From: Miaohe Lin <linmiaohe@huawei.com>
To: Mike Kravetz <mike.kravetz@oracle.com>
Cc: "Muchun Song" <songmuchun@bytedance.com>,
"Naoya Horiguchi" <nao.horiguchi@gmail.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"David Hildenbrand" <david@redhat.com>,
"Liu Shixin" <liushixin2@huawei.com>,
"Yang Shi" <shy828301@gmail.com>,
"Oscar Salvador" <osalvador@suse.de>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
"HORIGUCHI NAOYA(堀口 直也)" <naoya.horiguchi@nec.com>
Subject: Re: [PATCH v2 1/9] mm/hugetlb: remove checking hstate_is_gigantic() in return_unused_surplus_pages()
Date: Tue, 28 Jun 2022 11:01:11 +0800 [thread overview]
Message-ID: <227ccd06-a945-e4c5-8cff-37817f777781@huawei.com> (raw)
In-Reply-To: <Yrnn+QS8JCMT/3JV@monkey>
On 2022/6/28 1:25, Mike Kravetz wrote:
> On 06/27/22 06:02, HORIGUCHI NAOYA(堀口 直也) wrote:
>> On Fri, Jun 24, 2022 at 12:11:07PM -0700, Mike Kravetz wrote:
>>> On 06/24/22 08:34, HORIGUCHI NAOYA(堀口 直也) wrote:
>>>> On Fri, Jun 24, 2022 at 04:15:19PM +0800, Miaohe Lin wrote:
>>>>> On 2022/6/24 16:03, Muchun Song wrote:
>>>>>> On Fri, Jun 24, 2022 at 10:25:48AM +0800, Miaohe Lin wrote:
>>>>>>> On 2022/6/24 7:51, Naoya Horiguchi wrote:
>>>>>>>> From: Naoya Horiguchi <naoya.horiguchi@nec.com>
>>>>>>>
>>>>>>> IIUC it might be better to do the below check:
>>>>>>> /*
>>>>>>> * Cannot return gigantic pages currently if runtime gigantic page
>>>>>>> * allocation is not supported.
>>>>>>> */
>>>>>>> if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
>>>>>>> goto out;
>>>>>>>
>>>>>>
>>>>>> The change looks good to me. However, the comments above is unnecessary
>>>>>> since gigantic_page_runtime_supported() is straightforward.
>>>>>
>>>>> Agree. The comments can be removed.
>>>>
>>>> Thank you, both. Adding !gigantic_page_runtime_supported without comment
>>>> makes sense to me.
>>>
>>> The change above makes sense to me. However, ...
>>>
>>> If we make the change above, will we have the same strange situation described
>>> in the commit message when !gigantic_page_runtime_supported() is true?
>>>
>>> IIUC, !gigantic_page_runtime_supported implies that gigantic hugetlb
>>> pages can not be allocated or freed at run time. They can only be
>>> allocated at boot time. So, there should NEVER be surplus gigantic
>>> pages if !gigantic_page_runtime_supported().
>>
>> I have the same understanding as the above.
>>
>>> To avoid this situation,
>>> perhaps we should change set_max_huge_pages as follows (not tested)?
>>
>> The suggested diff looks clearer about what it does, so I'd like to take it
>> in the next version. Then, what do we do on the "if (hstate_if_gigantic())"
>> check in return_unused_surplus_pages in the original suggestion? Should it
>> be kept as is, or removed, or checked with !gigantic_page_runtime_supported()?
>> I guess that the new checks prevent calling return_unused_surplus_pages()
>> during pool shrinking, so the check seems not necessary any more.
>
> My first thought was to keep the check in return_unused_surplus_pages() as it
> is called in other code paths. However, it SHOULD only try to free surplus
> hugetlb pages. With the modifications to set_max_huge_pages we will not
> have any surplus gigantic pages if !gigantic_page_runtime_supported, so
> the check can be removed.
>
> Also note that we never try to dynamically allocate surplus gigantic pages.
