linux-toradex.git/include/linux/radix-tree.h, branch v4.6-rc2

radix-tree,shmem: introduce radix_tree_iter_next()

2016-03-17T22:09:34+00:00

shmem likes to occasionally drop the lock, schedule, then reacqire the
lock and continue with the iteration from the last place it left off.
This is currently done with a pretty ugly goto.  Introduce
radix_tree_iter_next() and use it throughout shmem.c.

[koct9i@gmail.com: fix bug in radix_tree_iter_next() for tagged iteration]
Signed-off-by: Matthew Wilcox 
Cc: Hugh Dickins 
Signed-off-by: Konstantin Khlebnikov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

radix_tree: add support for multi-order entries

2016-03-17T22:09:34+00:00

With huge pages, it is convenient to have the radix tree be able to
return an entry that covers multiple indices.  Previous attempts to deal
with the problem have involved inserting N duplicate entries, which is a
waste of memory and leads to problems trying to handle aliased tags, or
probing the tree multiple times to find alternative entries which might
cover the requested index.

This approach inserts one canonical entry into the tree for a given
range of indices, and may also insert other entries in order to ensure
that lookups find the canonical entry.

This solution only tolerates inserting powers of two that are greater
than the fanout of the tree.  If we wish to expand the radix tree's
abilities to support large-ish pages that is less than the fanout at the
penultimate level of the tree, then we would need to add one more step
in lookup to ensure that any sibling nodes in the final level of the
tree are dereferenced and we return the canonical entry that they
reference.

Signed-off-by: Matthew Wilcox 
Cc: Johannes Weiner 
Cc: Matthew Wilcox 
Cc: "Kirill A. Shutemov" 
Cc: Ross Zwisler 
Cc: Hugh Dickins 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

radix-tree: add an explicit include of bitops.h

2016-03-17T22:09:34+00:00

The radix-tree header uses the __ffs() function, which is defined in
bitops.h.  The current kernel headers implicitly include bitops.h, but
the userspace test harness does not.

Signed-off-by: Matthew Wilcox 
Cc: Johannes Weiner 
Cc: Matthew Wilcox 
Cc: "Kirill A. Shutemov" 
Cc: Ross Zwisler 
Cc: Hugh Dickins 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

radix-tree: fix oops after radix_tree_iter_retry

2016-02-06T02:10:40+00:00

Helper radix_tree_iter_retry() resets next_index to the current index.
In following radix_tree_next_slot current chunk size becomes zero.  This
isn't checked and it tries to dereference null pointer in slot.

Tagged iterator is fine because retry happens only at slot 0 where tag
bitmask in iter->tags is filled with single bit.

Fixes: 46437f9a554f ("radix-tree: fix race in gang lookup")
Signed-off-by: Konstantin Khlebnikov 
Cc: Matthew Wilcox 
Cc: Hugh Dickins 
Cc: Ohad Ben-Cohen 
Cc: Jeremiah Mahler 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

radix-tree: fix race in gang lookup

2016-02-03T16:28:43+00:00

If the indirect_ptr bit is set on a slot, that indicates we need to redo
the lookup.  Introduce a new function radix_tree_iter_retry() which
forces the loop to retry the lookup by setting 'slot' to NULL and
turning the iterator back to point at the problematic entry.

This is a pretty rare problem to hit at the moment; the lookup has to
race with a grow of the radix tree from a height of 0.  The consequences
of hitting this race are that gang lookup could return a pointer to a
radix_tree_node instead of a pointer to whatever the user had inserted
in the tree.

Fixes: cebbd29e1c2f ("radix-tree: rewrite gang lookup using iterator")
Signed-off-by: Matthew Wilcox 
Cc: Hugh Dickins 
Cc: Ohad Ben-Cohen 
Cc: Konstantin Khlebnikov 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

dax: support dirty DAX entries in radix tree

2016-01-23T01:02:18+00:00

Add support for tracking dirty DAX entries in the struct address_space
radix tree.  This tree is already used for dirty page writeback, and it
already supports the use of exceptional (non struct page*) entries.

In order to properly track dirty DAX pages we will insert new
exceptional entries into the radix tree that represent dirty DAX PTE or
PMD pages.  These exceptional entries will also contain the writeback
addresses for the PTE or PMD faults that we can use at fsync/msync time.

There are currently two types of exceptional entries (shmem and shadow)
that can be placed into the radix tree, and this adds a third.  We rely
on the fact that only one type of exceptional entry can be found in a
given radix tree based on its usage.  This happens for free with DAX vs
shmem but we explicitly prevent shadow entries from being added to radix
trees for DAX mappings.

The only shadow entries that would be generated for DAX radix trees
would be to track zero page mappings that were created for holes.  These
pages would receive minimal benefit from having shadow entries, and the
choice to have only one type of exceptional entry in a given radix tree
makes the logic simpler both in clear_exceptional_entry() and in the
rest of DAX.

Signed-off-by: Ross Zwisler 
Cc: "H. Peter Anvin" 
Cc: "J. Bruce Fields" 
Cc: "Theodore Ts'o" 
Cc: Alexander Viro 
Cc: Andreas Dilger 
Cc: Dave Chinner 
Cc: Ingo Molnar 
Cc: Jan Kara 
Cc: Jeff Layton 
Cc: Matthew Wilcox 
Cc: Thomas Gleixner 
Cc: Dan Williams 
Cc: Matthew Wilcox 
Cc: Dave Hansen 
Cc: Hugh Dickins 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

include/linux/radix-tree.h: fix error in docs about locks

2016-01-21T01:09:18+00:00

This text refers to the "first 7 functions", which was correct when
written but became incorrect when Johannes Weiner added another function
to the list in 139e561660fe ("lib: radix_tree: tree node interface").

