

> 
> Actually, this modification does the same thing as commit e60aeb2dee1a
> ("f2fs: make gc_urgent and gc_segment_mode sysfs node readabl").
> I understand it is an addition to the omission of the patch above.
> 
> Why gc_urgent and gc_segment_mode can be modified to string, but gc_idle
> breaks forward compatibility?

Oops, I guess that patch may have caused a regression...if there is any
user..

> 
> Thanks,