Re: [PATCH] pmem: export the symbols __copy_user_flushcache and __copy_from_user_flushcache

[Mikulas Patocka]

On Wed, 16 Sep 2020, Dan Williams wrote:

> On Wed, Sep 16, 2020 at 3:57 AM Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote:
> >
> >
> >
> > I'm submitting this patch that adds the required exports (so that we could
> > use __copy_from_user_flushcache on x86, arm64 and powerpc). Please, queue
> > it for the next merge window.
> 
> Why? This should go with the first user, and it's not clear that it
> needs to be relative to the current dax_operations export scheme.

Before nvfs gets included in the kernel, I need to distribute it as a 
module. So, it would make my maintenance easier. But if you don't want to 
export it now, no problem, I can just copy __copy_user_flushcache from the 
kernel to the module.

> My first question about nvfs is how it compares to a daxfs with
> executables and other binaries configured to use page cache with the
> new per-file dax facility?

nvfs is faster than dax-based filesystems on metadata-heavy operations 
because it doesn't have the overhead of the buffer cache and bios. See 
this: http://people.redhat.com/~mpatocka/nvfs/BENCHMARKS

Mikulas