linux-kernel - Re: [External] Re: [PATCH v21 0/9] Free some vmemmap pages of HugeTLB page

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Message-ID: <5f363b58-f70a-4a6a-9761-aae93cb49138@oracle.com>
Date:   Thu, 29 Apr 2021 16:19:40 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, bp@...en8.de,
        X86 ML <x86@...nel.org>, hpa@...or.com,
        dave.hansen@...ux.intel.com, luto@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>, paulmck@...nel.org,
        pawan.kumar.gupta@...ux.intel.com,
        Randy Dunlap <rdunlap@...radead.org>, oneukum@...e.com,
        anshuman.khandual@....com, jroedel@...e.de,
        Mina Almasry <almasrymina@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>,
        David Hildenbrand <david@...hat.com>,
        HORIGUCHI NAOYA(堀口 直也) 
        <naoya.horiguchi@....com>,
        Joao Martins <joao.m.martins@...cle.com>,
        Xiongchun duan <duanxiongchun@...edance.com>,
        fam.zheng@...edance.com, zhengqi.arch@...edance.com,
        linux-doc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [External] Re: [PATCH v21 0/9] Free some vmemmap pages of HugeTLB
 page

On 4/29/21 3:23 PM, Mike Kravetz wrote:
> On 4/28/21 9:02 PM, Muchun Song wrote:
>> On Thu, Apr 29, 2021 at 10:32 AM Mike Kravetz <mike.kravetz@...cle.com> wrote:
>>>
>>> On 4/28/21 5:26 AM, Muchun Song wrote:
>>>> On Wed, Apr 28, 2021 at 7:47 AM Mike Kravetz <mike.kravetz@...cle.com> wrote:
>>>>>
>>>>> Thanks!  I will take a look at the modifications soon.
>>>>>
>>>>> I applied the patches to Andrew's mmotm-2021-04-21-23-03, ran some tests and
>>>>> got the following warning.  We may need to special case that call to
>>>>> __prep_new_huge_page/free_huge_page_vmemmap from alloc_and_dissolve_huge_page
>>>>> as it is holding hugetlb lock with IRQs disabled.
>>>>
>>>> Good catch. Thanks Mike. I will fix it in the next version. How about this:
>>>>
>>>> @@ -1618,7 +1617,8 @@ static void __prep_new_huge_page(struct hstate
>>>> *h, struct page *page)
>>>>
>>>>  static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
>>>>  {
>>>> +       free_huge_page_vmemmap(h, page);
>>>>         __prep_new_huge_page(page);
>>>>         spin_lock_irq(&hugetlb_lock);
>>>>         __prep_account_new_huge_page(h, nid);
>>>>         spin_unlock_irq(&hugetlb_lock);
>>>> @@ -2429,6 +2429,7 @@ static int alloc_and_dissolve_huge_page(struct
>>>> hstate *h, struct page *old_page,
>>>>         if (!new_page)
>>>>                 return -ENOMEM;
>>>>
>>>> +       free_huge_page_vmemmap(h, new_page);
>>>>  retry:
>>>>         spin_lock_irq(&hugetlb_lock);
>>>>         if (!PageHuge(old_page)) {
>>>> @@ -2489,7 +2490,7 @@ static int alloc_and_dissolve_huge_page(struct
>>>> hstate *h, struct page *old_page,
>>>>
>>>>  free_new:
>>>>         spin_unlock_irq(&hugetlb_lock);
>>>> -       __free_pages(new_page, huge_page_order(h));
>>>> +       update_and_free_page(h, new_page, false);
>>>>
>>>>         return ret;
>>>>  }
>>>>
>>>>
>>>
>>> Another option would be to leave the prep* routines as is and only
>>> modify alloc_and_dissolve_huge_page as follows:
>>
>> OK. LGTM. I will use this. Thanks Mike.
> 
> There are issues with my suggested patch below.  I am occasionally
> hitting the BUG that checks for page ref count being zero at put_page
> time.  Still do not fully understand, but I do not hit the same BUG
> with your patch above.  Please do not use my patch below.
> 

Ah!  The issue is pretty obvious.


> @@ -2489,7 +2489,7 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
>  
>  free_new:
>  	spin_unlock_irq(&hugetlb_lock);
> -	__free_pages(new_page, huge_page_order(h));
> +	update_and_free_page(h, old_page, false);

That should of course be:
	update_and_free_page(h, new_page, false);

>  
>  	return ret;
>  }
> 

-- 
Mike Kravetz