linux-stable/include/linux/rbtree.h

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/*
Red Black Trees
(C) 1999 Andrea Arcangeli <andrea@suse.de>
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
linux/include/linux/rbtree.h
To use rbtrees you'll have to implement your own insert and search cores.
This will avoid us to use callbacks and to drop drammatically performances.
I know it's not the cleaner way, but in C (not in C++) to get
performances and genericity...
rbtree: reference Documentation/rbtree.txt for usage instructions I recently started looking at the rbtree code (with an eye towards improving the augmented rbtree support, but I haven't gotten there yet). I noticed a lot of possible speed improvements, which I am now proposing in this patch set. Patches 1-4 are preparatory: remove internal functions from rbtree.h so that users won't be tempted to use them instead of the documented APIs, clean up some incorrect usages I've noticed (in particular, with the recently added fs/proc/proc_sysctl.c rbtree usage), reference the documentation so that people have one less excuse to miss it, etc. Patch 5 is a small module I wrote to check the rbtree performance. It creates 100 nodes with random keys and repeatedly inserts and erases them from an rbtree. Additionally, it has code to check for rbtree invariants after each insert or erase operation. Patches 6-12 is where the rbtree optimizations are done, and they touch only that one file, lib/rbtree.c . I am getting good results out of these - in my small benchmark doing rbtree insertion (including search) and erase, I'm seeing a 30% runtime reduction on Sandybridge E5, which is more than I initially thought would be possible. (the results aren't as impressive on my two other test hosts though, AMD barcelona and Intel Westmere, where I am seeing 14% runtime reduction only). The code size - both source (ommiting comments) and compiled - is also shorter after these changes. However, I do admit that the updated code is more arduous to read - one big reason for that is the removal of the tree rotation helpers, which added some overhead but also made it easier to reason about things locally. Overall, I believe this is an acceptable compromise, given that this code doesn't get modified very often, and that I have good tests for it. Upon Peter's suggestion, I added comments showing the rtree configuration before every rotation. I think they help; however it's still best to have a copy of the cormen/leiserson/rivest book when digging into this code. This patch: reference Documentation/rbtree.txt for usage instructions include/linux/rbtree.h included some basic usage instructions, while Documentation/rbtree.txt had some more complete and easier to follow instructions. Replacing the former with a reference to the latter. Signed-off-by: Michel Lespinasse <walken@google.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Acked-by: David Woodhouse <David.Woodhouse@intel.com> Cc: Rik van Riel <riel@redhat.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Daniel Santos <daniel.santos@pobox.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:30:28 +00:00
See Documentation/rbtree.txt for documentation and samples.
*/
#ifndef _LINUX_RBTREE_H
#define _LINUX_RBTREE_H
#include <linux/kernel.h>
#include <linux/stddef.h>
rbtree: Make lockless searches non-fatal Change the insert and erase code such that lockless searches are non-fatal. In and of itself an rbtree cannot be correctly searched while in-modification, we can however provide weaker guarantees that will allow the rbtree to be used in conjunction with other techniques, such as latches; see 9b0fd802e8c0 ("seqcount: Add raw_write_seqcount_latch()"). For this to work we need the following guarantees from the rbtree code: 1) a lockless reader must not see partial stores, this would allow it to observe nodes that are invalid memory. 2) there must not be (temporary) loops in the tree structure in the modifier's program order, this would cause a lookup which interrupts the modifier to get stuck indefinitely. For 1) we must use WRITE_ONCE() for all updates to the tree structure; in particular this patch only does rb_{left,right} as those are the only element required for simple searches. It generates slightly worse code, probably because volatile. But in pointer chasing heavy code a few instructions more should not matter. For 2) I have carefully audited the code and drawn every intermediate link state and not found a loop. Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: David Woodhouse <David.Woodhouse@intel.com> Cc: Rik van Riel <riel@redhat.com> Reviewed-by: Michel Lespinasse <walken@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
2015-05-27 01:39:36 +00:00
#include <linux/rcupdate.h>
struct rb_node {
unsigned long __rb_parent_color;
struct rb_node *rb_right;
struct rb_node *rb_left;
} __attribute__((aligned(sizeof(long))));
/* The alignment might seem pointless, but allegedly CRIS needs it */
struct rb_root {
struct rb_node *rb_node;
};
#define rb_parent(r) ((struct rb_node *)((r)->__rb_parent_color & ~3))
#define RB_ROOT (struct rb_root) { NULL, }
#define rb_entry(ptr, type, member) container_of(ptr, type, member)
#define RB_EMPTY_ROOT(root) (READ_ONCE((root)->rb_node) == NULL)
