Re: [PATCH 5/5] mm: Soft-dirty bits for user memory changes tracking

[Pavel Emelyanov <xemul@parallels.com>]

>>> >From that perspective, the dependency on X86 is awful.  What's the
>>> problem here and what do other architectures need to do to be able to
>>> support the feature?
>>
>> The problem here is that I don't know what free bits are available on
>> page table entries on other architectures. I was about to resolve this
>> for ARM very soon, but for the rest of them I need help from other people.
> 
> Well, this is also a thing arch maintainers can do when they feel a
> need to support the feature on their architecture.  To support them at
> that time we should provide them with a) adequate information in an
> easy-to-find place (eg, a nice comment at the site of the reference x86
> implementation) and b) a userspace test app.

Item a) is presumably covered with two things -- required arch-specific
PTE manipulations are all collected in asm-generic/pgtable.h under the
!CONFIG_HAVE_ARCH_SOFT_DIRTY and the Documentation/vm/soft-dirty.txt
pointed by the API clear_refs_soft_dirty()'s comment.

Item b) was recently merged.

Item c) from Stephen is already sent.

Thank you for your time and help,
Pavel

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