Change the text to correctly refer to the first 8 functions.

Signed-off-by: Adam Barth 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: keep page cache radix tree nodes in check

2014-04-03T23:21:01+00:00

Previously, page cache radix tree nodes were freed after reclaim emptied
out their page pointers.  But now reclaim stores shadow entries in their
place, which are only reclaimed when the inodes themselves are
reclaimed.  This is problematic for bigger files that are still in use
after they have a significant amount of their cache reclaimed, without
any of those pages actually refaulting.  The shadow entries will just
sit there and waste memory.  In the worst case, the shadow entries will
accumulate until the machine runs out of memory.

To get this under control, the VM will track radix tree nodes
exclusively containing shadow entries on a per-NUMA node list.  Per-NUMA
rather than global because we expect the radix tree nodes themselves to
be allocated node-locally and we want to reduce cross-node references of
otherwise independent cache workloads.  A simple shrinker will then
reclaim these nodes on memory pressure.

A few things need to be stored in the radix tree node to implement the
shadow node LRU and allow tree deletions coming from the list:

1. There is no index available that would describe the reverse path
   from the node up to the tree root, which is needed to perform a
   deletion.  To solve this, encode in each node its offset inside the
   parent.  This can be stored in the unused upper bits of the same
   member that stores the node's height at no extra space cost.

2. The number of shadow entries needs to be counted in addition to the
   regular entries, to quickly detect when the node is ready to go to
   the shadow node LRU list.  The current entry count is an unsigned
   int but the maximum number of entries is 64, so a shadow counter
   can easily be stored in the unused upper bits.

3. Tree modification needs tree lock and tree root, which are located
   in the address space, so store an address_space backpointer in the
   node.  The parent pointer of the node is in a union with the 2-word
   rcu_head, so the backpointer comes at no extra cost as well.

4. The node needs to be linked to an LRU list, which requires a list
   head inside the node.  This does increase the size of the node, but
   it does not change the number of objects that fit into a slab page.

[akpm@linux-foundation.org: export the right function]
Signed-off-by: Johannes Weiner 
Reviewed-by: Rik van Riel 
Reviewed-by: Minchan Kim 
Cc: Andrea Arcangeli 
Cc: Bob Liu 
Cc: Christoph Hellwig 
Cc: Dave Chinner 
Cc: Greg Thelen 
Cc: Hugh Dickins 
Cc: Jan Kara 
Cc: KOSAKI Motohiro 
Cc: Luigi Semenzato 
Cc: Mel Gorman 
Cc: Metin Doslu 
Cc: Michel Lespinasse 
Cc: Ozgun Erdogan 
Cc: Peter Zijlstra 
Cc: Roman Gushchin 
Cc: Ryan Mallon 
Cc: Tejun Heo 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

lib: radix_tree: tree node interface

2014-04-03T23:21:01+00:00

Make struct radix_tree_node part of the public interface and provide API
functions to create, look up, and delete whole nodes.  Refactor the
existing insert, look up, delete functions on top of these new node
primitives.

This will allow the VM to track and garbage collect page cache radix
tree nodes.

[sasha.levin@oracle.com: return correct error code on insertion failure]
Signed-off-by: Johannes Weiner 
Reviewed-by: Rik van Riel 
Cc: Andrea Arcangeli 
Cc: Bob Liu 
Cc: Christoph Hellwig 
Cc: Dave Chinner 
Cc: Greg Thelen 
Cc: Hugh Dickins 
Cc: Jan Kara 
Cc: KOSAKI Motohiro 
Cc: Luigi Semenzato 
Cc: Mel Gorman 
Cc: Metin Doslu 
Cc: Michel Lespinasse 
Cc: Ozgun Erdogan 
Cc: Peter Zijlstra 
Cc: Roman Gushchin 
Cc: Ryan Mallon 
Cc: Tejun Heo 
Cc: Vlastimil Babka 
Signed-off-by: Sasha Levin 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: filemap: move radix tree hole searching here

2014-04-03T23:21:00+00:00

The radix tree hole searching code is only used for page cache, for
example the readahead code trying to get a a picture of the area
surrounding a fault.

It sufficed to rely on the radix tree definition of holes, which is
"empty tree slot".  But this is about to change, though, as shadow page
descriptors will be stored in the page cache after the actual pages get
evicted from memory.

Move the functions over to mm/filemap.c and make them native page cache
operations, where they can later be adapted to handle the new definition
of "page cache hole".

Signed-off-by: Johannes Weiner 
Reviewed-by: Rik van Riel 
Reviewed-by: Minchan Kim 
Acked-by: Mel Gorman 
Cc: Andrea Arcangeli 
Cc: Bob Liu 
Cc: Christoph Hellwig 
Cc: Dave Chinner 
Cc: Greg Thelen 
Cc: Hugh Dickins 
Cc: Jan Kara 
Cc: KOSAKI Motohiro 
Cc: Luigi Semenzato 
Cc: Metin Doslu 
Cc: Michel Lespinasse 
Cc: Ozgun Erdogan 
Cc: Peter Zijlstra 
Cc: Roman Gushchin 
Cc: Ryan Mallon 
Cc: Tejun Heo 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds