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 14:09:51 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     kernel test robot <lkp@...el.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-ia64@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        llvm@...ts.linux.dev, kbuild-all@...ts.01.org,
        Muchun Song <songmuchun@...edance.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Michal Hocko <mhocko@...e.com>, Peter Xu <peterx@...hat.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@....com, 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

On 06/17/22 19:26, kernel test robot wrote:
> Hi Mike,
> 
> I love your patch! Yet something to improve:
> 
> [auto build test ERROR on soc/for-next]
> [also build test ERROR on linus/master v5.19-rc2 next-20220617]
> [cannot apply to arm64/for-next/core arm/for-next kvmarm/next xilinx-xlnx/master]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Mike-Kravetz/hugetlb-speed-up-linear-address-scanning/20220617-050726
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/soc/soc.git for-next
> config: i386-randconfig-a002 (https://download.01.org/0day-ci/archive/20220617/202206171929.ZIUrNg6p-lkp@intel.com/config)
> compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project f0e608de27b3d568000046eebf3712ab542979d6)
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # https://github.com/intel-lab-lkp/linux/commit/4c647687607f10fece04967b8180c0dadaf765e6
>         git remote add linux-review https://github.com/intel-lab-lkp/linux
>         git fetch --no-tags linux-review Mike-Kravetz/hugetlb-speed-up-linear-address-scanning/20220617-050726
>         git checkout 4c647687607f10fece04967b8180c0dadaf765e6
>         # save the config file
>         mkdir build_dir && cp config build_dir/.config
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=i386 SHELL=/bin/bash
> 
> If you fix the issue, kindly add following tag where applicable
> Reported-by: kernel test robot <lkp@...el.com>
> 
> All errors (new ones prefixed by >>):

A couple of things here,

> 
> >> mm/hugetlb.c:6901:7: error: duplicate case value '4194304'
>            case PUD_SIZE:
>                 ^
>    include/asm-generic/pgtable-nopud.h:20:20: note: expanded from macro 'PUD_SIZE'
>    #define PUD_SIZE        (1UL << PUD_SHIFT)
>                            ^
>    mm/hugetlb.c:6899:7: note: previous case defined here
>            case P4D_SIZE:
>                 ^
>    include/asm-generic/pgtable-nop4d.h:13:19: note: expanded from macro 'P4D_SIZE'
>    #define P4D_SIZE                (1UL << P4D_SHIFT)

In the CONFIG_ARCH_WANT_GENERAL_HUGETLB case covered by this version of
hugetlb_mask_last_page, huge pages can only be PMD_SIZE or PUD_SIZE.
So, the 'case P4D_SIZE:' should not exist and can be removed.

>                                    ^
>    mm/hugetlb.c:6903:7: error: duplicate case value '4194304'
>            case PMD_SIZE:
>                 ^
>    include/asm-generic/pgtable-nopmd.h:22:20: note: expanded from macro 'PMD_SIZE'
>    #define PMD_SIZE        (1UL << PMD_SHIFT)
>                            ^

On i386 with CONFIG_PGTABLE_LEVELS=2, PUD_SIZE == PMD_SIZE.
Originally, I coded this as a if .. else if ... statement instead of a
switch.  If coded this way, the compiler does not complain about the
duplicate values.  The only other alternative I can think of is
something like '#if CONFIG_PGTABLE_LEVELS > 2' around the PUD_SIZE case.

I would prefer the if else if, unless someone can suggest something else?
-- 
Mike Kravetz