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

Wei Yang
2020-06-22T08:37:30Z

On Mon, Jun 22, 2020 at 09:33:28AM +0200, David Hildenbrand wrote:
>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?
>

Agree with this statement.

>Thanks!
>
>--
>Thanks,
>
>David / dhildenb

--
Wei Yang
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