linux-kernel - Re: [PATCH 1/4] hugetlb: skip to end of PT page mapping when pte not present

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Date:   Fri, 17 Jun 2022 17:26:31 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Peter Xu <peterx@...hat.com>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Linux-sh list <linux-sh@...r.kernel.org>,
        sparclinux <sparclinux@...r.kernel.org>,
        "linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@...r.kernel.org>,
        Parisc List <linux-parisc@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Muchun Song <songmuchun@...edance.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Michal Hocko <mhocko@...e.com>,
        Naoya Horiguchi <naoya.horiguchi@...ux.dev>,
        James Houghton <jthoughton@...gle.com>,
        Mina Almasry <almasrymina@...gle.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/4] hugetlb: skip to end of PT page mapping when pte not present

Hi Peter,

On Fri, Jun 17, 2022 at 4:22 PM Peter Xu <peterx@...hat.com> wrote:
> On Thu, Jun 16, 2022 at 02:05:15PM -0700, Mike Kravetz wrote:
> > @@ -6877,6 +6896,39 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
> >       return (pte_t *)pmd;
> >  }
> >
> > +/*
> > + * Return a mask that can be used to update an address to the last huge
> > + * page in a page table page mapping size.  Used to skip non-present
> > + * page table entries when linearly scanning address ranges.  Architectures
> > + * with unique huge page to page table relationships can define their own
> > + * version of this routine.
> > + */
> > +unsigned long hugetlb_mask_last_page(struct hstate *h)
> > +{
> > +     unsigned long hp_size = huge_page_size(h);
> > +
> > +     switch (hp_size) {
> > +     case P4D_SIZE:
> > +             return PGDIR_SIZE - P4D_SIZE;
> > +     case PUD_SIZE:
> > +             return P4D_SIZE - PUD_SIZE;
> > +     case PMD_SIZE:
> > +             return PUD_SIZE - PMD_SIZE;
> > +     default:
>
> Should we add a WARN_ON_ONCE() if it should never trigger?

And with panic_on_warn, it'll panic only once ;-)

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds