linux.git/mm/memory.c, branch v4.7-rc4

Merge tag 'dax-locking-for-4.7' of git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm

2016-05-27T03:00:28+00:00

Pull DAX locking updates from Ross Zwisler:
 "Filesystem DAX locking for 4.7

   - We use a bit in an exceptional radix tree entry as a lock bit and
     use it similarly to how page lock is used for normal faults.  This
     fixes races between hole instantiation and read faults of the same
     index.

   - Filesystem DAX PMD faults are disabled, and will be re-enabled when
     PMD locking is implemented"

* tag 'dax-locking-for-4.7' of git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm:
  dax: Remove i_mmap_lock protection
  dax: Use radix tree entry lock to protect cow faults
  dax: New fault locking
  dax: Allow DAX code to replace exceptional entries
  dax: Define DAX lock bit for radix tree exceptional entry
  dax: Make huge page handling depend of CONFIG_BROKEN
  dax: Fix condition for filling of PMD holes

mm: disable fault around on emulated access bit architecture

2016-05-21T00:58:30+00:00

fault_around aims to reduce minor faults of file-backed pages via
speculative ahead pte mapping and relying on readahead logic.  However,
on non-HW access bit architecture the benefit is highly limited because
they should emulate the young bit with minor faults for reclaim's page
aging algorithm.  IOW, we cannot reduce minor faults on those
architectures.

I did quick a test on my ARM machine.

512M file mmap sequential every word read on eSATA drive 4 times.
stddev is stable.

  = fault_around 4096 =
  elapsed time(usec): 6747645

  = fault_around 65536 =
  elapsed time(usec): 6709263

  0.5% gain.

Even when I tested it with eMMC there is no gain because I guess with
slow storage the major fault is the dominant factor.

Also, fault_around has the side effect of shrinking slab more
aggressively and causes higher vmpressure, so if such speculation fails,
it can evict slab more which can result in page I/O (e.g., inode cache).
In the end, it would make void any benefit of fault_around.

So let's make the default "disabled" on those architectures.

Link: http://lkml.kernel.org/r/20160518014229.GB21538@bbox
Signed-off-by: Minchan Kim 
Cc: Kirill A. Shutemov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: make faultaround produce old ptes

2016-05-21T00:58:30+00:00

Currently, faultaround code produces young pte.  This can screw up
vmscan behaviour[1], as it makes vmscan think that these pages are hot
and not push them out on first round.

During sparse file access faultaround gets more pages mapped and all of
them are young.  Under memory pressure, this makes vmscan swap out anon
pages instead, or to drop other page cache pages which otherwise stay
resident.

Modify faultaround to produce old ptes, so they can easily be reclaimed
under memory pressure.

This can to some extend defeat the purpose of faultaround on machines
without hardware accessed bit as it will not help us with reducing the
number of minor page faults.

We may want to disable faultaround on such machines altogether, but
that's subject for separate patchset.

Minchan:
 "I tested 512M mmap sequential word read test on non-HW access bit
  system (i.e., ARM) and confirmed it doesn't increase minor fault any
  more.

  old: 4096 fault_around
  minor fault: 131291
  elapsed time: 6747645 usec

  new: 65536 fault_around
  minor fault: 131291
  elapsed time: 6709263 usec

  0.56% benefit"

[1] https://lkml.kernel.org/r/1460992636-711-1-git-send-email-vinmenon@codeaurora.org

Link: http://lkml.kernel.org/r/1463488366-47723-1-git-send-email-kirill.shutemov@linux.intel.com
Signed-off-by: Kirill A. Shutemov 
Acked-by: Michal Hocko 
Acked-by: Minchan Kim 
Tested-by: Minchan Kim 
Acked-by: Rik van Riel 
Cc: Mel Gorman 
Cc: Michal Hocko 
Cc: Vinayak Menon 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: fix incorrect pfn passed to untrack_pfn() in remap_pfn_range()

2016-05-21T00:58:30+00:00

We use generic hooks in remap_pfn_range() to help archs to track pfnmap
regions.  The code is something like:

  int remap_pfn_range()
  {
	...
	track_pfn_remap(vma, &prot, pfn, addr, PAGE_ALIGN(size));
	...
	pfn -= addr >> PAGE_SHIFT;
	...
	untrack_pfn(vma, pfn, PAGE_ALIGN(size));
	...
  }

Here we can easily find the pfn is changed but not recovered before
untrack_pfn() is called.  That's incorrect.

