linux-kernel - Re: [PATCH] mm: huge_memory: don't start_stop

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Message-ID: <a9ff9028-a73a-4a80-b38a-266d1e8c20fe@redhat.com>
Date: Fri, 26 Jul 2024 11:48:35 +0200
From: David Hildenbrand <david@...hat.com>
To: Ryan Roberts <ryan.roberts@....com>, Barry Song <21cnbao@...il.com>,
 akpm@...ux-foundation.org, linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org, Barry Song <v-songbaohua@...o.com>,
 Lance Yang <ioworker0@...il.com>, Baolin Wang
 <baolin.wang@...ux.alibaba.com>, Yang Shi <shy828301@...il.com>,
 Zi Yan <ziy@...dia.com>
Subject: Re: [PATCH] mm: huge_memory: don't start_stop_khugepaged for non-PMD
 THP

On 26.07.24 11:43, Ryan Roberts wrote:
> On 26/07/2024 09:28, Barry Song wrote:
>> From: Barry Song <v-songbaohua@...o.com>
>>
>> khugepaged will be automatically started when PMD-sized THP is enabled
>> (either of the per-size anon control or the top-level control are set
>> to "always" or "madvise"), and it'll be automatically shutdown when
>> PMD-sized THP is disabled (when both the per-size anon control and the
>> top-level control are "never").
>>
>> It seems unnecessary to call start_stop_khugepaged() for non-PMD THP,
>> as it would only waste CPU time.
>>
>> Cc: Lance Yang <ioworker0@...il.com>
>> Cc: Ryan Roberts <ryan.roberts@....com>
>> Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>
>> Cc: David Hildenbrand <david@...hat.com>
>> Cc: Yang Shi <shy828301@...il.com>
>> Cc: Zi Yan <ziy@...dia.com>
>> Signed-off-by: Barry Song <v-songbaohua@...o.com>
>> ---
>>   mm/huge_memory.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index 41460847988c..bd365e35acf7 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -514,7 +514,7 @@ static ssize_t thpsize_enabled_store(struct kobject *kobj,
>>   	} else
>>   		ret = -EINVAL;
>>   
>> -	if (ret > 0) {
>> +	if (ret > 0 && order == HPAGE_PMD_ORDER) {
>>   		int err;
>>   
>>   		err = start_stop_khugepaged();
> 
> Personally I see this as a bit of a layering violation; its
> start_stop_khugepaged() that should decide the policy for when to start and stop
> the daemon. thpsize_enabled_store() should just be calling
> start_stop_khugepaged() to notify that something potentially pertinent to the a
> policy decision has changed.

Agreed, skimming the subject I was under the impression that we would be 
fixing something here.

-- 
Cheers,

David / dhildenb