On Tue, May 06, 2014 at 09:28:07AM -0700, H. Peter Anvin wrote:

On 04/25/2014 01:10 AM, Cyrill Gorcunov wrote:

quoted

Tracking dirty status on 2 level pages requires very ugly macros
and taking into account how old the machines who can operate
without PAE mode only are, lets drop soft dirty tracker from
them for code simplicity (note I can't drop all the macros
from 2 level pages by now since _PAGE_BIT_PROTNONE and
_PAGE_BIT_FILE are still used even without tracker).

Linus proposed to completely rip off softdirty support on
x86-32 (even with PAE) and since for CRIU we're not planning
to support native x86-32 mode, lets do that.

(Softdirty tracker is relatively new feature which mostly used
 by CRIU so I don't expect if such API change would cause problems
 on userspace).

I have to wonder which one is more likely to actually matter on whatever
legacy 32-bit are going to remain.  This pretty much comes down to what
kind of advanced features are going to matter in deep embedded
applications in the future: checkpoint/restart or NUMA.  My guess is
that it is actually checkpoint/restart...

How much does it actually simplify to leave this feature in for PAE?  I
could care less about non-PAE... NX has pretty much killed that off cold.

At the current state -- not much I would say. Initially the idea was to
drop x86-32 and use page-soft-dirty-bit (ie 11) inside swap entries dropping
off page-swap-soft-dirty bit completely, this would simplify all the things
but eventually I realized that if I do so the number of maximum swap entries
will get more shrinked which is inacceptable I think.

Thus, currently (ie even with this patches) we can work on x86-32+PAE but
desided to drop x86-32 completely to simplify things in future.

Peter, deep embedded applications I guess would be working on systems
with really small amount of memory installed in a system I suppose and
I doubt if they would need c/r?

If we deside to leave x86-32+PAE then don't apply this patch, I will
need to update it, (The first patch is safe to apply anyway).

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