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Subject: Re: staging: ion: ION allocation fall back order depends on heap
 linkage order
To:     Alexey Skidanov <alexey.skidanov@intel.com>,
        devel@driverdev.osuosl.org
Cc:     linux-kernel@vger.kernel.org
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 <0217ee91-25fa-f563-81bd-ba4ad4dc9377@intel.com>
From:   Laura Abbott <labbott@redhat.com>
Message-ID: <a210baff-4124-b0d7-bcd9-a2ee8b986c7a@redhat.com>
Date:   Wed, 7 Feb 2018 06:58:36 -0800
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On 02/06/2018 11:05 PM, Alexey Skidanov wrote:
> 
> 
>> Yup, you've hit upon a key problem. Having fallbacks be stable
>> was always a problem and the recommendation these days is to
>> not rely on them. You can specify a heap at a time and fallback
>> manually if you want that behavior.
>>
>> If you have a proposal to make fallbacks work reliably without
>> overly complicating the ABI I'm happy to review it.
>>
>> Thanks,
>> Laura
>>
> I think it's possible to "automate" the "manual fallback" behavior. But
> the real issues is using heap id to specify the particular heap object.
> 
> Current API (allocation IOCTL) requires to specify the particular heap
> object by using heap id. From the other hand, the user space doesn't
> control the heaps creation order and heap id assignment. So it may be
> tricky, especially when more than one object of the same heap type is
> created automatically.
> 
> Thanks,
> Alexey
> 
> 

The query ioctl is designed to get the heap ID information without
needing to rely on the linking order or anything else defined in
the kernel.

Thanks,
Laura