[dm-devel] [patch 4/4] dm-writecache: use new API for flushing

[Dan Williams]

On Thu, May 31, 2018 at 1:19 AM, Mikulas Patocka <mpatocka at redhat.com> wrote:
>
>
> On Wed, 30 May 2018, Dan Williams wrote:
>
>> > Great find! Thanks for the due diligence. Feel free to add:
>> >
>> >     Acked-by: Dan Williams <dan.j.williams at intel.com>
>> >
>> > ...on the reworks to unify ARM and x86.
>>
>> One more note. The side effect of not using dax_flush() is that you
>> may end up flushing caches on systems where the platform has asserted
>> it will take responsibility for flushing caches at power loss. If /
>> when those systems become more prevalent we may want to think of a way
>> to combine the non-temporal optimization and the cache-flush-bypass
>> optimizations. However that is something that can wait for a later
>> change beyond 4.18.
>
> We could define memcpy_flushpmem, that falls back to memcpy or
> memcpy_flushcache, depending on whether the platform flushes the caches at
> power loss or not.

The problem is that some platforms only power fail protect a subset of
the physical address range, but yes, if the platform makes a global
assertion we can globally replace memcpy_flushpmem() with plain
memcpy.