svn commit: r364129 - head/sys/vm

[Conrad Meyer]

Done in r364134.

On Tue, Aug 11, 2020 at 3:31 PM Mark Johnston <markj at freebsd.org> wrote:
>
> On Tue, Aug 11, 2020 at 03:21:31PM -0700, Conrad Meyer wrote:
> > Hi Konstantin, Mark (raised the same question),
> >
> > On Tue, Aug 11, 2020 at 2:32 PM Konstantin Belousov <kostikbel at gmail.com> wrote:
> > >
> > > On Tue, Aug 11, 2020 at 08:37:45PM +0000, Conrad Meyer wrote:
> > > > Author: cem
> > > > Date: Tue Aug 11 20:37:45 2020
> > > > New Revision: 364129
> > > > URL: https://svnweb.freebsd.org/changeset/base/364129
> > > >
> > > > Log:
> > > >   Add support for multithreading the inactive queue pageout within a domain.
> > > > ...
> > > > @@ -2488,7 +2488,7 @@ vm_page_zone_import(void *arg, void **store, int cnt,
> > > >        * main purpose is to replenish the store of free pages.
> > > >        */
> > > >       if (vmd->vmd_severeset || curproc == pageproc ||
> > > > -         !_vm_domain_allocate(vmd, VM_ALLOC_NORMAL, cnt))
> > > > +         !_vm_domain_allocate(vmd, VM_ALLOC_SYSTEM, cnt))
> > >
> > > Why this change needed ?
> >
> > The change was inherited from Jeff, along with the rest of it.  I
> > don't know why he changed it, but it does seem orthogonal to the rest
> > of the revision.  This part is nonessential as far as I know, and
> > could be backed out.
>
> To me it doesn't make sense.  The difference between VM_ALLOC_NORMAL and
> _SYSTEM is that they use different thresholds for the free page count
> before deciding whether to continue the allocation.  The _NORMAL
> threshold is higher than the _SYSTEM threshold, but both are smaller
> than the "severe" threshold at which we set vmd_severeset.  In other
> words, if the free page count is such that a _NORMAL allocation would
> fail but a _SYSTEM allocation would succeed, then vmd_severeset would be
> set and we'd never get to the _vmd_domain_allocate() call to begin with.
>
> So, I think this part of the change should be reverted.  Even if the
> analysis is incorrect, it's logically separate from the rest of the
> diff.  Prior to r355003 it made more sense, but per that commit it can
> be harmful to populate the per-CPU page caches when the system is
> severely short on free pages, so I would disagree with it anyway without
> more testing.