Re: [PATCH] mm/ksm: introduce ksm_enabled for each processg

[CGEL <cgel.zte@gmail.com>]

On Thu, May 19, 2022 at 09:39:57AM +0200, Michal Hocko wrote:
> On Thu 19-05-22 06:35:03, CGEL wrote:
> > On Wed, May 18, 2022 at 02:14:28PM +0200, Michal Hocko wrote:
> > > On Wed 18-05-22 07:40:30, CGEL wrote:
> > > [...]
> > > > 2. process_madvise is still a kind of madvise. processs_madvise from
> > > > another process overrides the intention of origin app code ifself that
> > > > also calls madvise, which is unrecoverable. For example, if a process "A"
> > > > which madvises just one part of VMAs (not all) as MERGEABLE run on the OS
> > > > already, meanwhile, if another process which doesn't know the information
> > > > of "A" 's MERGEABLE areas, then call process_madvise to advise all VMAs of
> > > > "A" as MERGEABLE, the original MERGEABLE information of "A" calling madivse
> > > > is erasured permanently.
> > > 
> > > I do not really follow. How is this any different from an external
> > > process modifying the process wide policy via the proc or any other
> > > interface?
> > 
> > In this patch, you can see that we didn't modify the flag of any VMA of
> > the target process, which is different from process_madvise. So it is
> > easy to keep the original MERGEABLE information of the target process
> > when we turn back to the default state from the state "always".
> 
> This means that /proc/<pid>/smaps doesn't show the real state, right?

Maybe we can add extra information of KSM forcible state in /proc/<pid>/smaps
like THPeligible. 

Really, Michal, I think it again, 'process_ madvise' is really not good. In
addition to some shortcomings I said before, If new vmas of the target process
are created after the external process calls process_madvise(), then we have to
call `process_madvise()` on them again, over and over again, regularly, just like
Oleksandr said [1].

[1]: https://lore.kernel.org/lkml/1817008.tdWV9SEqCh@natalenko.name/


> 
> -- 
> Michal Hocko
> SUSE Labs