linux-kernel - Re: [PATCH 1/2] f2fs: set 4KB discard granularity by default

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Message-ID: <20180814041329.GB52730@jaegeuk-macbookpro.roam.corp.google.com>
Date:   Mon, 13 Aug 2018 21:13:29 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, chao@...nel.org
Subject: Re: [PATCH 1/2] f2fs: set 4KB discard granularity by default

On 08/10, Chao Yu wrote:
> Small granularity (size < 64K) fragmentation will cause f2fs suspending
> all pending discards, result in performance regression, so let's set
> 4KB discard granularity by default.
> 
> So that without fstrim, we also have the ability to avoid any performance
> regression caused by non-alignment mapping between fs and flash device.

This is why we added a sysfs entry. Why do we need to change the default
value every time?

> 
> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> ---
>  fs/f2fs/f2fs.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 58431b9bfd8f..273ffdaf4891 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -248,7 +248,7 @@ struct discard_entry {
>  };
>  
>  /* default discard granularity of inner discard thread, unit: block count */
> -#define DEFAULT_DISCARD_GRANULARITY		16
> +#define DEFAULT_DISCARD_GRANULARITY		1
>  
>  /* max discard pend list number */
>  #define MAX_PLIST_NUM		512
> -- 
> 2.18.0.rc1