linux-kernel - Re: [PATCH v2] Documentation/dax: Update description of DAX policy changing

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Date:   Tue, 5 Jan 2021 21:45:41 -0800
From:   Ira Weiny <ira.weiny@...el.com>
To:     Hao Li <lihao2018.fnst@...fujitsu.com>
Cc:     corbet@....net, davem@...emloft.net, gregkh@...uxfoundation.org,
        alexander.deucher@....com, mchehab+huawei@...nel.org,
        lee.jones@...aro.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] Documentation/dax: Update description of DAX policy
 changing

On Wed, Jan 06, 2021 at 09:50:00AM +0800, Hao Li wrote:
> After commit 77573fa310d9 ("fs: Kill DCACHE_DONTCACHE dentry even if
> DCACHE_REFERENCED is set"), changes to DAX policy will take effect
> as soon as all references to this file are gone.
> 
> Update the documentation accordingly.
> 
> Signed-off-by: Hao Li <lihao2018.fnst@...fujitsu.com>

LGTM

Reviewed-by: Ira Weiny <ira.weiny@...el.com>

> ---
> Changes in v2:
>   * simplify sentences and fix style problems.
> 
>  Documentation/filesystems/dax.txt | 17 +++--------------
>  1 file changed, 3 insertions(+), 14 deletions(-)
> 
> diff --git a/Documentation/filesystems/dax.txt b/Documentation/filesystems/dax.txt
> index 8fdb78f3c6c9..e03c20564f3a 100644
> --- a/Documentation/filesystems/dax.txt
> +++ b/Documentation/filesystems/dax.txt
> @@ -83,20 +83,9 @@ Summary
>         directories.  This has runtime constraints and limitations that are
>         described in 6) below.
>  
> - 6. When changing the S_DAX policy via toggling the persistent FS_XFLAG_DAX flag,
> -    the change in behaviour for existing regular files may not occur
> -    immediately.  If the change must take effect immediately, the administrator
> -    needs to:
> -
> -    a) stop the application so there are no active references to the data set
> -       the policy change will affect
> -
> -    b) evict the data set from kernel caches so it will be re-instantiated when
> -       the application is restarted. This can be achieved by:
> -
> -       i. drop-caches
> -       ii. a filesystem unmount and mount cycle
> -       iii. a system reboot
> + 6. When changing the S_DAX policy via toggling the persistent FS_XFLAG_DAX
> +    flag, the change to existing regular files won't take effect until the
> +    files are closed by all processes.
>  
>  
>  Details
> -- 
> 2.29.2
> 
> 
>