Re: [PATCH 2/2] x86: use pv-ops in {pte,pmd}_{set,clear}_flags()

[Cyrill Gorcunov <gorcunov@gmail.com>]

On Wed, Apr 02, 2014 at 03:33:48PM +0400, Pavel Emelyanov wrote:
...
> >>
> >> But you'd have to be insane to care about NUMA balancing on 32-bit,
> >> even with PAE. So restricting it to x86-64 and using the high bits (I
> >> think bits 52-62 are all available to SW) sounds fine to me.
> >>
> >> Same goes for soft-dirty. I think it's fine if we say that you won't
> >> have soft-dirty with a 32-bit kernel. Even with PAE.
> > 
> > Well, at the moment we use soft-dirty for x86-64 only in criu but there
> > were plans to implement complete 32bit support as well. While personally
> > I don't mind dropping soft-dirty for non x86-64 case, I would like
> > to hear Pavel's opinion, Pavel?
> 
> We (Parallels) don't have plans on C/R on 32-bit kernels, but I speak only
> for Parallels. However, people I know who need 32-bit C/R use ARM :)

OK, since it's x86 specific I can prepare patch for dropping softdirty on
x86-32 (this will release ugly macros in file mapping a bit but not that
significantly).

Guys, while looking into how to re-define _PAGE bits for case where present
bit is dropped I though about the form like

#define _PAGE_BIT_FILE		(_PAGE_BIT_PRESENT + 1)	/* _PAGE_BIT_RW */
#define _PAGE_BIT_NUMA		(_PAGE_BIT_PRESENT + 2)	/* _PAGE_BIT_USER */
#define _PAGE_BIT_PROTNONE	(_PAGE_BIT_PRESENT + 3)	/* _PAGE_BIT_PWT */

and while _PAGE_BIT_FILE case should work (as well as swap pages), I'm not that
sure about the numa and protnone case. I fear there are some code paths which
depends on the former bits positions -- ie when

	PAGE_BIT_PROTNONE = _PAGE_BIT_NUMA = _PAGE_BIT_GLOBAL.

One of the _PAGE_BIT_GLOBAL user is the page attributes code. It seems to always check
_PAGE_BIT_PRESENT together with _PAGE_BIT_GLOBAL, so if _PAGE_BIT_PROTNONE get redefined
to a new value it should not fail. Thus main concern is protnone + numa code, which
I must admit I don't know well enough yet.

--
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>