> This also is left over from the time when we could not easily allocate a
> gigantic page at runtime. It would not surprise me if someone found a use
> case to ease this restriction in the future. Especially so if 1G THP support
> is ever added. If this happens, the check would be necessary and I would
> guess that it would not be added.
>
> Sorry for thinking our loud!!! Although not necessary, it 'might' be a good
> idea to leave the check because it would be overlooked if dynamic allocation
> of gigantic surplus pages is ever added. I do not have a strong opinion.
>
> P.S. This also reminds me that a similar check should be added to the
> demote hugetlb code path. It would be bad if !gigantic_page_runtime_supported
> and we demoted a gigantic page into numerous non-gigantic pages. I will
> send a patch.
Out-of-topic
There're some places check "if (hstate_is_gigantic(h))" while others check
"if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())". Should
we make it explicit in some manner when gigantic_page_runtime_supported is
needed to make code easier to follow?
Just a trivial suggestion. Thanks!
>
next prev parent reply other threads:[~2022-06-28 3:01 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-23 23:51 [PATCH v2 0/9] mm, hwpoison: enable 1GB hugepage support (v2) Naoya Horiguchi
2022-06-23 23:51 ` [PATCH v2 1/9] mm/hugetlb: remove checking hstate_is_gigantic() in return_unused_surplus_pages() Naoya Horiguchi
2022-06-24 2:25 ` Miaohe Lin
2022-06-24 8:03 ` Muchun Song
2022-06-24 8:15 ` Miaohe Lin
2022-06-24 8:34 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-24 19:11 ` Mike Kravetz
2022-06-27 6:02 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-27 17:25 ` Mike Kravetz
2022-06-28 3:01 ` Miaohe Lin [this message]
2022-06-28 8:38 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-30 2:27 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-23 23:51 ` [PATCH v2 2/9] mm/hugetlb: separate path for hwpoison entry in copy_hugetlb_page_range() Naoya Horiguchi
2022-06-24 9:23 ` Miaohe Lin
2022-06-27 6:06 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-24 20:57 ` Mike Kravetz
2022-06-27 6:48 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-27 7:57 ` Muchun Song
2022-06-23 23:51 ` [PATCH v2 3/9] mm/hugetlb: make pud_huge() and huge_pud() aware of non-present pud entry Naoya Horiguchi
2022-06-24 8:40 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-25 0:02 ` Mike Kravetz
2022-06-27 7:07 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-25 9:42 ` Miaohe Lin
2022-06-27 7:24 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-23 23:51 ` [PATCH v2 4/9] mm, hwpoison, hugetlb: support saving mechanism of raw error pages Naoya Horiguchi
2022-06-27 3:16 ` Miaohe Lin
2022-06-27 7:56 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-27 9:26 ` Muchun Song
2022-06-28 2:41 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-28 6:26 ` Muchun Song
2022-06-28 7:51 ` Muchun Song
2022-06-28 8:17 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-28 10:37 ` Muchun Song
2022-06-23 23:51 ` [PATCH v2 5/9] mm, hwpoison: make unpoison aware of raw error info in hwpoisoned hugepage Naoya Horiguchi
2022-06-27 8:32 ` Miaohe Lin
2022-06-27 11:48 ` Miaohe Lin
2022-06-23 23:51 ` [PATCH v2 6/9] mm, hwpoison: set PG_hwpoison for busy hugetlb pages Naoya Horiguchi
2022-06-27 8:39 ` Miaohe Lin
2022-06-23 23:51 ` [PATCH v2 7/9] mm, hwpoison: make __page_handle_poison returns int Naoya Horiguchi
2022-06-27 9:02 ` Miaohe Lin
2022-06-28 6:02 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-23 23:51 ` [PATCH v2 8/9] mm, hwpoison: skip raw hwpoison page in freeing 1GB hugepage Naoya Horiguchi
2022-06-27 12:24 ` Miaohe Lin
2022-06-23 23:51 ` [PATCH v2 9/9] mm, hwpoison: enable memory error handling on " Naoya Horiguchi
2022-06-28 2:06 ` Miaohe Lin
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