Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756255AbbBLQS5 (ORCPT ); Thu, 12 Feb 2015 11:18:57 -0500 Received: from mga14.intel.com ([192.55.52.115]:38986 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755708AbbBLQSy (ORCPT ); Thu, 12 Feb 2015 11:18:54 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.09,565,1418112000"; d="scan'208";a="665481011" From: "Kirill A. Shutemov" To: Andrew Morton , Andrea Arcangeli , Hugh Dickins Cc: Dave Hansen , Mel Gorman , Rik van Riel , Vlastimil Babka , Christoph Lameter , Naoya Horiguchi , Steve Capper , "Aneesh Kumar K.V" , Johannes Weiner , Michal Hocko , Jerome Marchand , linux-kernel@vger.kernel.org, linux-mm@kvack.org, "Kirill A. Shutemov" Subject: [PATCHv3 00/24] THP refcounting redesign Date: Thu, 12 Feb 2015 18:18:14 +0200 Message-Id: <1423757918-197669-1-git-send-email-kirill.shutemov@linux.intel.com> X-Mailer: git-send-email 2.1.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9978 Lines: 253 Hello everybody, Here's the first non-RFC version of the patchset on THP refcounting redesign. I've cleaned up my todo list and I consider it feature-complete. The goal of patchset is to make refcounting on THP pages cheaper with simpler semantics and allow the same THP compound page to be mapped with PMD and PTEs. This is required to get reasonable THP-pagecache implementation. With the new refcounting design it's much easier to protect against split_huge_page(): simple reference on a page will make you the deal. It makes gup_fast() implementation simpler and doesn't require special-case in futex code to handle tail THP pages. It should improve THP utilization over the system since splitting THP in one process doesn't necessary lead to splitting the page in all other processes have the page mapped. = Design overview = The main reason why we can't map THP with 4k is how refcounting on THP designed. It built around two requirements: - split of huge page should never fail; - we can't change interface of get_user_page(); To be able to split huge page at any point we have to track which tail page was pinned. It leads to tricky and expensive get_page() on tail pages and also occupy tail_page->_mapcount. Most split_huge_page*() users want PMD to be split into table of PTEs and don't care whether compound page is going to be split or not. The plan is: - allow split_huge_page() to fail if the page is pinned. It's trivial to split non-pinned page and it doesn't require tail page refcounting, so tail_page->_mapcount is free to be reused. - introduce new routine -- split_huge_pmd() -- to split PMD into table of PTEs. It splits only one PMD, not touching other PMDs the page is mapped with or underlying compound page. Unlike new split_huge_page(), split_huge_pmd() never fails. Fortunately, we have only few places where split_huge_page() is needed: swap out, memory failure, migration, KSM. And all of them can handle split_huge_page() fail. In new scheme we use page->_mapcount is used to account how many time the page is mapped with PTEs. We have separate compound_mapcount() to count mappings with PMD. page_mapcount() returns sum of PTE and PMD mappings of the page. Introducing split_huge_pmd() effectively allows THP to be mapped with 4k. It may be a surprise to some code to see a PTE which points to tail page or VMA start/end in the middle of compound page. munmap() part of THP will split PMD, but doesn't split the huge page. In order to take memory consuption under control we put partially unmapped huge page on per-zone list, which would be drained on first shrink_zone() call. This way we also avoid unnecessary split_huge_page() on exit(2) if a THP belong to more than one VMA. = Patches overview = Patch 1: Move split_huge_page code around. Preparation for future changes. Patches 2-3: Make PageAnon() and PG_locked related helpers to look on head page if tail page is passed. It's required since pte_page() can now point to tail page. It's likely that we need to change other pageflags-related helpers too, but I haven't step on any other yet. Patch 4: With PTE-mapeed THP, rmap cannot rely on PageTransHuge() check to decide if map small page or THP. We need to get the info from caller. Patch 5: We need to look on all subpages of compound page to calculate correct PSS, because they can have different mapcount. Patch 6: Store mapcount for compound pages separately: in the first tail page ->mapping. Patch 7: Adjust conditions when we can re-use the page on write-protection fault. Patch 8: FOLL_SPLIT should be handled on PTE level too. Patch 9: Split all pages in mlocked VMA. We would need to look on this again later. Patch 10: Make