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radix-tree: improve multiorder iterators

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This fixes several interlinked problems with the iterators in the
presence of multiorder entries.

1. radix_tree_iter_next() would only advance by one slot, which would
   result in the iterators returning the same entry more than once if
   there were sibling entries.

2. radix_tree_next_slot() could return an internal pointer instead of
   a user pointer if a tagged multiorder entry was immediately followed by
   an entry of lower order.

3. radix_tree_next_slot() expanded to a lot more code than it used to
   when multiorder support was compiled in.  And I wasn't comfortable with
   entry_to_node() being in a header file.

Fixing radix_tree_iter_next() for the presence of sibling entries
necessarily involves examining the contents of the radix tree, so we now
need to pass 'slot' to radix_tree_iter_next(), and we need to change the
calling convention so it is called *before* dropping the lock which
protects the tree.  Also rename it to radix_tree_iter_resume(), as some
people thought it was necessary to call radix_tree_iter_next() each time
around the loop.

radix_tree_next_slot() becomes closer to how it looked before multiorder
support was introduced.  It only checks to see if the next entry in the
chunk is a sibling entry or a pointer to a node; this should be rare
enough that handling this case out of line is not a performance impact
(and such impact is amortised by the fact that the entry we just
processed was a multiorder entry).  Also, radix_tree_next_slot() used to
force a new chunk lookup for untagged entries, which is more expensive
than the out of line sibling entry skipping.

Link: http://lkml.kernel.org/r/1480369871-5271-55-git-send-email-mawilcox@linuxonhyperv.com
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Tested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Matthew Wilcox
2016-12-14 15:08:49 -08:00
committed by Linus Torvalds
parent b35df27a39
commit 148deab223
9 changed files with 188 additions and 85 deletions
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6
mm/shmem.c
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@@ -661,8 +661,8 @@ unsigned long shmem_partial_swap_usage(struct address_space *mapping,
swapped++;
if (need_resched()) {
slot = radix_tree_iter_resume(slot, &iter);
cond_resched_rcu();
slot = radix_tree_iter_next(&iter);
}
}
@@ -2447,8 +2447,8 @@ static void shmem_tag_pins(struct address_space *mapping)
}
if (need_resched()) {
slot = radix_tree_iter_resume(slot, &iter);
cond_resched_rcu();
slot = radix_tree_iter_next(&iter);
}
}
rcu_read_unlock();
@@ -2517,8 +2517,8 @@ static int shmem_wait_for_pins(struct address_space *mapping)
spin_unlock_irq(&mapping->tree_lock);
continue_resched:
if (need_resched()) {
slot = radix_tree_iter_resume(slot, &iter);
cond_resched_rcu();
slot = radix_tree_iter_next(&iter);
}
}
rcu_read_unlock();