Re: [RFC, PATCH 0/8] remap_file_pages() decommission

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 7 May 2014 11:12:58 +0200 Peter Zijlstra <peterz@infradead.org> wrote:

> On Tue, May 06, 2014 at 04:28:56PM -0700, Andrew Morton wrote:
> > On Wed, 7 May 2014 02:03:23 +0300 "Kirill A. Shutemov" <kirill@shutemov.name> wrote:
> > 
> > > remap_file_pages(2) was invented to be able efficiently map parts of
> > > huge file into limited 32-bit virtual address space such as in database
> > > workloads.
> > > 
> > > Nonlinear mappings are pain to support and it seems there's no
> > > legitimate use-cases nowadays since 64-bit systems are widely available.
> > > 
> > > Let's deprecate remap_file_pages() syscall in hope to get rid of code
> > > one day.
> > 
> > Before we do this we should ensure that your proposed replacement is viable
> > and desirable.  If we later decide not to proceed with it, this patch will
> > sow confusion.
> 
> Chicken meet Egg ?
> 
> How are we supposed to test if its viable if we have no known users?

Same way we always do - finish the code, developer test, review, give
it a spin in linux-next, etc.  Do some microbenchmarking to get an
understanding of the impact on people who are using r_f_p for real. 
The current patchset looks rather alphaish.

> The
> printk() might maybe (hopefully) get us some reaction in say a years
> time, much longer if we're really unlucky.
> 
> That said, we could make the syscall return -ENOSYS unless a sysctl was
> touched. The printk() would indeed have to mention said sysctl and a
> place to find information about why we're doing this..
> 
> But by creating more pain (people have to actually set the sysctl, and
> we'll have to universally agree to inflict pain on distro people that
> set it by default -- say, starve them from beer at the next conf.) we're
> more likely to get an answer sooner.

Could be.  We should consult distro people, Oracle people...

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>