There are no known runtime effects - this is from inspection.

Signed-off-by: Yongji Xie 
Cc: Kirill A. Shutemov 
Cc: Jerome Marchand 
Cc: Ingo Molnar 
Cc: Vlastimil Babka 
Cc: Dave Hansen 
Cc: Dan Williams 
Cc: Matthew Wilcox 
Cc: Andrea Arcangeli 
Cc: Michal Hocko 
Cc: Andy Lutomirski 
Cc: David Hildenbrand 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

dax: Remove i_mmap_lock protection

2016-05-19T21:28:40+00:00

Currently faults are protected against truncate by filesystem specific
i_mmap_sem and page lock in case of hole page. Cow faults are protected
DAX radix tree entry locking. So there's no need for i_mmap_lock in DAX
code. Remove it.

Reviewed-by: Ross Zwisler 
Signed-off-by: Jan Kara 
Signed-off-by: Ross Zwisler

dax: Use radix tree entry lock to protect cow faults

2016-05-19T21:27:49+00:00

When doing cow faults, we cannot directly fill in PTE as we do for other
faults as we rely on generic code to do proper accounting of the cowed page.
We also have no page to lock to protect against races with truncate as
other faults have and we need the protection to extend until the moment
generic code inserts cowed page into PTE thus at that point we have no
protection of fs-specific i_mmap_sem. So far we relied on using
i_mmap_lock for the protection however that is completely special to cow
faults. To make fault locking more uniform use DAX entry lock instead.

Reviewed-by: Ross Zwisler 
Signed-off-by: Jan Kara 
Signed-off-by: Ross Zwisler

mm: thp: calculate the mapcount correctly for THP pages during WP faults

2016-05-12T22:52:50+00:00

This will provide fully accuracy to the mapcount calculation in the
write protect faults, so page pinning will not get broken by false
positive copy-on-writes.

total_mapcount() isn't the right calculation needed in
reuse_swap_page(), so this introduces a page_trans_huge_mapcount()
that is effectively the full accurate return value for page_mapcount()
if dealing with Transparent Hugepages, however we only use the
page_trans_huge_mapcount() during COW faults where it strictly needed,
due to its higher runtime cost.

This also provide at practical zero cost the total_mapcount
information which is needed to know if we can still relocate the page
anon_vma to the local vma. If page_trans_huge_mapcount() returns 1 we
can reuse the page no matter if it's a pte or a pmd_trans_huge
triggering the fault, but we can only relocate the page anon_vma to
the local vma->anon_vma if we're sure it's only this "vma" mapping the
whole THP physical range.

Kirill A. Shutemov discovered the problem with moving the page
anon_vma to the local vma->anon_vma in a previous version of this
patch and another problem in the way page_move_anon_rmap() was called.

Andrew Morton discovered that CONFIG_SWAP=n wouldn't build in a
previous version, because reuse_swap_page must be a macro to call
page_trans_huge_mapcount from swap.h, so this uses a macro again
instead of an inline function. With this change at least it's a less
dangerous usage than it was before, because "page" is used only once
now, while with the previous code reuse_swap_page(page++) would have
called page_mapcount on page+1 and it would have increased page twice
instead of just once.

Dean Luick noticed an uninitialized variable that could result in a
rmap inefficiency for the non-THP case in a previous version.

Mike Marciniszyn said:

: Our RDMA tests are seeing an issue with memory locking that bisects to
: commit 61f5d698cc97 ("mm: re-enable THP")
:
: The test program registers two rather large MRs (512M) and RDMA
: writes data to a passive peer using the first and RDMA reads it back
: into the second MR and compares that data.  The sizes are chosen randomly
: between 0 and 1024 bytes.
:
: The test will get through a few (<= 4 iterations) and then gets a
: compare error.
:
: Tracing indicates the kernel logical addresses associated with the individual
: pages at registration ARE correct , the data in the "RDMA read response only"
: packets ARE correct.
:
: The "corruption" occurs when the packet crosse two pages that are not physically
: contiguous.   The second page reads back as zero in the program.
:
: It looks like the user VA at the point of the compare error no longer points to
: the same physical address as was registered.
:
: This patch totally resolves the issue!

