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

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Date:   Wed, 6 Jan 2021 09:15:53 +0800
From:   "Li, Hao" <lihao2018.fnst@...fujitsu.com>
To:     Ira Weiny <ira.weiny@...el.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] Documentation/dax: Update description of DAX policy
 changing

On 2021/1/5 0:36, Ira Weiny wrote:
> On Mon, Jan 04, 2021 at 10:40:40AM +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>
>> ---
>>  Documentation/filesystems/dax.txt | 15 ++-------------
>>  1 file changed, 2 insertions(+), 13 deletions(-)
>>
>> diff --git a/Documentation/filesystems/dax.txt b/Documentation/filesystems/dax.txt
>> index 8fdb78f3c6c9..a5af22831087 100644
>> --- a/Documentation/filesystems/dax.txt
>> +++ b/Documentation/filesystems/dax.txt
>> @@ -84,19 +84,8 @@ Summary
>>         described in 6) below.
>>  
>>   6. When changing the S_DAX policy via toggling the persistent FS_XFLAG_DAX flag,
>                                                                                   ^^
>                                                   I would delete this '.' as well.
>
>> -    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
>> +    the change to existing regular file won't take effect until the file is closed
>                                                                       ^^^^^
>                                                                       files
>
>> +    by all processes or all processes referencing the file are stopped.
>
> So how about:
>
>    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 file
>       is closed by all processes or all processes referencing the file are
>       stopped.
>
> I also feel like mentioning the stoppage of process' is redundant as users
> should know that will result in the closing of those FDs but I'm ok leaving it
> if others like it.

Thanks, it's much better than before.

Regards,
Hao Li

>
>
> Ira
>
>>  
>>  
>>  Details
>> --
>> 2.29.2
>>
>>
>>
>
>