linux-kernel - Re: [PATCH v4 3/5] mm: Speedup mremap on 1GB or larger regions

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Message-ID: <20201217172847.GA89104@roeck-us.net>
Date:   Thu, 17 Dec 2020 09:28:47 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Kalesh Singh <kaleshsingh@...gle.com>
Cc:     surenb@...gle.com, minchan@...gle.com, joelaf@...gle.com,
        lokeshgidra@...gle.com, kernel-team@...roid.com,
        kernel test robot <lkp@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Shuah Khan <shuah@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Kees Cook <keescook@...omium.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Hassan Naveed <hnaveed@...ecomp.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Gavin Shan <gshan@...hat.com>, Mike Rapoport <rppt@...nel.org>,
        Steven Price <steven.price@....com>,
        Jia He <justin.he@....com>, John Hubbard <jhubbard@...dia.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Ram Pai <linuxram@...ibm.com>,
        Sandipan Das <sandipan@...ux.ibm.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Brian Geffon <bgeffon@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Ira Weiny <ira.weiny@...el.com>,
        SeongJae Park <sjpark@...zon.de>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v4 3/5] mm: Speedup mremap on 1GB or larger regions

On Wed, Oct 14, 2020 at 12:53:08AM +0000, Kalesh Singh wrote:
> Android needs to move large memory regions for garbage collection.
> The GC requires moving physical pages of multi-gigabyte heap
> using mremap. During this move, the application threads have to
> be paused for correctness. It is critical to keep this pause as
> short as possible to avoid jitters during user interaction.
> 
> Optimize mremap for >= 1GB-sized regions by moving at the PUD/PGD
> level if the source and destination addresses are PUD-aligned.
> For CONFIG_PGTABLE_LEVELS == 3, moving at the PUD level in effect moves
> PGD entries, since the PUD entry is “folded back” onto the PGD entry.
> Add HAVE_MOVE_PUD so that architectures where moving at the PUD level
> isn't supported/tested can turn this off by not selecting the config.
> 
> Fix build test error from v1 of this series reported by
> kernel test robot in [1].
> 
> [1] https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org/thread/CKPGL4FH4NG7TGH2CVYX2UX76L25BTA3/
> 
> Signed-off-by: Kalesh Singh <kaleshsingh@...gle.com>
> Reported-by: kernel test robot <lkp@...el.com>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>

I thought I reported it, but maybe I didn't. This patch causes all
'parisc' qemu emulations to fail. Typical log:

Freeing unused kernel memory: 604K
Write protected read-only-after-init data: 2k
rodata_test: end of .rodata is not page size aligned
Run /sbin/init as init process
process '/bin/busybox' started with executable stack
Failed to execute /sbin/init (error -12)

Reverting this patch fixes the problem.

Bisect log from linux-next below. The patch (and thus the problem)
are now in mainline Linux.

Guenter

---
# bad: [7bba37a1591369e2e506d599b8f5d7d0516b2dbc] Add linux-next specific files for 20201214
# good: [0477e92881850d44910a7e94fc2c46f96faa131f] Linux 5.10-rc7
git bisect start 'HEAD' 'v5.10-rc7'
# good: [fe5c40ab90a1f82ba97294637eaf875cfdd7a05f] Merge remote-tracking branch 'nand/nand/next'
git bisect good fe5c40ab90a1f82ba97294637eaf875cfdd7a05f
# good: [674a0d6de8bd290671f7dff405205871a70300b3] Merge remote-tracking branch 'spi/for-next'
git bisect good 674a0d6de8bd290671f7dff405205871a70300b3
# good: [8623dae312f73a2ea3230b1c648d3004cfc224ce] Merge remote-tracking branch 'vfio/next'
git bisect good 8623dae312f73a2ea3230b1c648d3004cfc224ce
# good: [dd26635f54bcd8e5d4e875a209f82a0423ba9c08] Merge remote-tracking branch 'gpio/for-next'
git bisect good dd26635f54bcd8e5d4e875a209f82a0423ba9c08
# good: [86e9c9a734889fe437442e0a35eb4c61d319cb47] Merge remote-tracking branch 'memblock/for-next'
git bisect good 86e9c9a734889fe437442e0a35eb4c61d319cb47
# bad: [3452331fda80b1cb5e121e6718ca6c07264382b2] userfaultfd: add user-mode only option to unprivileged_userfaultfd sysctl knob
git bisect bad 3452331fda80b1cb5e121e6718ca6c07264382b2
# bad: [19f468d54fcffc3f98b71e3e12ff23726767d953] mremap: don't allow MREMAP_DONTUNMAP on special_mappings and aio
git bisect bad 19f468d54fcffc3f98b71e3e12ff23726767d953
# good: [d89f3ababcac54493a4cb0582c61eb5f426b44e3] mm: remove pagevec_lookup_range_nr_tag()
git bisect good d89f3ababcac54493a4cb0582c61eb5f426b44e3
# good: [eba8373dcb40d30952f31d5fc0cff56b78f46273] mm/mlock: remove __munlock_isolate_lru_page()
git bisect good eba8373dcb40d30952f31d5fc0cff56b78f46273
# good: [8831d3f3564beba0f3f1b5291c88b35725bc45c9] xen/unpopulated-alloc: consolidate pgmap manipulation
git bisect good 8831d3f3564beba0f3f1b5291c88b35725bc45c9
# bad: [b8d53d70851821d8a2040ddca3aa6ee88fc8aaec] mm/page_vma_mapped.c: add colon to fix kernel-doc markups error for check_pte
git bisect bad b8d53d70851821d8a2040ddca3aa6ee88fc8aaec
# bad: [e77846c3da1862faa25c08e186a62b03e98c862f] x86: mremap speedup - Enable HAVE_MOVE_PUD
git bisect bad e77846c3da1862faa25c08e186a62b03e98c862f
# bad: [72ad8951bac1c559ea1b691a0b035fb339e4d71d] mm: speedup mremap on 1GB or larger regions
git bisect bad 72ad8951bac1c559ea1b691a0b035fb339e4d71d
# good: [fa94bfe31609787501a1ff8d7659ade5734ec4e5] kselftests: vm: add mremap tests
git bisect good fa94bfe31609787501a1ff8d7659ade5734ec4e5
# first bad commit: [72ad8951bac1c559ea1b691a0b035fb339e4d71d] mm: speedup mremap on 1GB or larger regions