Re: [PATCH 2/9] mm: workingset: tell cache transitions from workingset thrashing

[Johannes Weiner]

Hi Suren,

On Wed, Aug 01, 2018 at 02:56:27PM -0700, Suren Baghdasaryan wrote:
> On Wed, Aug 1, 2018 at 8:19 AM, Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
> >         /*
> > -        * The unsigned subtraction here gives an accurate distance
> > -        * across inactive_age overflows in most cases.
> > +        * Calculate the refault distance
> >          *
> > -        * There is a special case: usually, shadow entries have a
> > -        * short lifetime and are either refaulted or reclaimed along
> > -        * with the inode before they get too old.  But it is not
> > -        * impossible for the inactive_age to lap a shadow entry in
> > -        * the field, which can then can result in a false small
> > -        * refault distance, leading to a false activation should this
> > -        * old entry actually refault again.  However, earlier kernels
> > -        * used to deactivate unconditionally with *every* reclaim
> > -        * invocation for the longest time, so the occasional
> > -        * inappropriate activation leading to pressure on the active
> > -        * list is not a problem.
> > +        * The unsigned subtraction here gives an accurate distance
> > +        * across inactive_age overflows in most cases. There is a
> > +        * special case: usually, shadow entries have a short lifetime
> > +        * and are either refaulted or reclaimed along with the inode
> > +        * before they get too old.  But it is not impossible for the
> > +        * inactive_age to lap a shadow entry in the field, which can
> > +        * then can result in a false small refault distance, leading
> 
> "which can then can" - please remove one of the "can".

Good catch, will fix.