linux-kernel - Re: [PATCH 4/8] mm: vmscan: naming fixes: global_reclaim() and sane

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Date:   Wed, 23 Oct 2019 12:02:03 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Roman Gushchin <guro@...com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH 4/8] mm: vmscan: naming fixes: global_reclaim() and
 sane_reclaim()

On Tue, Oct 22, 2019 at 07:40:52PM +0000, Roman Gushchin wrote:
> On Tue, Oct 22, 2019 at 10:47:59AM -0400, Johannes Weiner wrote:
> > Seven years after introducing the global_reclaim() function, I still
> > have to double take when reading a callsite. I don't know how others
> > do it, this is a terrible name.
> > 
> > Invert the meaning and rename it to cgroup_reclaim().
> > 
> > [ After all, "global reclaim" is just regular reclaim invoked from the
> >   page allocator. It's reclaim on behalf of a cgroup limit that is a
> >   special case of reclaim, and should be explicit - not the reverse. ]
> > 
> > sane_reclaim() isn't very descriptive either: it tests whether we can
> > use the regular writeback throttling - available during regular page
> > reclaim or cgroup2 limit reclaim - or need to use the broken
> > wait_on_page_writeback() method. Use "writeback_throttling_sane()".
> > 
> > Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> > ---
> >  mm/vmscan.c | 38 ++++++++++++++++++--------------------
> >  1 file changed, 18 insertions(+), 20 deletions(-)
> > 
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 622b77488144..302dad112f75 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -239,13 +239,13 @@ static void unregister_memcg_shrinker(struct shrinker *shrinker)
> >  	up_write(&shrinker_rwsem);
> >  }
> >  
> > -static bool global_reclaim(struct scan_control *sc)
> > +static bool cgroup_reclaim(struct scan_control *sc)
> >  {
> > -	return !sc->target_mem_cgroup;
> > +	return sc->target_mem_cgroup;
> >  }
> 
> Isn't targeted_reclaim() better?
> 
> cgroup_reclaim() is also ok to me, but it sounds a bit like we reclaim
> from this specific cgroup. Also targeted/global is IMO a better opposition
> than cgroup/global (the latter reminds me days when there were global
> and cgroup LRUs).

I think "targeted" is quite a bit less descriptive when you come at
the page replacement algorithm without cgroups in mind.

> The rest of the patch looks good!
> 
> Reviewed-by: Roman Gushchin <guro@...com>

Thanks!