Re: [RFC v2 PATCH 2/8] mm: introduce MIGRATE_MIRROR to manage the mirrored pages

[Xishi Qiu]

On 2015/6/29 15:32, Kamezawa Hiroyuki wrote:

> On 2015/06/27 11:24, Xishi Qiu wrote:
>> This patch introduces a new migratetype called "MIGRATE_MIRROR", it is used to
>> allocate mirrored pages.
>> When cat /proc/pagetypeinfo, you can see the count of free mirrored blocks.
>>
>> Signed-off-by: Xishi Qiu <qiuxishi@xxxxxxxxxx>
> 
> My fear about this approarch is that this may break something existing.
> 
> Now, when we add MIGRATE_MIRROR type, we'll hide attributes of pageblocks as
> MIGRATE_UNMOVABOLE, MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE.
> 
> Logically, MIRROR attribute is independent from page mobility and this overwrites
> will make some information lost.
> 
> Then,
> 
>> ---
>>   include/linux/mmzone.h | 9 +++++++++
>>   mm/page_alloc.c        | 3 +++
>>   mm/vmstat.c            | 3 +++
>>   3 files changed, 15 insertions(+)
>>
>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
>> index 54d74f6..54e891a 100644
>> --- a/include/linux/mmzone.h
>> +++ b/include/linux/mmzone.h
>> @@ -39,6 +39,9 @@ enum {
>>       MIGRATE_UNMOVABLE,
>>       MIGRATE_RECLAIMABLE,
>>       MIGRATE_MOVABLE,
>> +#ifdef CONFIG_MEMORY_MIRROR
>> +    MIGRATE_MIRROR,
>> +#endif
> 
> I think
>         MIGRATE_MIRROR_UNMOVABLE,
>         MIGRATE_MIRROR_RECLAIMABLE,
>         MIGRATE_MIRROR_MOVABLE,         <== adding this may need discuss.
>         MIGRATE_MIRROR_RESERVED,        <== reserved pages should be maintained per mirrored/unmirrored.
> 

Hi Kame,

You mean add 3 or 4 new migratetype?

> should be added with the following fallback list.
> 
> /*
>  * MIRROR page range is defined by firmware at boot. The range is limited
>  * and is used only for kernel memory mirroring.
>  */
> [MIGRATE_UNMOVABLE_MIRROR]   = {MIGRATE_RECLAIMABLE_MIRROR, MIGRATE_RESERVE}
> [MIGRATE_RECLAIMABLE_MIRROR] = {MIGRATE_UNMOVABLE_MIRROR, MIGRATE_RESERVE}
> 

Why not like this:
{MIGRATE_RECLAIMABLE_MIRROR, MIGRATE_MIRROR_RESERVED, MIGRATE_RESERVE}

> Then, we'll not lose the original information of "Reclaiable Pages".
> 
> One problem here is whteher we should have MIGRATE_RESERVE_MIRROR.
> 
> If we never allow users to allocate mirrored memory, we should have MIGRATE_RESERVE_MIRROR.
> But it seems to require much more code change to do that.
> 
> Creating a zone or adding an attribues to zones are another design choice.
> 

If we add a new zone, mirror_zone will span others, I'm worry about this
maybe have problems.

Thanks,
Xishi Qiu

> Anyway, your patch doesn't takes care of reserved memory calculation at this point.
> Please check setup_zone_migrate_reserve() That will be a problem.
> 
> Thanks,
> -Kame
> 



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