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

[David Hildenbrand <david@redhat.com>]

On 20.06.20 03:49, Dan Williams wrote:
> On Fri, Jun 19, 2020 at 5:59 AM David Hildenbrand <david@redhat.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@linux-foundation.org>
>> Cc: Johannes Weiner <hannes@cmpxchg.org>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Cc: Minchan Kim <minchan@kernel.org>
>> Cc: Huang Ying <ying.huang@intel.com>
>> Cc: Wei Yang <richard.weiyang@gmail.com>
>> Cc: Mel Gorman <mgorman@techsingularity.net>
>> Cc: Dan Williams <dan.j.williams@intel.com>
>> Signed-off-by: David Hildenbrand <david@redhat.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?

Thanks!

-- 
Thanks,

David / dhildenb