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SubjectRe: [linux-pm] Re: Hibernation considerations
On Fri, 20 Jul 2007, Jim Crilly wrote:

>>> has
>>> requested the image to be not greater than 50% of RAM. In that case you
>>> have
>>> to free some memory _before_ identifying memory to save and you must not
>>> race with applications that attempt to allocate memory while you're doing
>>> it.
>>
>> I disagree a little bit.
>>
>> first off, only the suspending kernel can know what can be freed and what
>> is needed to do so (remember this is kernel internals, it can change from
>> patch to patch, let alone version to version)
>>
>> second, if you have a lot of memory to free, and you can't just throw away
>> caches to do so, you don't know what is going to be involved in freeing
>> the memory, it's very possilbe that it is going to involve userspace, so
>> you can't freeze any significant portion of the system, so you can't
>> eliminate all chance of races
>>
>> what you can do is
>>
>> 1. try to free stuff
>> 2. stop the system and account for memory, is enough free
>> if not goto 1
>>
>> if userspace is dirtying memory fast enough, or is just useing enough
>> memory that you can't meet your limit you just won't be able to suspend.
>>
>> but under any other conditions you will eventually get enough memory free.
>>
>> so try several times and if you still fail tell the user they have too
>> much stuff running and they need to kill something.
>
> Which would be a pretty big regression from what we have now. With the
> current implementation I can hibernate under virtually any workload because
> the freezer stops everything and there's no competition for resources.

as long as what you are trying to save is <=50% of ram (at least with some
implementations). if you are trying to save more then 50% of ram with some
current implmenetations you just can't

David Lang
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