Link: http://lkml.kernel.org/r/1462547040-1737-2-git-send-email-aarcange@redhat.com
Signed-off-by: Andrea Arcangeli 
Reviewed-by: "Kirill A. Shutemov" 
Reviewed-by: Dean Luick 
Tested-by: Alex Williamson 
Tested-by: Mike Marciniszyn 
Tested-by: Josh Collier 
Cc: Marc Haber 
Cc: 	[4.5]
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

huge pagecache: mmap_sem is unlocked when truncation splits pmd

2016-05-06T00:38:53+00:00

zap_pmd_range()'s CONFIG_DEBUG_VM !rwsem_is_locked(&mmap_sem) BUG() will
be invalid with huge pagecache, in whatever way it is implemented:
truncation of a hugely-mapped file to an unhugely-aligned size would
easily hit it.

(Although anon THP could in principle apply khugepaged to private file
mappings, which are not excluded by the MADV_HUGEPAGE restrictions, in
practice there's a vm_ops check which excludes them, so it never hits
this BUG() - there's no interface to "truncate" an anonymous mapping.)

We could complicate the test, to check i_mmap_rwsem also when there's a
vm_file; but my inclination was to make zap_pmd_range() more readable by
simply deleting this check.  A search has shown no report of the issue
in the years since commit e0897d75f0b2 ("mm, thp: print useful
information when mmap_sem is unlocked in zap_pmd_range") expanded it
from VM_BUG_ON() - though I cannot point to what commit I would say then
fixed the issue.

But there are a couple of other patches now floating around, neither yet
in the tree: let's agree to retain the check as a VM_BUG_ON_VMA(), as
Matthew Wilcox has done; but subject to a vma_is_anonymous() check, as
Kirill Shutemov has done.  And let's get this in, without waiting for
any particular huge pagecache implementation to reach the tree.

Matthew said "We can reproduce this BUG() in the current Linus tree with
DAX PMDs".

Signed-off-by: Hugh Dickins 
Tested-by: Matthew Wilcox 
Cc: "Kirill A. Shutemov" 
Cc: Andrea Arcangeli 
Cc: Andres Lagar-Cavilla 
Cc: Yang Shi 
Cc: Ning Qu 
Cc: Mel Gorman 
Cc: Andres Lagar-Cavilla 
Cc: Konstantin Khlebnikov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

numa: fix /proc//numa_maps for THP

2016-04-29T02:34:04+00:00

In gather_pte_stats() a THP pmd is cast into a pte, which is wrong
because the layouts may differ depending on the architecture.  On s390
this will lead to inaccurate numa_maps accounting in /proc because of
misguided pte_present() and pte_dirty() checks on the fake pte.

On other architectures pte_present() and pte_dirty() may work by chance,
but there may be an issue with direct-access (dax) mappings w/o
underlying struct pages when HAVE_PTE_SPECIAL is set and THP is
available.  In vm_normal_page() the fake pte will be checked with
pte_special() and because there is no "special" bit in a pmd, this will
always return false and the VM_PFNMAP | VM_MIXEDMAP checking will be
skipped.  On dax mappings w/o struct pages, an invalid struct page
pointer would then be returned that can crash the kernel.

This patch fixes the numa_maps THP handling by introducing new "_pmd"
variants of the can_gather_numa_stats() and vm_normal_page() functions.

Signed-off-by: Gerald Schaefer 
Cc: Naoya Horiguchi 
Cc: "Kirill A . Shutemov" 
Cc: Konstantin Khlebnikov 
Cc: Michal Hocko 
Cc: Vlastimil Babka 
Cc: Jerome Marchand 
Cc: Johannes Weiner 
Cc: Dave Hansen 
Cc: Mel Gorman 
Cc: Dan Williams 
Cc: Martin Schwidefsky 
Cc: Heiko Carstens 
Cc: Michael Holzheu 
Cc: 	[4.3+]
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm, fs: remove remaining PAGE_CACHE_* and page_cache_{get,release} usage

2016-04-04T17:41:08+00:00

Mostly direct substitution with occasional adjustment or removing
outdated comments.

Signed-off-by: Kirill A. Shutemov 
Acked-by: Michal Hocko 
Signed-off-by: Linus Torvalds