khugepaged aware about PTE-mapped huge pages. Patch 11: split_huge_page_pmd() to split_huge_pmd() to reflect that page is not going to be split, only PMD. Patch 12: Temporary make split_huge_page() to return -EBUSY on all split requests. This allows to drop tail-page refcounting and change implementation of split_huge_pmd() to split PMD to table of PTEs without splitting compound page. Patch 13: New THP_SPLIT_* vmstats. Patch 14: Implement new split_huge_page() which fails if the page is pinned. For now, we rely on compound_lock() to make page counts stable. Patches 15-16: Drop infrastructure for handling PMD splitting. We don't use it anymore in split_huge_page(). For now we only remove it from generic code and x86. I'll cleanup other architectures later. Patch 17: Remove ugly special case if futex happened to be in tail THP page. With new refcounting it much easier to protect against split. Patches 18-20: Replaces compound_lock with migration entries as mechanism to freeze page counts on split_huge_page(). We don't need compound_lock anymore. It makes get_page()/put_page() on tail pages faster. Patch 21: Handle partial unmap of THP. We put partially unmapped huge page on per-zone list, which would be drained on first shrink_zone() call. This way we also avoid unnecessary split_huge_page() on exit(2) if a THP belong to more than one VMA. Patch 22: Make memcg aware about new refcounting. Validation needed. Patch 23: Fix never-succeed split_huge_page() inside KSM machinery. Patch 24: Documentation update. I was focused on stability so far and don't have performance numbers yet. I've run mm tests from LTP: all pass. Trinity doesn't crash patched kernel for me. I would appreciate any feedback on the patchset: in form of code review or testing. The patchset also available on git: git://git.kernel.org/pub/scm/linux/kernel/git/kas/linux.git thp/refcounting/v3 Comments? Kirill A. Shutemov (24): thp: cluster split_huge_page* code together mm: change PageAnon() and page_anon_vma() to work on tail pages mm: avoid PG_locked on tail pages rmap: add argument to charge compound page mm, proc: adjust PSS calculation mm: store mapcount for compound page separately mm, thp: adjust conditions when we can reuse the page on WP fault mm: adjust FOLL_SPLIT for new refcounting thp, mlock: do not allow huge pages in mlocked area khugepaged: ignore pmd tables with THP mapped with ptes thp: rename split_huge_page_pmd() to split_huge_pmd() thp: PMD splitting without splitting compound page mm, vmstats: new THP splitting event thp: implement new split_huge_page() mm, thp: remove infrastructure for handling splitting PMDs x86, thp: remove infrastructure for handling splitting PMDs futex, thp: remove special case for THP in get_futex_key thp, mm: split_huge_page(): caller need to lock page thp, mm: use migration entries to freeze page counts on split mm, thp: remove compound_lock thp: introduce deferred_split_huge_page() memcg: adjust to support new THP refcounting ksm: split huge pages on follow_page() thp: update documentation Documentation/vm/transhuge.txt | 100 ++-- arch/mips/mm/gup.c | 4 - arch/powerpc/mm/hugetlbpage.c | 13 +- arch/powerpc/mm/subpage-prot.c | 2 +- arch/s390/mm/gup.c | 13 +- arch/sparc/mm/gup.c | 14 +- arch/x86/include/asm/pgtable.h | 9 - arch/x86/include/asm/pgtable_types.h | 2 - arch/x86/kernel/vm86_32.c | 6 +- arch/x86/mm/gup.c | 17 +- arch/x86/mm/pgtable.c | 14 - fs/proc/task_mmu.c | 51 ++- include/asm-generic/pgtable.h | 5 - include/linux/huge_mm.h | 40 +- include/linux/hugetlb_inline.h | 9 +- include/linux/memcontrol.h | 16 +- include/linux/migrate.h | 3 + include/linux/mm.h | 125 +---- include/linux/mm_types.h | 20 +- include/linux/mmzone.h | 5 + include/linux/page-flags.h | 15 +- include/linux/pagemap.h | 14 +- include/linux/rmap.h | 19 +- include/linux/swap.h | 3 +- include/linux/vm_event_item.h | 4 +- kernel/events/uprobes.c | 11 +- kernel/futex.c | 61 +-- mm/debug.c | 8 +- mm/filemap.c | 9 +- mm/gup.c | 89 ++-- mm/huge_memory.c | 857 ++++++++++++++++++----------------- mm/hugetlb.c | 8 +- mm/internal.h | 57 +-- mm/ksm.c | 60 +-- mm/madvise.c | 2 +- mm/memcontrol.c | 76 +--- mm/memory-failure.c | 12 +- mm/memory.c | 64 +-- mm/mempolicy.c | 2 +- mm/migrate.c | 20 +- mm/mincore.c | 2 +- mm/mlock.c | 3 + mm/mprotect.c | 2 +- mm/mremap.c | 2 +- mm/page_alloc.c | 13 +- mm/pagewalk.c | 2 +- mm/pgtable-generic.c | 14 - mm/rmap.c | 121 +++-- mm/shmem.c | 21 +- mm/slub.c | 2 + mm/swap.c | 260 ++--------- mm/swapfile.c | 16 +- mm/vmscan.c | 3 + mm/vmstat.c | 4 +- 54 files changed, 975 insertions(+), 1349 deletions(-) -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/