Re: [PATCH v4] mm: introduce reference pages

[John Hubbard <jhubbard@nvidia.com>]

On 6/28/21 12:33 PM, Matthew Wilcox wrote:
...
> 
> I wonder if single-byte captures enough of the useful possibilities.
> In the kernel we have memset32() and memset64() [1] so we could support
> a larger pattern than just an 8-bit byte.  It all depends what userspace
> would find useful.
> 
> [1] Along with memset_p(), memset_l() and memset16() that aren't terribly
> relevant to this use case.  Although maybe memset_l() would be the right
> one to use since there probably aren't too many 32-bit apps that want
> a 64-bit pattern and memset64() might not be the fastest on a 32-bit
> kernel).
> 

And in fact, I'm also rather intrigued by doing something like 256 copies
of a 16-byte UUID, per 4KB page. In other words, there are *definitely*
useful patterns that are longer than a single byte, and it seems interesting
to support them here.

Kirill's idea of an API that somehow allows various power of 2 patterns seems
like it would be nice, because then we don't have to pick a value that seems
good in 2021, but less good as time goes by, perhaps.

Another thought is to use an entire 4KB page as the smallest pattern unit.
That would allow the maximum API flexibility, because the caller could
explicitly set every single byte in the page.


thanks,
-- 
John Hubbard
NVIDIA