linux.git/mm/filemap.c, branch v5.4-rc2

mm,thp: avoid writes to file with THP in pagecache

2019-09-24T22:54:11+00:00

In previous patch, an application could put part of its text section in
THP via madvise().  These THPs will be protected from writes when the
application is still running (TXTBSY).  However, after the application
exits, the file is available for writes.

This patch avoids writes to file THP by dropping page cache for the file
when the file is open for write.  A new counter nr_thps is added to struct
address_space.  In do_dentry_open(), if the file is open for write and
nr_thps is non-zero, we drop page cache for the whole file.

Link: http://lkml.kernel.org/r/20190801184244.3169074-8-songliubraving@fb.com
Signed-off-by: Song Liu 
Reported-by: kbuild test robot 
Acked-by: Rik van Riel 
Acked-by: Kirill A. Shutemov 
Acked-by: Johannes Weiner 
Cc: Hillf Danton 
Cc: Hugh Dickins 
Cc: William Kucharski 
Cc: Oleg Nesterov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm,thp: add read-only THP support for (non-shmem) FS

2019-09-24T22:54:11+00:00

This patch is (hopefully) the first step to enable THP for non-shmem
filesystems.

This patch enables an application to put part of its text sections to THP
via madvise, for example:

    madvise((void *)0x600000, 0x200000, MADV_HUGEPAGE);

We tried to reuse the logic for THP on tmpfs.

Currently, write is not supported for non-shmem THP.  khugepaged will only
process vma with VM_DENYWRITE.  sys_mmap() ignores VM_DENYWRITE requests
(see ksys_mmap_pgoff).  The only way to create vma with VM_DENYWRITE is
execve().  This requirement limits non-shmem THP to text sections.

The next patch will handle writes, which would only happen when the all
the vmas with VM_DENYWRITE are unmapped.

An EXPERIMENTAL config, READ_ONLY_THP_FOR_FS, is added to gate this
feature.

[songliubraving@fb.com: fix build without CONFIG_SHMEM]
  Link: http://lkml.kernel.org/r/F53407FB-96CC-42E8-9862-105C92CC2B98@fb.com
[songliubraving@fb.com: fix double unlock in collapse_file()]
  Link: http://lkml.kernel.org/r/B960CBFA-8EFC-4DA4-ABC5-1977FFF2CA57@fb.com
Link: http://lkml.kernel.org/r/20190801184244.3169074-7-songliubraving@fb.com
Signed-off-by: Song Liu 
Acked-by: Rik van Riel 
Acked-by: Kirill A. Shutemov 
Acked-by: Johannes Weiner 
Cc: Stephen Rothwell 
Cc: Dan Carpenter 
Cc: Hillf Danton 
Cc: Hugh Dickins 
Cc: William Kucharski 
Cc: Oleg Nesterov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

filemap: update offset check in filemap_fault()

2019-09-24T22:54:11+00:00

With THP, current check of offset:

    VM_BUG_ON_PAGE(page->index != offset, page);

is no longer accurate. Update it to:

    VM_BUG_ON_PAGE(page_to_pgoff(page) != offset, page);

Link: http://lkml.kernel.org/r/20190801184244.3169074-4-songliubraving@fb.com
Signed-off-by: Song Liu 
Acked-by: Rik van Riel 
Acked-by: Kirill A. Shutemov 
Acked-by: Johannes Weiner 
Cc: Hillf Danton 
Cc: Hugh Dickins 
Cc: William Kucharski 
Cc: Oleg Nesterov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

filemap: check compound_head(page)->mapping in pagecache_get_page()

2019-09-24T22:54:11+00:00

Similar to previous patch, pagecache_get_page() avoids race condition with
truncate by checking page->mapping == mapping.  This does not work for
compound pages.  This patch let it check compound_head(page)->mapping
instead.

Link: http://lkml.kernel.org/r/20190801184244.3169074-3-songliubraving@fb.com
Signed-off-by: Song Liu 
Suggested-by: Johannes Weiner 
Acked-by: Johannes Weiner 
Cc: Hillf Danton 
Cc: Hugh Dickins 
Cc: Kirill A. Shutemov 
Cc: Rik van Riel 
Cc: William Kucharski 
Cc: Oleg Nesterov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

filemap: check compound_head(page)->mapping in filemap_fault()

2019-09-24T22:54:10+00:00

Patch series "Enable THP for text section of non-shmem files", v10;

This patchset follows up discussion at LSF/MM 2019.  The motivation is to
put text section of an application in THP, and thus reduces iTLB miss rate
and improves performance.  Both Facebook and Oracle showed strong
interests to this feature.

To make reviews easier, this set aims a mininal valid product.  Current
version of the work does not have any changes to file system specific
code.  This comes with some limitations (discussed later).

