Re: dm-writecache

[Dan Williams <dan.j.williams@intel.com>]

On Fri, May 18, 2018 at 8:44 AM, Mike Snitzer <snitzer@redhat.com> wrote:
> On Thu, Mar 08 2018 at 12:08pm -0500,
> Dan Williams <dan.j.williams@intel.com> wrote:
>
>> Mikulas sent this useful enhancement to the memcpy_flushcache API:
>>
>>     https://patchwork.kernel.org/patch/10217655/
>>
>> ...it's in my queue to either push through -tip or add it to the next
>> libnvdimm pull request for 4.17-rc1.
>
> Hi Dan,
>
> Seems this never actually went upstream.  I've staged it in
> linux-dm.git's "for-next" for the time being:
> https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-4.18&id=a7e96990b5ff6206fefdc5bfe74396bb880f7e48
>
> But do you intend to pick it up for 4.18 inclusion?  If so I'll drop
> it.. would just hate for it to get dropped on the floor by getting lost
> in the shuffle between trees.
>
> Please avise, thanks!
> Mike

Thanks for picking it up! I was hoping to resend it to get acks from
x86 folks, and then yes it fell through the cracks in my patch
tracking.

Now that I look at it again I don't think we need this hunk:

void memcpy_page_flushcache(char *to, struct page *page, size_t offset,
size_t len)
{
char *from = kmap_atomic(page);
- memcpy_flushcache(to, from + offset, len);
+ __memcpy_flushcache(to, from + offset, len);
kunmap_atomic(from);
}

...and I wonder what the benefit is of the 16-byte case? I would
assume the bulk of the benefit is limited to the 4 and 8 byte copy
cases.

Mikulas please resend with those comments addressed and include Ingo and Thomas.
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