On Mon, May 09, 2022 at 04:40:50PM +0100, Matthew Wilcox wrote:
> On Mon, May 09, 2022 at 06:57:33AM +0000, CGEL wrote:
> > On Sun, May 08, 2022 at 07:03:36PM +0100, Matthew Wilcox wrote:
> > > On Sun, May 08, 2022 at 09:27:10AM +0000, cgel.zte@xxxxxxxxx wrote:
> > > > If ksm_force is set to 0, cancel the feature of ksm_force of this
> > > > process and unmerge those merged pages belonging to VMAs which is not
> > > > madvised as MADV_MERGEABLE of this process, but leave MADV_MERGEABLE
> > > > areas merged.
> > >
> > > Is that actually a useful feature? Otherwise, we could simply turn
> > > on/off the existing MMF_VM_MERGEABLE flag instead of introducing this
> > > new bool.
> > >
> > I think this will be very useful for those apps which are very likely to
> > cause Same Pages in memory and users and operators are not willing to
> > modified the source codes for any reasons.
>
> No, you misunderstand. Is it useful to have the "force KSM off"
> functionality? ie code which has been modified to allow KSM, but
> then overridden by an admin?
>
Oh, I see what you mean. It should be mentioned that "force KSM off" is not
implemented for the current patch. In this patch, setting ksm_force to 0 just
restores the system to the default state (the state before patching)
> > Besides, simply turning of/off the existing MMF_VM_MERGEABLE flag may be
> > not feasible because madvise will also turn on the MMF_VM_MERGEABLE
> > flag.
> >
> > I think the following suggestions is good, and I will resend a patch.
> > > > +Controlling KSM with procfs
> > > > +===========================
> > > > +
> > > > +KSM can also operate on anonymous areas of address space of those processes's
> > > > +knob ``/proc/<pid>/ksm_force`` is on, even if app codes doesn't call madvise()
> > > > +explicitly to advise specific areas as MADV_MERGEABLE.
> > > > +
> > > > +You can set ksm_force to 1 to force all anonymous and qualified VMAs of
> > > > +this process to be involved in KSM scanning. But It is effective only when the
> > > > +klob of ``/sys/kernel/mm/ksm/run`` is set as 1.
> > >
> > > I think that last sentence doesn't really add any value.
> > >
> > > > + memset(buffer, 0, sizeof(buffer));
> > > > + if (count > sizeof(buffer) - 1)
> > > > + count = sizeof(buffer) - 1;
> > > > + if (copy_from_user(buffer, buf, count)) {
> > > > + err = -EFAULT;
> > > > + goto out_return;
> > >
> > > This feels a bit unnecessary. Just 'return -EFAULT' here.
> > >
> > > > + }
> > > > +
> > > > + err = kstrtoint(strstrip(buffer), 0, &force);
> > > > +
> > > > + if (err)
> > > > + goto out_return;
> > >
> > > 'return err'
> > >
> > > > + if (force != 0 && force != 1) {
> > > > + err = -EINVAL;
> > > > + goto out_return;
> > >
> > > 'return -EINVAL'
> > >
> > > > + }
> > > > +
> > > > + task = get_proc_task(file_inode(file));
> > > > + if (!task) {
> > > > + err = -ESRCH;
> > > > + goto out_return;
> > >
> > > 'return -ESRCH'