This set enables an application to "hugify" its text section by simply
running something like:

          madvise(0x600000, 0x80000, MADV_HUGEPAGE);

Before this call, the /proc//maps looks like:

    00400000-074d0000 r-xp 00000000 00:27 2006927     app

After this call, part of the text section is split out and mapped to
THP:

    00400000-00425000 r-xp 00000000 00:27 2006927     app
    00600000-00e00000 r-xp 00200000 00:27 2006927     app   <<< on THP
    00e00000-074d0000 r-xp 00a00000 00:27 2006927     app

Limitations:

1. This only works for text section (vma with VM_DENYWRITE).
2. Original limitation #2 is removed in v3.

We gated this feature with an experimental config, READ_ONLY_THP_FOR_FS.
Once we get better support on the write path, we can remove the config and
enable it by default.

Tested cases:
1. Tested with btrfs and ext4.
2. Tested with real work application (memcache like caching service).
3. Tested with "THP aware uprobe":
   https://patchwork.kernel.org/project/linux-mm/list/?series=131339

This patch (of 7):

Currently, filemap_fault() avoids race condition with truncate by checking
page->mapping == mapping.  This does not work for compound pages.  This
patch let it check compound_head(page)->mapping instead.

Link: http://lkml.kernel.org/r/20190801184244.3169074-2-songliubraving@fb.com
Signed-off-by: Song Liu 
Acked-by: Rik van Riel 
Acked-by: Kirill A. Shutemov 
Acked-by: Johannes Weiner 
Cc: William Kucharski 
Cc: Hillf Danton 
Cc: Hugh Dickins 
Cc: Oleg Nesterov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: page cache: store only head pages in i_pages

2019-09-24T22:54:08+00:00

Transparent Huge Pages are currently stored in i_pages as pointers to
consecutive subpages.  This patch changes that to storing consecutive
pointers to the head page in preparation for storing huge pages more
efficiently in i_pages.

Large parts of this are "inspired" by Kirill's patch
https://lore.kernel.org/lkml/20170126115819.58875-2-kirill.shutemov@linux.intel.com/

Kirill and Huang Ying contributed several fixes.

[willy@infradead.org: use compound_nr, squish uninit-var warning]
Link: http://lkml.kernel.org/r/20190731210400.7419-1-willy@infradead.org
Signed-off-by: Matthew Wilcox 
Acked-by: Jan Kara 
Reviewed-by: Kirill Shutemov 
Reviewed-by: Song Liu 
Tested-by: Song Liu 
Tested-by: William Kucharski 
Reviewed-by: William Kucharski 
Tested-by: Qian Cai 
Tested-by: Mikhail Gavrilov 
Cc: Hugh Dickins 
Cc: Chris Wilson 
Cc: Song Liu 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/filemap.c: rewrite mapping_needs_writeback in less fancy manner

2019-09-24T22:54:08+00:00

This actually checks that writeback is needed or in progress.

Link: http://lkml.kernel.org/r/156378817069.1087.1302816672037672488.stgit@buzz
Signed-off-by: Konstantin Khlebnikov 
Reviewed-by: Andrew Morton 
Cc: Tejun Heo 
Cc: Jens Axboe 
Cc: Johannes Weiner 
Cc: Jan Kara 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/filemap.c: don't initiate writeback if mapping has no dirty pages

2019-09-24T22:54:08+00:00

Functions like filemap_write_and_wait_range() should do nothing if inode
has no dirty pages or pages currently under writeback.  But they anyway
construct struct writeback_control and this does some atomic operations if
CONFIG_CGROUP_WRITEBACK=y - on fast path it locks inode->i_lock and
updates state of writeback ownership, on slow path might be more work.
Current this path is safely avoided only when inode mapping has no pages.

For example generic_file_read_iter() calls filemap_write_and_wait_range()
at each O_DIRECT read - pretty hot path.

This patch skips starting new writeback if mapping has no dirty tags set.
If writeback is already in progress filemap_write_and_wait_range() will
wait for it.

Link: http://lkml.kernel.org/r/156378816804.1087.8607636317907921438.stgit@buzz
Signed-off-by: Konstantin Khlebnikov 
Reviewed-by: Jan Kara 
Cc: Tejun Heo 
Cc: Jens Axboe 
Cc: Johannes Weiner 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: introduce compound_nr()

2019-09-24T22:54:08+00:00

Replace 1 << compound_order(page) with compound_nr(page).  Minor
improvements in readability.

Link: http://lkml.kernel.org/r/20190721104612.19120-4-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) 
Reviewed-by: Andrew Morton 
Reviewed-by: Ira Weiny 
Acked-by: Kirill A. Shutemov 
Cc: Michal Hocko 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

vfs: don't allow writes to swap files

2019-08-20T14:55:16+00:00

Don't let userspace write to an active swap file because the kernel
effectively has a long term lease on the storage and things could get
seriously corrupted if we let this happen.

Signed-off-by: Darrick J. Wong 
Reviewed-by: Christoph Hellwig