Re: [PATCH V4 1/2] mm: add defines for min/max swappiness

[Huan Yang]

在 2023/12/14 0:41, Dan Schatzberg 写道:
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> On Wed, Dec 13, 2023 at 09:58:26AM +0800, Huan Yang wrote:
> > 在 2023/12/13 9:38, Dan Schatzberg 写道:
> > > [????????? schatzberg.dan@xxxxxxxxx ????????? https://aka.ms/LearnAboutSenderIdentification,????????????]
> > >
> > > We use the constants 0 and 200 in a few places in the mm code when
> > > referring to the min and max swappiness. This patch adds MIN_SWAPPINESS
> > > and MAX_SWAPPINESS #defines to improve clarity. There are no functional
> > > changes.
> > >
> > > Signed-off-by: Dan Schatzberg <schatzberg.dan@xxxxxxxxx>
> > > ---
> > >    include/linux/swap.h |  2 ++
> > >    mm/memcontrol.c      |  2 +-
> > >    mm/vmscan.c          | 10 +++++-----
> > >    3 files changed, 8 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/include/linux/swap.h b/include/linux/swap.h
> > > index f6dd6575b905..e2ab76c25b4a 100644
> > > --- a/include/linux/swap.h
> > > +++ b/include/linux/swap.h
> > > @@ -407,6 +407,8 @@ extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
> > >
> > >    #define MEMCG_RECLAIM_MAY_SWAP (1 << 1)
> > >    #define MEMCG_RECLAIM_PROACTIVE (1 << 2)
> > > +#define MIN_SWAPPINESS 0
> > > +#define MAX_SWAPPINESS 200
> > Do MAX_SWAPPINESS apply for all swapppiness? If so, maybe better change
> > swappiness sysctl define:
> > ```
> > sysctl.c:
> >
> > {
> >          .procname    = "swappiness",
> >          .data        = &vm_swappiness,
> >          .maxlen        = sizeof(vm_swappiness),
> >          .mode        = 0644,
> >          .proc_handler    = proc_dointvec_minmax,
> >          .extra1        = SYSCTL_ZERO,
> >          .extra2        = SYSCTL_TWO_HUNDRED,
> >      },
> >
> > ```
> >
> > Here hard code swappiness in [0, 200], and now add a new define.
> Yes, MAX_SWAPPINESS is a hard limit. I'm not sure what you're
> proposing here - the SYSCTL_ZERO and SYSCTL_TWO_HUNDRED values are a
I mean, MAX_SWAPPINESS and SYSCTL_TWO_HUNDRED  all limit swappiness,
but  are different definitions.

If swappiness change 200 into 400, you need to change here extra2 and your
MAX_SWAPPINESS. It's wierd.
> little different than the defines I added. I think most of the value
> is just consistently using the defines in the core mm code.
>
> > And many other code hard reference 200 into max value of swappiness, like:
> >
> > ```
> > memcontrol.c:
> > static int mem_cgroup_swappiness_write(struct cgroup_subsys_state *css,
> >                         struct cftype *cft, u64 val)
> > {
> >      struct mem_cgroup *memcg = mem_cgroup_from_css(css);
> >
> >      if (val > 200)
> >          return -EINVAL;
> >
> >      if (!mem_cgroup_is_root(memcg))
> >          memcg->swappiness = val;
> >      else
> >          vm_swappiness = val;
> >
> >      return 0;
> > }
> This one is already fixed in my patch.