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Tue, 30 Jul 2024 16:08:03 +0000 (GMT) X-AuditID: cbfec7f5-d1bff70000002594-7a-66a90fe33c99 Received: from eusmtip1.samsung.com ( [203.254.199.221]) by eusmgms2.samsung.com (EUCPMTA) with SMTP id 89.68.09010.3EF09A66; Tue, 30 Jul 2024 17:08:03 +0100 (BST) Received: from [106.210.134.192] (unknown [106.210.134.192]) by eusmtip1.samsung.com (KnoxPortal) with ESMTPA id 20240730160802eusmtip1cdffbf7ba0218fe3298cf1c448deaa5b~nCV5EDYwC3203132031eusmtip1x; Tue, 30 Jul 2024 16:08:02 +0000 (GMT) Message-ID: Date: Tue, 30 Jul 2024 18:08:02 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 1/2] mm: let pte_lockptr() consume a pte_t pointer To: David Hildenbrand , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Andrew Morton , Muchun Song , Peter Xu , Oscar Salvador Content-Language: en-US From: Marek Szyprowski In-Reply-To: <82e77547-5116-4ef2-a232-f5ab1fca7e02@redhat.com> Content-Transfer-Encoding: 8bit X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFlrAKsWRmVeSWpSXmKPExsWy7djP87qP+VemGazbbWoxZ/0aNouv638x W1zeNYfN4t6a/6wWy3Y+ZLE4M63IYsv+b+wO7B6bPk1i9zgx4zeLx8KGqcwe7/ddZfPYfLra 4/MmuQC2KC6blNSczLLUIn27BK6M+Yt3MRfcEqp4scGkgXEOfxcjJ4eEgInE9aMnmLoYuTiE BFYwSqzf1s8O4XxhlDjZ0s8K4XwGykyYywjT8uD3CWaIxHJGiRl/LkNVfWSU+NK+CCjDwcEr YCfx6VoESAOLgKrE34ZLYM28AoISJ2c+YQGxRQXkJe7fmsEOYgsLeEp8/NfBBNIqIuAmMWFR JMhIZoE1jBJ3++eD1TALiEvcejKfCcRmEzCU6HrbxQZicwKt2rVnPxtEjbxE89bZYMdJCDzh kFj3fT3U1S4Sm/ufMUHYwhKvjm9hh7BlJP7vnM8E0dDOKLHg930oZwKjRMPzW1Dd1hJ3zv1i AzmPWUBTYv0ufYiwo8T0A41gD0sI8EnceCsIcQSfxKRt06HCvBIdbUIQ1WoSs46vg1t78MIl 5gmMSrOQgmUWkjdnIXlnFsLeBYwsqxjFU0uLc9NTi43zUsv1ihNzi0vz0vWS83M3MQIT0el/ x7/uYFzx6qPeIUYmDsZDjBIczEoivPFXlqYJ8aYkVlalFuXHF5XmpBYfYpTmYFES51VNkU8V EkhPLEnNTk0tSC2CyTJxcEo1MBkbNxws2zfhV0xuZdCRuuaMCbddrNQcWfuPSlxYoZlj9er0 45k7q/duDp0toZ3toHn10eOtl3/X/nYxMGr1+bdcMbuBZz/Diuy7ZapCDZVsYk9/NZiVF02a 8KJ8Znufo/L5nT31HxkvB347dWuTzpyoJ8nsJ/S7jV7s0wryCTNNE51sWTttstHfZav3F/st jhI167/edXvbh4riBdcq8jM26HYlMir8iLyqys+0ppPzF/fdPPXTnq2vLdz+rZfibNh0o7/3 rcAU0f85t97eWmRn8ZexwDTHcdOuXRyqyz44yEbusp/4pfvJ6+6nzlOeq293WXy99QxPqMBL b+V9lzd3y149obP1nEdQxPeb0kosxRmJhlrMRcWJALcp3P+zAwAA X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFtrEIsWRmVeSWpSXmKPExsVy+t/xu7qP+VemGcyfIG8xZ/0aNouv638x W1zeNYfN4t6a/6wWy3Y+ZLE4M63IYsv+b+wO7B6bPk1i9zgx4zeLx8KGqcwe7/ddZfPYfLra 4/MmuQC2KD2bovzSklSFjPziElulaEMLIz1DSws9IxNLPUNj81grI1MlfTublNSczLLUIn27 BL2M+Yt3MRfcEqp4scGkgXEOfxcjJ4eEgInEg98nmLsYuTiEBJYySvxpusUCkZCRODmtgRXC Fpb4c62LDaLoPaNE28fjQEUcHLwCdhKfrkWA1LAIqEr8bbjECGLzCghKnJz5BGyOqIC8xP1b M9hBbGEBT4mP/zqYQFpFBNwkJiyKBBnJLLCGUeJ481eoI64xSXw93Q3WwCwgLnHryXwmEJtN wFCi6y3IEZwcnEB7d+3ZzwZRYybRtbWLEcKWl2jeOpt5AqPQLCR3zEIyahaSlllIWhYwsqxi FEktLc5Nzy020itOzC0uzUvXS87P3cQIjLxtx35u2cG48tVHvUOMTByMhxglOJiVRHjjryxN E+JNSaysSi3Kjy8qzUktPsRoCgyMicxSosn5wNjPK4k3NDMwNTQxszQwtTQzVhLn9SzoSBQS SE8sSc1OTS1ILYLpY+LglGpgWi1nOGfZecu0c/unfHu2fM6/z8F1qzQutrr7l05aUqhuES+/ tm2KlspX59snnsXyts+sdNJNZSudfl0iRVDeqltVU7hm/9v3aYuk2R+fzfG+9K9+xY9JwYq9 11ZLyfP1uWaF3pJpk9/0IHBBzJ3+nB+eBsHys/tXtTUvP7Js9yxeWfONRR2an7W8HhgnfRZf lmyhq2U0X+61rlml9bIXORPi+guz37esWdniOok/N/pFcoVoYO6s0My3hl8PRjVt6oiMsQmy 9xO85/SUadb3BM7JVd7vJk9pql/5nDny0PV1OwS2/K+I2b8g4JzugmSlkDCmuo5Fi+foS258 Etc9v4jjH//2m15MCpeUw5OVWIozEg21mIuKEwGKv7TBRQMAAA== X-CMS-MailID: 