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Subject: Re: staging: ion: ION allocation fall back order depends on heap
 linkage order
To:     Laura Abbott <labbott@redhat.com>, devel@driverdev.osuosl.org
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 <CAM7Y4U_hw5anfgGyAK2uVxOxA3zPoJtOa93mrw8k7xfyOaSTUA@mail.gmail.com>
From:   Alexey Skidanov <alexey.skidanov@intel.com>
Cc:     linux-kernel@vger.kernel.org
Message-ID: <0217ee91-25fa-f563-81bd-ba4ad4dc9377@intel.com>
Date:   Wed, 7 Feb 2018 09:05:22 +0200
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> 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