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From:   Muchun Song <songmuchun@bytedance.com>
Date:   Thu, 29 Apr 2021 12:02:46 +0800
Message-ID: <CAMZfGtUqE6OzWwK6o5h0j6qHPotfvbKpGbzYpSPLLhYH2nJiAw@mail.gmail.com>
Subject: Re: [External] Re: [PATCH v21 0/9] Free some vmemmap pages of HugeTLB page
To:     Mike Kravetz <mike.kravetz@oracle.com>
Cc:     Jonathan Corbet <corbet@lwn.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, bp@alien8.de,
        X86 ML <x86@kernel.org>, hpa@zytor.com,
        dave.hansen@linux.intel.com, luto@kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>, paulmck@kernel.org,
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        anshuman.khandual@arm.com, jroedel@suse.de,
        Mina Almasry <almasrymina@google.com>,
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        Matthew Wilcox <willy@infradead.org>,
        Oscar Salvador <osalvador@suse.de>,
        Michal Hocko <mhocko@suse.com>,
        "Song Bao Hua (Barry Song)" <song.bao.hua@hisilicon.com>,
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On Thu, Apr 29, 2021 at 10:32 AM Mike Kravetz <mike.kravetz@oracle.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@oracle.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.

>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 9c617c19fc18..f8e5013a6b46 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2420,14 +2420,15 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
>
>         /*
>          * Before dissolving the page, we need to allocate a new one for the
> -        * pool to remain stable. Using alloc_buddy_huge_page() allows us to
> -        * not having to deal with prep_new_huge_page() and avoids dealing of any
> -        * counters. This simplifies and let us do the whole thing under the
> -        * lock.
> +        * pool to remain stable.  Here, we allocate the page and 'prep' it
> +        * by doing everything but actually updating counters and adding to
> +        * the pool.  This simplifies and let us do most of the processing
> +        * under the lock.
>          */
>         new_page = alloc_buddy_huge_page(h, gfp_mask, nid, NULL, NULL);
>         if (!new_page)
>                 return -ENOMEM;
> +       __prep_new_huge_page(h, new_page);
>
>  retry:
>         spin_lock_irq(&hugetlb_lock);
> @@ -2473,7 +2474,6 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
>                  * Reference count trick is needed because allocator gives us
>                  * referenced page but the pool requires pages with 0 refcount.
>                  */
> -               __prep_new_huge_page(h, new_page);
>                 __prep_account_new_huge_page(h, nid);
>                 page_ref_dec(new_page);
>                 enqueue_huge_page(h, new_page);
> @@ -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);
>
>         return ret;
>  }
>
> --
> Mike Kravetz