20240730160803eucas1p18569f012751560f5d4e5d3c17a88dff4 X-Msg-Generator: CA Content-Type: text/plain; charset="utf-8" X-RootMTR: 20240730153058eucas1p2319e4cc985dcdc6e98d08398c33fcfd3 X-EPHeader: CA CMS-TYPE: 201P X-CMS-RootMailID: 20240730153058eucas1p2319e4cc985dcdc6e98d08398c33fcfd3 References: <20240725183955.2268884-1-david@redhat.com> <20240725183955.2268884-2-david@redhat.com> <97d87df8-6076-4df0-90a9-a8f5ddea42e9@samsung.com> <82e77547-5116-4ef2-a232-f5ab1fca7e02@redhat.com> X-Stat-Signature: rho57wmxfk4nznne6ig3zuayh3h7ciuq X-Rspamd-Queue-Id: B7B34A0020 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1722355686-441612 X-HE-Meta: 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 9YMGwo7n f84X+hl/ARgopnNMtIpQTtvwwiYXIu32q+rW3PdOsf33X6Go2wUPN9wMns7B2HfJ7Lgmc6ei/3KJIdF/N7en5EcgiuPBMm9GvEiqez2tXwImAlVqDlvFbWtc/T3R5GgXZTO+Or1jrxvduQCpoFCB8snzEjEkDVt9HHI97mxbidYpfjxhF2pULFOwlaw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 30.07.2024 17:49, David Hildenbrand wrote: > On 30.07.24 17:45, David Hildenbrand wrote: >> On 30.07.24 17:30, Marek Szyprowski wrote: >>> On 25.07.2024 20:39, David Hildenbrand wrote: >>>> pte_lockptr() is the only *_lockptr() function that doesn't consume >>>> what would be expected: it consumes a pmd_t pointer instead of a pte_t >>>> pointer. >>>> >>>> Let's change that. The two callers in pgtable-generic.c are easily >>>> adjusted. Adjust khugepaged.c:retract_page_tables() to simply do a >>>> pte_offset_map_nolock() to obtain the lock, even though we won't >>>> actually >>>> be traversing the page table. >>>> >>>> This makes the code more similar to the other variants and avoids >>>> other >>>> hacks to make the new pte_lockptr() version happy. pte_lockptr() users >>>> reside now only in  pgtable-generic.c. >>>> >>>> Maybe, using pte_offset_map_nolock() is the right thing to do because >>>> the PTE table could have been removed in the meantime? At least it >>>> sounds >>>> more future proof if we ever have other means of page table reclaim. >>>> >>>> It's not quite clear if holding the PTE table lock is really required: >>>> what if someone else obtains the lock just after we unlock it? But >>>> we'll >>>> leave that as is for now, maybe there are good reasons. >>>> >>>> This is a preparation for adapting hugetlb page table locking logic to >>>> take the same locks as core-mm page table walkers would. >>>> >>>> Signed-off-by: David Hildenbrand >>> >>> This patch landed in today's linux-next as commit e98970a1d2d4 ("mm: >>> let >>> pte_lockptr() consume a pte_t pointer"). Unfortunately it causes the >>> following issue on most of my ARM 32bit based test boards: >>> >> >> That is ... rather surprising. >> >> The issue below seems to point at __pte_offset_map_lock(), where we >> essentially convert from >> >> ptlock_ptr(page_ptdesc(pmd_page(*pmd))); >> >> to >> >> ptlock_ptr(virt_to_ptdesc(pte)); > > I'm wondering, is highmem involved here such that the PTE would be > kmap'ed and virt_to_page() would not do what we would expect it to do? Yes, highmem is enabled on those boards and all of them have 1GB+ of RAM. For other kernel configuration options see arch/arm/configs/exynos_defconfig. Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland