Re: [PATCH] mm: fix draining remote pageset

[Lameter, Christopher]

On Wed, 16 Aug 2023, Huang, Ying wrote:

> Michal Hocko <mhocko@xxxxxxxx> writes:
> > > > Why is that a problem?
> > >
> > > The pages of the remote zone may be kept in the local per-CPU pageset
> > > for long time as long as there's no page allocation/freeing on the
> > > logical CPU.  In addition to the logical CPU goes idle, this is also
> > > possible if the logical CPU is busy in the user space.
> >
> > But why is this a problem? Is the scale of the problem sufficient to
> > trigger out of memory situations or be otherwise harmful?
>
> This may trigger premature page reclaiming.  The pages in the PCP of the
> remote zone would have been freed to satisfy the page allocation for the
> remote zone to avoid page reclaiming.  It's highly possible that the
> local CPU just allocate/free from/to the remote zone temporarily.  So,
> we should free PCP pages of the remote zone if there is no page
> allocation/freeing from/to the remote zone for 3 seconds.
>
> This will not trigger OOM, because all PCP will be drained if allocation
> failed after direct reclaiming.

I think this is a minor issue but its cleaner behavior. 
vmstat refresh's should continue as long as there are 
pages queued in remote pcps.