From: Mike Kravetz <mike.kravetz@oracle.com>
To: Peter Xu <peterx@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>,
linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org,
catalin.marinas@arm.com, Muchun Song <songmuchun@bytedance.com>,
linux-mips@vger.kernel.org, linux-mm@kvack.org,
James Houghton <jthoughton@google.com>,
sparclinux@vger.kernel.org, will@kernel.org,
Mina Almasry <almasrymina@google.com>,
linux-s390@vger.kernel.org,
Christian Borntraeger <borntraeger@linux.ibm.com>,
Anshuman Khandual <anshuman.khandual@arm.com>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
Paul Walmsley <paul.walmsley@sifive.com>,
Naoya Horiguchi <naoya.horiguchi@linux.dev>,
linux-arm-kernel@lists.infradead.org,
linux-parisc@vger.kernel.org, linux-kernel@vger.kernel.org,
"Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 1/4] hugetlb: skip to end of PT page mapping when pte not present
Date: Fri, 17 Jun 2022 10:17:33 -0700 [thread overview]
Message-ID: <Yqy3LZUOdH5GsZ9j@monkey> (raw)
In-Reply-To: <YqyMhmAjrQ4C+EyA@xz-m1.local>
On 06/17/22 10:15, Peter Xu wrote:
> Hi, Mike,
>
> 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?
>
Sure. I will add this.
> > + break; /* Should never happen */
> > + }
> > +
> > + return ~(0UL);
> > +}
> > +
> > +#else
> > +
> > +/* See description above. Architectures can provide their own version. */
> > +__weak unsigned long hugetlb_mask_last_page(struct hstate *h)
> > +{
> > + return ~(0UL);
>
> I'm wondering whether it's better to return 0 rather than ~0 by default.
> Could an arch with !CONFIG_ARCH_WANT_GENERAL_HUGETLB wrongly skip some
> valid address ranges with ~0, or perhaps I misread?
Thank you, thank you, thank you Peter!
Yes, the 'default' return for hugetlb_mask_last_page() should be 0. If
there is no 'optimization', we do not want to modify the address so we
want to OR with 0 not ~0. My bad, I must have been thinking AND instead
of OR.
I will change here as well as in Baolin's patch.
--
Mike Kravetz
next prev parent reply other threads:[~2022-06-17 17:19 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-16 21:05 [PATCH 0/4] hugetlb: speed up linear address scanning Mike Kravetz
2022-06-16 21:05 ` [PATCH 1/4] hugetlb: skip to end of PT page mapping when pte not present Mike Kravetz
2022-06-17 8:13 ` Muchun Song
2022-06-17 11:26 ` kernel test robot
2022-06-17 21:09 ` Mike Kravetz
2022-06-17 14:15 ` Peter Xu
2022-06-17 15:26 ` Geert Uytterhoeven
2022-06-17 17:17 ` Mike Kravetz [this message]
2022-06-18 3:27 ` Baolin Wang
2022-06-17 17:06 ` kernel test robot
2022-06-16 21:05 ` [PATCH 2/4] arm64/hugetlb: Implement arm64 specific hugetlb_mask_last_page Mike Kravetz
2022-06-17 8:26 ` Muchun Song
2022-06-16 21:05 ` [PATCH 3/4] hugetlb: do not update address in huge_pmd_unshare Mike Kravetz
2022-06-16 21:05 ` [PATCH 4/4] hugetlb: Lazy page table copies in fork() Mike Kravetz
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