linux-kernel - Re: [PATCH v2 3/3] mm/shuffle: remove dynamic reconfiguration

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Date:   Tue, 23 Jun 2020 15:18:09 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...e.com>,
        Minchan Kim <minchan@...nel.org>,
        Huang Ying <ying.huang@...el.com>,
        Wei Yang <richard.weiyang@...il.com>,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: Re: [PATCH v2 3/3] mm/shuffle: remove dynamic reconfiguration

On Mon, Jun 22, 2020 at 12:33 AM David Hildenbrand <david@...hat.com> wrote:
>
> On 20.06.20 03:49, Dan Williams wrote:
> > On Fri, Jun 19, 2020 at 5:59 AM David Hildenbrand <david@...hat.com> wrote:
> >>
> >> Commit e900a918b098 ("mm: shuffle initial free memory to improve
> >> memory-side-cache utilization") promised "autodetection of a
> >> memory-side-cache (to be added in a follow-on patch)" over a year ago.
> >>
> >> The original series included patches [1], however, they were dropped
> >> during review [2] to be followed-up later.
> >>
> >> Due to lack of platforms that publish an HMAT, autodetection is currently
> >> not implemented. However, manual activation is actively used [3]. Let's
> >> simplify for now and re-add when really (ever?) needed.
> >>
> >> [1] https://lkml.kernel.org/r/154510700291.1941238.817190985966612531.stgit@dwillia2-desk3.amr.corp.intel.com
> >> [2] https://lkml.kernel.org/r/154690326478.676627.103843791978176914.stgit@dwillia2-desk3.amr.corp.intel.com
> >> [3] https://lkml.kernel.org/r/CAPcyv4irwGUU2x+c6b4L=KbB1dnasNKaaZd6oSpYjL9kfsnROQ@mail.gmail.com
> >>
> >> Cc: Andrew Morton <akpm@...ux-foundation.org>
> >> Cc: Johannes Weiner <hannes@...xchg.org>
> >> Cc: Michal Hocko <mhocko@...e.com>
> >> Cc: Minchan Kim <minchan@...nel.org>
> >> Cc: Huang Ying <ying.huang@...el.com>
> >> Cc: Wei Yang <richard.weiyang@...il.com>
> >> Cc: Mel Gorman <mgorman@...hsingularity.net>
> >> Cc: Dan Williams <dan.j.williams@...el.com>
> >> Signed-off-by: David Hildenbrand <david@...hat.com>
> >> ---
> >>  mm/shuffle.c | 28 ++--------------------------
> >>  mm/shuffle.h | 17 -----------------
> >>  2 files changed, 2 insertions(+), 43 deletions(-)
> >>
> >> diff --git a/mm/shuffle.c b/mm/shuffle.c
> >> index dd13ab851b3ee..9b5cd4b004b0f 100644
> >> --- a/mm/shuffle.c
> >> +++ b/mm/shuffle.c
> >> @@ -10,33 +10,11 @@
> >>  #include "shuffle.h"
> >>
> >>  DEFINE_STATIC_KEY_FALSE(page_alloc_shuffle_key);
> >> -static unsigned long shuffle_state __ro_after_init;
> >> -
> >> -/*
> >> - * Depending on the architecture, module parameter parsing may run
> >> - * before, or after the cache detection. SHUFFLE_FORCE_DISABLE prevents,
> >> - * or reverts the enabling of the shuffle implementation. SHUFFLE_ENABLE
> >> - * attempts to turn on the implementation, but aborts if it finds
> >> - * SHUFFLE_FORCE_DISABLE already set.
> >> - */
> >> -__meminit void page_alloc_shuffle(enum mm_shuffle_ctl ctl)
> >> -{
> >> -       if (ctl == SHUFFLE_FORCE_DISABLE)
> >> -               set_bit(SHUFFLE_FORCE_DISABLE, &shuffle_state);
> >> -
> >> -       if (test_bit(SHUFFLE_FORCE_DISABLE, &shuffle_state)) {
> >> -               if (test_and_clear_bit(SHUFFLE_ENABLE, &shuffle_state))
> >> -                       static_branch_disable(&page_alloc_shuffle_key);
> >> -       } else if (ctl == SHUFFLE_ENABLE
> >> -                       && !test_and_set_bit(SHUFFLE_ENABLE, &shuffle_state))
> >> -               static_branch_enable(&page_alloc_shuffle_key);
> >> -}
> >>
> >>  static bool shuffle_param;
> >>  static int shuffle_show(char *buffer, const struct kernel_param *kp)
> >>  {
> >> -       return sprintf(buffer, "%c\n", test_bit(SHUFFLE_ENABLE, &shuffle_state)
> >> -                       ? 'Y' : 'N');
> >> +       return sprintf(buffer, "%c\n", shuffle_param ? 'Y' : 'N');
> >>  }
> >>
> >>  static __meminit int shuffle_store(const char *val,
> >> @@ -47,9 +25,7 @@ static __meminit int shuffle_store(const char *val,
> >>         if (rc < 0)
> >>                 return rc;
> >>         if (shuffle_param)
> >> -               page_alloc_shuffle(SHUFFLE_ENABLE);
> >> -       else
> >> -               page_alloc_shuffle(SHUFFLE_FORCE_DISABLE);
> >> +               static_branch_enable(&page_alloc_shuffle_key);
> >>         return 0;
> >>  }
> >
> > Let's do proper input validation here and require 1 / 'true' to enable
> > shuffling and not also allow 0 to be an 'enable' value.
>
> I don't think that's currently done?
>
> param_set_bool(val, kp) will only default val==NULL to 'true'. Passing 0
> will properly be handled by strtobool(). Or am I missing something?
>

No, I misread the patch and thought the conditional was being removed.

All good now.