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Subject: Re: [PATCH v4 3/8] hugetlb: perform vmemmap optimization on a list of
 pages
From:   Muchun Song <muchun.song@linux.dev>
In-Reply-To: <20230919204954.GA425719@monkey>
Date:   Wed, 20 Sep 2023 11:05:30 +0800
Cc:     Linux-MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>,
        Muchun Song <songmuchun@bytedance.com>,
        Joao Martins <joao.m.martins@oracle.com>,
        Oscar Salvador <osalvador@suse.de>,
        David Hildenbrand <david@redhat.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        David Rientjes <rientjes@google.com>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        Naoya Horiguchi <naoya.horiguchi@linux.dev>,
        Barry Song <21cnbao@gmail.com>, Michal Hocko <mhocko@suse.com>,
        Matthew Wilcox <willy@infradead.org>,
        Xiongchun Duan <duanxiongchun@bytedance.com>,
        Andrew Morton <akpm@linux-foundation.org>
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References: <20230918230202.254631-1-mike.kravetz@oracle.com>
 <20230918230202.254631-4-mike.kravetz@oracle.com>
 <e284396d-c32d-b69d-21c6-7025db93b873@linux.dev>
 <20230919204954.GA425719@monkey>
To:     Mike Kravetz <mike.kravetz@oracle.com>
Precedence: bulk


> On Sep 20, 2023, at 04:49, Mike Kravetz <mike.kravetz@oracle.com> =
wrote:
>=20
> On 09/19/23 11:10, Muchun Song wrote:
>>=20
>>=20
>> On 2023/9/19 07:01, Mike Kravetz wrote:
>>> When adding hugetlb pages to the pool, we first create a list of the
>>> allocated pages before adding to the pool.  Pass this list of pages =
to a
>>> new routine hugetlb_vmemmap_optimize_folios() for vmemmap =
optimization.
>>>=20
>>> Due to significant differences in vmemmmap initialization for =
bootmem
>>> allocated hugetlb pages, a new routine prep_and_add_bootmem_folios
>>> is created.
>>>=20
>>> We also modify the routine vmemmap_should_optimize() to check for =
pages
>>> that are already optimized.  There are code paths that might request
>>> vmemmap optimization twice and we want to make sure this is not
>>> attempted.
>>>=20
>>> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
>>> ---
>>>  mm/hugetlb.c         | 50 =
+++++++++++++++++++++++++++++++++++++-------
>>>  mm/hugetlb_vmemmap.c | 11 ++++++++++
>>>  mm/hugetlb_vmemmap.h |  5 +++++
>>>  3 files changed, 58 insertions(+), 8 deletions(-)
>>>=20
>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>>> index 8624286be273..d6f3db3c1313 100644
>>> --- a/mm/hugetlb.c
>>> +++ b/mm/hugetlb.c
>>> @@ -2269,6 +2269,11 @@ static void =
prep_and_add_allocated_folios(struct hstate *h,
>>>  {
>>>   struct folio *folio, *tmp_f;
>>> + /*
>>> +  * Send list for bulk vmemmap optimization processing
>>> +  */
>>=20
>> =46rom the kernel development document, one-line comment format is =
"/**/".
>>=20
>=20
> Will change the comments introduced here.

BTW, there are some places as well, please updates all, thanks.

>=20
>>> + hugetlb_vmemmap_optimize_folios(h, folio_list);
>>> +
>>>   /*
>>>    * Add all new pool pages to free lists in one lock cycle
>>>    */
>>> @@ -3309,6 +3314,40 @@ static void __init =
hugetlb_folio_init_vmemmap(struct folio *folio,
>>>   prep_compound_head((struct page *)folio, huge_page_order(h));
>>>  }
>>> +static void __init prep_and_add_bootmem_folios(struct hstate *h,
>>> + struct list_head *folio_list)
>>> +{
>>> + struct folio *folio, *tmp_f;
>>> +
>>> + /*
>>> +  * Send list for bulk vmemmap optimization processing
>>> +  */
>>> + hugetlb_vmemmap_optimize_folios(h, folio_list);
>>> +
>>> + /*
>>> +  * Add all new pool pages to free lists in one lock cycle
>>> +  */
>>> + spin_lock_irq(&hugetlb_lock);
>>> + list_for_each_entry_safe(folio, tmp_f, folio_list, lru) {
>>> + if (!folio_test_hugetlb_vmemmap_optimized(folio)) {
>>> + /*
>>> +  * If HVO fails, initialize all tail struct pages
>>> +  * We do not worry about potential long lock hold
>>> +  * time as this is early in boot and there should
>>> +  * be no contention.
>>> +  */
>>> + hugetlb_folio_init_tail_vmemmap(folio,
>>> + HUGETLB_VMEMMAP_RESERVE_PAGES,
>>> + pages_per_huge_page(h));
>>> + }
>>> + __prep_account_new_huge_page(h, folio_nid(folio));
>>> + enqueue_hugetlb_folio(h, folio);
>>> + }
>>> + spin_unlock_irq(&hugetlb_lock);
>>> +
>>> + INIT_LIST_HEAD(folio_list);
>>=20
>> I'm not sure what is the purpose of the reinitialization to list =
head?
>>=20
>=20
> There really is no purpose.  This was copied from
> prep_and_add_allocated_folios which also has this unnecessary call.  =
It is
> unnecessary as enqueue_hugetlb_folio() will do a list_move for each
> folio on the list.  Therefore, at the end of the loop we KNOW the list
> is empty.

Right.

>=20
> I will remove here and in prep_and_add_allocated_folios.

Thanks.

>=20
> Thanks,
> --=20
> Mike Kravetz