Re: [PATCH 2/2] mm: replace remap_file_pages() syscall with emulation

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

On Thu, 15 May 2014 00:17:48 +0300 "Kirill A. Shutemov" <kirill@shutemov.name> wrote:

> On Wed, May 14, 2014 at 04:52:17PM -0400, Sasha Levin wrote:
> > On 05/12/2014 01:05 PM, Kirill A. Shutemov wrote:
> > > Taking into account your employment, is it possible to check how the RDBMS
> > > (old but it still supported 32-bit versions) would react on -ENOSYS here?
> > 
> > Alrighty, I got an answer:
> > 
> > 1. remap_file_pages() only works when the "VLM" feature of the db is enabled,
> > so those databases can work just fine without it, but be limited to 3-4GB of
> > memory. This is not needed at all on 64bit machines.
> 
> Okay. And it seems user need to enable it manually with option
> USE_INDIRECT_DATA_BUFFERS=TRUE.
> 
> http://docs.oracle.com/cd/B28359_01/server.111/b32009/appi_vlm.htm
> 
> > 2. As of OL7 (kernel 3.8), there will not be a 32bit kernel build. I'm still
> > waiting for an answer whether there will do a 32bit DB build for a 64bit kernel,
> > but that never happened before and seems unlikely.
> > 
> > 3. They're basically saying that by the time upstream releases a kernel without
> > remap_file_pages() no one will need it here.
> > 
> > To sum it up, they're fine with removing remap_file_pages().
> 
> Andrew, Linus, what will we do here: live with emulation or just kill the
> syscall? Or may be kill the syscall after few releases with emulation?

Well we can put the printk in there initially to gather more
information.

If it appears necessary then we can include the emulation, but retain
the "this-is-going-away" printk then remove the emulation later on.