linux-kernel - Re: [PATCH v2 1/4] hugetlb: add demote hugetlb page sysfs interfaces

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Date:   Wed, 29 Sep 2021 11:22:57 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     David Hildenbrand <david@...hat.com>,
        Michal Hocko <mhocko@...e.com>,
        Oscar Salvador <osalvador@...e.de>, Zi Yan <ziy@...dia.com>,
        Muchun Song <songmuchun@...edance.com>,
        Naoya Horiguchi <naoya.horiguchi@...ux.dev>,
        David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 1/4] hugetlb: add demote hugetlb page sysfs interfaces

On 9/24/21 12:08 AM, Aneesh Kumar K.V wrote:
> Mike Kravetz <mike.kravetz@...cle.com> writes:
> 
>> Two new sysfs files are added to demote hugtlb pages.  These files are
>> both per-hugetlb page size and per node.  Files are:
>>   demote_size - The size in Kb that pages are demoted to. (read-write)
>>   demote - The number of huge pages to demote. (write-only)
>>
>> By default, demote_size is the next smallest huge page size.  Valid huge
>> page sizes less than huge page size may be written to this file.  When
>> huge pages are demoted, they are demoted to this size.
>>
>> Writing a value to demote will result in an attempt to demote that
>> number of hugetlb pages to an appropriate number of demote_size pages.
>>
>> NOTE: Demote interfaces are only provided for huge page sizes if there
>> is a smaller target demote huge page size.  For example, on x86 1GB huge
>> pages will have demote interfaces.  2MB huge pages will not have demote
>> interfaces.
> 
> Should we also check if the platform allows for
> gigantic_page_runtime_supported() ? 
> 

Yes, thanks!

Looks like this may only be an issue for giganitc pages on power managed
by firmware.  Still, needs to be checked.  Will update.

Thanks,
-- 
Mike Kravetz