linux-kernel - Re: [PATCH v6 01/19] mm: memcg: factor out memcg- and lruvec-level changes out of __mod_lruvec

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Message-ID: <20200617025014.GB10812@carbon.lan>
Date:   Tue, 16 Jun 2020 19:50:14 -0700
From:   Roman Gushchin <guro@...com>
To:     Shakeel Butt <shakeelb@...gle.com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Linux MM <linux-mm@...ck.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Kernel Team <kernel-team@...com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 01/19] mm: memcg: factor out memcg- and lruvec-level
 changes out of __mod_lruvec_state()

On Tue, Jun 16, 2020 at 06:52:09PM -0700, Shakeel Butt wrote:
> On Mon, Jun 8, 2020 at 4:07 PM Roman Gushchin <guro@...com> wrote:
> >
> > To convert memcg and lruvec slab counters to bytes there must be
> > a way to change these counters without touching node counters.
> > Factor out __mod_memcg_lruvec_state() out of __mod_lruvec_state().
> >
> > Signed-off-by: Roman Gushchin <guro@...com>
> > Acked-by: Johannes Weiner <hannes@...xchg.org>
> > Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
> > ---
> >  include/linux/memcontrol.h | 17 +++++++++++++++
> >  mm/memcontrol.c            | 43 +++++++++++++++++++++-----------------
> >  2 files changed, 41 insertions(+), 19 deletions(-)
> >
> > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> > index bbf624a7f5a6..93dbc7f9d8b8 100644
> > --- a/include/linux/memcontrol.h
> > +++ b/include/linux/memcontrol.h
> > @@ -679,11 +679,23 @@ static inline unsigned long lruvec_page_state_local(struct lruvec *lruvec,
> >         return x;
> >  }
> >
> > +void __mod_memcg_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx,
> > +                             int val);
> >  void __mod_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx,
> >                         int val);
> >  void __mod_lruvec_slab_state(void *p, enum node_stat_item idx, int val);
> >  void mod_memcg_obj_state(void *p, int idx, int val);
> >
> > +static inline void mod_memcg_lruvec_state(struct lruvec *lruvec,
> > +                                         enum node_stat_item idx, int val)
> 
> Is this function used in later patches? Any benefit introducing it
> here instead of in the patch where it is used for the first time?

Yes, it's used in "mm: memcg/slab: charge individual slab objects instead of pages".

It's a fairly large patchset with many internal dependencies, so there is
always a trade-off between putting everything into a single patch, which is
hard to review, and splitting out some changes, which make not much sense
without seeing the whole picture.

In this particular case splitting out a formal and easy-to-verify change makes
the actual non-trivial patch smaller and hopefully easier for a review.

But of course it's all subjective.

Thanks!