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Wed, 10 Nov 2021 02:54:39 -0800 (PST) Received: from C02DW0BEMD6R.bytedance.net ([139.177.225.251]) by smtp.gmail.com with ESMTPSA id v38sm5865829pgl.38.2021.11.10.02.54.34 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Wed, 10 Nov 2021 02:54:39 -0800 (PST) From: Qi Zheng To: akpm@linux-foundation.org, tglx@linutronix.de, kirill.shutemov@linux.intel.com, mika.penttila@nextfour.com, david@redhat.com, jgg@nvidia.com Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, songmuchun@bytedance.com, zhouchengming@bytedance.com, Qi Zheng Subject: [PATCH v3 00/15] Free user PTE page table pages Date: Wed, 10 Nov 2021 18:54:13 +0800 Message-Id: <20211110105428.32458-1-zhengqi.arch@bytedance.com> X-Mailer: git-send-email 2.24.3 (Apple Git-128) MIME-Version: 1.0 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: DA9DA5098496 X-Stat-Signature: mnpyz33sdryncipqidnbykbdf5egqcbg Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=bytedance-com.20210112.gappssmtp.com header.s=20210112 header.b=U73ccdfu; spf=pass (imf01.hostedemail.com: domain of zhengqi.arch@bytedance.com designates 209.85.216.45 as permitted sender) smtp.mailfrom=zhengqi.arch@bytedance.com; dmarc=pass (policy=none) header.from=bytedance.com X-HE-Tag: 1636541666-320909 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: Hi, This patch series aims to free user PTE page table pages when all PTE entries are empty. The beginning of this story is that some malloc libraries(e.g. jemalloc or tcmalloc) usually allocate the amount of VAs by mmap() and do not unmap those VAs. They will use madvise(MADV_DONTNEED) to free physical memory if they want. But the page tables do not be freed by madvise(), so it can produce many page tables when the process touches an enormous virtual address space. The following figures are a memory usage snapshot of one process which actually happened on our server: VIRT: 55t RES: 590g VmPTE: 110g As we can see, the PTE page tables size is 110g, while the RES is 590g. In theory, the process only need 1.2g PTE page tables to map those physical memory. The reason why PTE page tables occupy a lot of memory is that madvise(MADV_DONTNEED) only empty the PTE and free physical memory but doesn't free the PTE page table pages. So we can free those empty PTE page tables to save memory. In the above cases, we can save memory about 108g(best case). And the larger the difference between the size of VIRT and RES, the more memory we save. In this patch series, we add a pte_refcount field to the struct page of page table to track how many users of PTE page table. Similar to the mechanism of page refcount, the user of PTE page table should hold a refcount to it before accessing. The PTE page table page will be freed when the last refcount is dropped. Testing: The following code snippet can show the effect of optimization: mmap 50G while (1) { for (; i < 1024 * 25; i++) { touch 2M memory madvise MADV_DONTNEED 2M } } As we can see, the memory usage of VmPTE is reduced: before after VIRT 50.0 GB 50.0 GB RES 3.1 MB 3.6 MB VmPTE 102640 kB 248 kB I also have tested the stability by LTP[1] for several weeks. I have not seen any crash so far. The performance of page fault can be affected because of the allocation/freeing of PTE page table pages. The following is the test result by using a micro benchmark[2]: root@~# perf stat -e page-faults --repeat 5 ./multi-fault $threads: threads before (pf/min) after (pf/min) 1 32,085,255 31,880,833 (-0.64%) 8 101,674,967 100,588,311 (-1.17%) 16 113,207,000 112,801,832 (-0.36%) (The "pfn/min" means how many page faults in one minute.) The performance of page fault is ~1% slower than before. And there are no obvious changes in perf hot spots: before: 19.29% [kernel] [k] clear_page_rep 16.12% [kernel] [k] do_user_addr_fault 9.57% [kernel] [k] _raw_spin_unlock_irqrestore 