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

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Date:   Wed, 23 Oct 2019 11:56:43 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH 4/8] mm: vmscan: naming fixes: global_reclaim() and
 sane_reclaim()

On Wed, Oct 23, 2019 at 04:14:36PM +0200, Michal Hocko wrote:
> On Tue 22-10-19 10:47:59, 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.
> 
> I somehow never had problem with that but ...
> > 
> > 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. ]
> 
> ... this is a valid point.
> 
> > 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()".
> 
> I do have a stronger opinion on this one. sane_reclaim is really a
> terrible name. As you say the only thing this should really tell is
> whether writeback throttling is available so I would rather go with
> has_writeback_throttling() or writeba_throttling_{eabled,available}
> If you insist on having sane in the name then I won't object but it just
> raises a question whether we have some levels of throttling with a
> different level of sanity.

I mean, cgroup1 *does* have a method to not OOM due to pages under
writeback: wait_on_page_writeback() on each wb page on the LRU.

It's terrible, but it's a form of writeback throttling. That's what
the sane vs insane distinction is about, I guess: we do in fact have
throttling implementations with different levels of sanity.

> > Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> 
> Acked-by: Michal Hocko <mhocko@...e.com>

Thanks!