Re: [xfs-masters] Re: freeze vs freezer

[Jeremy Fitzhardinge <jeremy@goop.org>]

Dave Chinner wrote:
> On Mon, Jun 30, 2008 at 01:22:47AM +0200, Rafael J. Wysocki wrote:
>   
>> On Monday, 30 of June 2008, Dave Chinner wrote:
>>     
>>> On Thu, Jun 26, 2008 at 05:09:10PM +0200, Pavel Machek wrote:
>>>       
>>>>>> Is this the same thing the per-device IO-queue-freeze patches for
>>>>>> HDAPS also
>>>>>> need to do?  If so, you may want to talk to Elias Oltmanns
>>>>>> <eo@nebensachen.de> about it.  Added to CC.
>>>>>>             
>>>>> Thanks for the heads up Henrique. Even though these issues seem to be
>>>>> related up to a certain degree, there probably are some important
>>>>> differences. When suspending a system, the emphasis is on leaving the
>>>>> system in a consistent state (think of journalled file systems), whereas
>>>>> disk shock protection is mainly concerned with stopping I/O as soon as
>>>>> possible. As yet, I cannot possibly say to what extend these two
>>>>> concepts can be reconciled in the sense of sharing some common code.
>>>>>           
>>>> Actually, I believe requirements are same.
>>>>
>>>> 'don't do i/o in dangerous period'.
>>>>
>>>> swsusp will just do sync() before entering dangerous period. That
>>>> provides consistent-enough state...
>>>>         
>>> As I've said many times before - if the requirement is "don't do
>>> I/O" then you have to freeze the filesystem. In no way does 'sync'
>>> prevent filesystems from doing I/O.....
>>>       
>> Well, it seems we can handle this on the block layer level, by temporarily
>> replacing the elevator with something that will selectively prevent fs I/O
>> from reaching the layers below it.
>>     
>
> Why? What part of freeze_bdev() doesn't work for you?

Well, my original problem - which is still an issue - is that a process 
writing to a frozen XFS filesystem is stuck in D state, and therefore 
cannot be frozen as part of suspend.

    J