linux-kernel - [PATCH v3 0/2] mm,thp: Add filemap_huge

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Date:   Wed, 31 Jul 2019 02:25:11 -0600
From:   William Kucharski <william.kucharski@...cle.com>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Song Liu <songliubraving@...com>,
        Bob Kasten <robert.a.kasten@...el.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        William Kucharski <william.kucharski@...cle.com>,
        Chad Mynhier <chad.mynhier@...cle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Johannes Weiner <jweiner@...com>,
        Matthew Wilcox <willy@...radead.org>
Subject: [PATCH v3 0/2] mm,thp: Add filemap_huge_fault() for THP

This set of patches is the first step towards a mechanism for automatically
mapping read-only text areas of appropriate size and alignment to THPs
whenever possible.

For now, the central routine, filemap_huge_fault(), amd various support
routines are only included if the experimental kernel configuration option

	RO_EXEC_FILEMAP_HUGE_FAULT_THP

is enabled.

This is because filemap_huge_fault() is dependent upon the
address_space_operations vector readpage() pointing to a routine that will
read and fill an entire large page at a time without poulluting the page
cache with PAGESIZE entries for the large page being mapped or performing
readahead that would pollute the page cache entries for succeeding large
pages. Unfortunately, there is no good way to determine how many bytes
were read by readpage(). At present, if filemap_huge_fault() were to call
a conventional readpage() routine, it would only fill the first PAGESIZE
bytes of the large page, which is definitely NOT the desired behavior.

However, by making the code available now it is hoped that filesystem
maintainers who have pledged to provide such a mechanism will do so more
rapidly.

The first part of the patch adds an order field to __page_cache_alloc(),
allowing callers to directly request page cache pages of various sizes.
This code was provided by Matthew Wilcox.

The second part of the patch implements the filemap_huge_fault() mechanism
as described above.

Changes since v2:
1. FGP changes were pulled out to enable submission as an independent
   patch
2. Inadvertent tab spacing and comment changes were reverted

Changes since v1:
1. Fix improperly generated patch for v1 PATCH 1/2

Matthew Wilcox (1):
  mm: Allow the page cache to allocate large pages

William Kucharski (1):
  Add filemap_huge_fault() to attempt to satisfy page faults on
    memory-mapped read-only text pages using THP when possible.

 fs/afs/dir.c            |   2 +-
 fs/btrfs/compression.c  |   2 +-
 fs/cachefiles/rdwr.c    |   4 +-
 fs/ceph/addr.c          |   2 +-
 fs/ceph/file.c          |   2 +-
 include/linux/huge_mm.h |  16 +-
 include/linux/mm.h      |   6 +
 include/linux/pagemap.h |  10 +-
 mm/Kconfig              |  15 ++
 mm/filemap.c            | 320 ++++++++++++++++++++++++++++++++++++++--
 mm/huge_memory.c        |   3 +
 mm/mmap.c               |  36 ++++-
 mm/readahead.c          |   2 +-
 mm/rmap.c               |   8 +
 net/ceph/pagelist.c     |   4 +-
 net/ceph/pagevec.c      |   2 +-
 16 files changed, 401 insertions(+), 33 deletions(-)

-- 
2.21.0