6.16% [kernel] [k] get_page_from_freelist 5.03% [kernel] [k] __handle_mm_fault 3.53% [kernel] [k] __rcu_read_unlock 3.45% [kernel] [k] handle_mm_fault 3.38% [kernel] [k] down_read_trylock 2.74% [kernel] [k] free_unref_page_list 2.17% [kernel] [k] up_read 1.93% [kernel] [k] charge_memcg 1.73% [kernel] [k] try_charge_memcg 1.71% [kernel] [k] __alloc_pages 1.69% [kernel] [k] ___perf_sw_event 1.44% [kernel] [k] get_mem_cgroup_from_mm after: 18.19% [kernel] [k] clear_page_rep 16.28% [kernel] [k] do_user_addr_fault 8.39% [kernel] [k] _raw_spin_unlock_irqrestore 5.12% [kernel] [k] get_page_from_freelist 4.81% [kernel] [k] __handle_mm_fault 4.68% [kernel] [k] down_read_trylock 3.80% [kernel] [k] handle_mm_fault 3.59% [kernel] [k] get_mem_cgroup_from_mm 2.49% [kernel] [k] free_unref_page_list 2.41% [kernel] [k] up_read 2.16% [kernel] [k] charge_memcg 1.92% [kernel] [k] __rcu_read_unlock 1.88% [kernel] [k] ___perf_sw_event 1.70% [kernel] [k] pte_get_unless_zero This series is based on next-20211108. Comments and suggestions are welcome. Thanks, Qi. [1] https://github.com/linux-test-project/ltp [2] https://lore.kernel.org/lkml/20100106160614.ff756f82.kamezawa.hiroyu@jp.fujitsu.com/2-multi-fault-all.c Changelog in v2 -> v3: - Refactored this patch series: - [PATCH v3 6/15]: Introduce the new dummy helpers first - [PATCH v3 7-12/15]: Convert each subsystem individually - [PATCH v3 13/15]: Implement the actual logic to the dummy helpers And thanks for the advice from David and Jason. - Add a document. Changelog in v1 -> v2: - Change pte_install() to pmd_install(). - Fix some typo and code style problems. - Split [PATCH v1 5/7] into [PATCH v2 4/9], [PATCH v2 5/9]，[PATCH v2 6/9] and [PATCH v2 7/9]. Qi Zheng (15): mm: do code cleanups to filemap_map_pmd() mm: introduce is_huge_pmd() helper mm: move pte_offset_map_lock() to pgtable.h mm: rework the parameter of lock_page_or_retry() mm: add pmd_installed_type return for __pte_alloc() and other friends mm: introduce refcount for user PTE page table page mm/pte_ref: add support for user PTE page table page allocation mm/pte_ref: initialize the refcount of the withdrawn PTE page table page mm/pte_ref: add support for the map/unmap of user PTE page table page mm/pte_ref: add support for page fault path mm/pte_ref: take a refcount before accessing the PTE page table page mm/pte_ref: update the pmd entry in move_normal_pmd() mm/pte_ref: free user PTE page table pages Documentation: add document for pte_ref mm/pte_ref: use mmu_gather to free PTE page table pages Documentation/vm/pte_ref.rst | 216 ++++++++++++++++++++++++++++++++++++ arch/x86/Kconfig | 2 +- fs/proc/task_mmu.c | 24 +++- fs/userfaultfd.c | 9 +- include/linux/huge_mm.h | 10 +- include/linux/mm.h | 170 ++++------------------------- include/linux/mm_types.h | 6 +- include/linux/pagemap.h | 8 +- include/linux/pgtable.h | 152 +++++++++++++++++++++++++- include/linux/pte_ref.h | 146 +++++++++++++++++++++++++ include/linux/rmap.h | 2 + kernel/events/uprobes.c | 2 + mm/Kconfig | 4 + mm/Makefile | 4 +- mm/damon/vaddr.c | 12 +- mm/debug_vm_pgtable.c | 5 +- mm/filemap.c | 45 +++++--- mm/gup.c | 25 ++++- mm/hmm.c | 5 +- mm/huge_memory.c | 3 +- mm/internal.h | 4 +- mm/khugepaged.c | 21 +++- mm/ksm.c | 6 +- mm/madvise.c | 21 +++- mm/memcontrol.c | 12 +- mm/memory-failure.c | 11 +- mm/memory.c | 254 ++++++++++++++++++++++++++++++++----------- mm/mempolicy.c | 6 +- mm/migrate.c | 54 ++++----- mm/mincore.c | 7 +- mm/mlock.c | 1 + mm/mmu_gather.c | 40 +++---- mm/mprotect.c | 11 +- mm/mremap.c | 14 ++- mm/page_vma_mapped.c | 4 + mm/pagewalk.c | 15 ++- mm/pgtable-generic.c | 1 + mm/pte_ref.c | 141 ++++++++++++++++++++++++ mm/rmap.c | 10 ++ mm/swapfile.c | 3 + mm/userfaultfd.c | 40 +++++-- 41 files changed, 1186 insertions(+), 340 deletions(-) create mode 100644 Documentation/vm/pte_ref.rst create mode 100644 include/linux/pte_ref.h create mode 100644 mm/pte_ref.c