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From:   Liang Li <liliang324@gmail.com>
Date:   Wed, 23 Dec 2020 11:42:12 +0800
Message-ID: <CA+2MQi_ajOZge-_1S0pAt+o-beT6QQru9ogYBcwzAs+tWqrPcQ@mail.gmail.com>
Subject: Re: [RFC PATCH 1/3] mm: support hugetlb free page reporting
To:     Mike Kravetz <mike.kravetz@oracle.com>
Cc:     Alexander Duyck <alexander.duyck@gmail.com>,
        Alexander Duyck <alexander.h.duyck@linux.intel.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Dan Williams <dan.j.williams@intel.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        David Hildenbrand <david@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Michal Hocko <mhocko@suse.com>,
        Liang Li <liliangleo@didiglobal.com>,
        linux-mm <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        virtualization@lists.linux-foundation.org, qemu-devel@nongnu.org
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> On 12/22/20 11:59 AM, Alexander Duyck wrote:
> > On Mon, Dec 21, 2020 at 11:47 PM Liang Li <liliang.opensource@gmail.com> wrote:
> >> +
> >> +       if (huge_page_order(h) > MAX_ORDER)
> >> +               budget = HUGEPAGE_REPORTING_CAPACITY;
> >> +       else
> >> +               budget = HUGEPAGE_REPORTING_CAPACITY * 32;
> >
> > Wouldn't huge_page_order always be more than MAX_ORDER? Seems like we
> > don't even really need budget since this should probably be pulling
> > out no more than one hugepage at a time.
>
> On standard x86_64 configs, 2MB huge pages are of order 9 < MAX_ORDER (11).
> What is important for hugetlb is the largest order that can be allocated
> from buddy.  Anything bigger is considered a gigantic page and has to be
> allocated differently.
>
> If the code above is trying to distinguish between huge and gigantic pages,
> it is off by 1.  The largest order that can be allocated from the buddy is
> (MAX_ORDER - 1).  So, the check should be '>='.
>
> --
> Mike Kravetz

Yes, you're right!  thanks

Liang