rbtree: empty nodes have no color Empty nodes have no color. We can make use of this property to simplify the code emitted by the RB_EMPTY_NODE and RB_CLEAR_NODE macros. Also, we can get rid of the rb_init_node function which had been introduced by commit 88d19cf37952 ("timers: Add rb_init_node() to allow for stack allocated rb nodes") to avoid some issue with the empty node's color not being initialized. I'm not sure what the RB_EMPTY_NODE checks in rb_prev() / rb_next() are doing there, though. axboe introduced them in commit 10fd48f2376d ("rbtree: fixed reversed RB_EMPTY_NODE and rb_next/prev"). The way I see it, the 'empty node' abstraction is only used by rbtree users to flag nodes that they haven't inserted in any rbtree, so asking the predecessor or successor of such nodes doesn't make any sense. One final rb_init_node() caller was recently added in sysctl code to implement faster sysctl name lookups. This code doesn't make use of RB_EMPTY_NODE at all, and from what I could see it only called rb_init_node() under the mistaken assumption that such initialization was required before node insertion. [sfr@canb.auug.org.au: fix net/ceph/osd_client.c build] Signed-off-by: Michel Lespinasse <walken@google.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Acked-by: David Woodhouse <David.Woodhouse@intel.com> Cc: Rik van Riel <riel@redhat.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Daniel Santos <daniel.santos@pobox.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: John Stultz <john.stultz@linaro.org> Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:30:32 +00:00
/* 'empty' nodes are nodes that are known not to be inserted in an rbtree */
#define RB_EMPTY_NODE(node) \
((node)->__rb_parent_color == (unsigned long)(node))
#define RB_CLEAR_NODE(node) \
((node)->__rb_parent_color = (unsigned long)(node))
extern void rb_insert_color(struct rb_node *, struct rb_root *);
extern void rb_erase(struct rb_node *, struct rb_root *);
rbtree: faster augmented rbtree manipulation Introduce new augmented rbtree APIs that allow minimal recalculation of augmented node information. A new callback is added to the rbtree insertion and erase rebalancing functions, to be called on each tree rotations. Such rotations preserve the subtree's root augmented value, but require recalculation of the one child that was previously located at the subtree root. In the insertion case, the handcoded search phase must be updated to maintain the augmented information on insertion, and then the rbtree coloring/rebalancing algorithms keep it up to date. In the erase case, things are more complicated since it is library code that manipulates the rbtree in order to remove internal nodes. This requires a couple additional callbacks to copy a subtree's augmented value when a new root is stitched in, and to recompute augmented values down the ancestry path when a node is removed from the tree. In order to preserve maximum speed for the non-augmented case, we provide two versions of each tree manipulation function. rb_insert_augmented() is the augmented equivalent of rb_insert_color(), and rb_erase_augmented() is the augmented equivalent of rb_erase(). Signed-off-by: Michel Lespinasse <walken@google.com> Acked-by: Rik van Riel <riel@redhat.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: David Woodhouse <dwmw2@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:31:17 +00:00
/* Find logical next and previous nodes in a tree */
extern struct rb_node *rb_next(const struct rb_node *);
extern struct rb_node *rb_prev(const struct rb_node *);
extern struct rb_node *rb_first(const struct rb_root *);
extern struct rb_node *rb_last(const struct rb_root *);
rbtree: add postorder iteration functions Postorder iteration yields all of a node's children prior to yielding the node itself, and this particular implementation also avoids examining the leaf links in a node after that node has been yielded. In what I expect will be its most common usage, postorder iteration allows the deletion of every node in an rbtree without modifying the rbtree nodes (no _requirement_ that they be nulled) while avoiding referencing child nodes after they have been "deleted" (most commonly, freed). I have only updated zswap to use this functionality at this point, but numerous bits of code (most notably in the filesystem drivers) use a hand rolled postorder iteration that NULLs child links as it traverses the tree. Each of those instances could be replaced with this common implementation. 1 & 2 add rbtree postorder iteration functions. 3 adds testing of the iteration to the rbtree runtime tests 4 allows building the rbtree runtime tests as builtins 5 updates zswap. This patch: Add postorder iteration functions for rbtree. These are useful for safely freeing an entire rbtree without modifying the tree at all. Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com> Reviewed-by: Seth Jennings <sjenning@linux.vnet.ibm.com> Cc: David Woodhouse <David.Woodhouse@intel.com> Cc: Rik van Riel <riel@redhat.com> Cc: Michel Lespinasse <walken@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-09-11 21:25:10 +00:00
/* Postorder iteration - always visit the parent after its children */
extern struct rb_node *rb_first_postorder(const struct rb_root *);
extern struct rb_node *rb_next_postorder(const struct rb_node *);
/* Fast replacement of a single node without remove/rebalance/add/rebalance */
rbtree: Make lockless searches non-fatal Change the insert and erase code such that lockless searches are non-fatal. In and of itself an rbtree cannot be correctly searched while in-modification, we can however provide weaker guarantees that will allow the rbtree to be used in conjunction with other techniques, such as latches; see 9b0fd802e8c0 ("seqcount: Add raw_write_seqcount_latch()"). For this to work we need the following guarantees from the rbtree code: 1) a lockless reader must not see partial stores, this would allow it to observe nodes that are invalid memory. 2) there must not be (temporary) loops in the tree structure in the modifier's program order, this would cause a lookup which interrupts the modifier to get stuck indefinitely. For 1) we must use WRITE_ONCE() for all updates to the tree structure; in particular this patch only does rb_{left,right} as those are the only element required for simple searches. It generates slightly worse code, probably because volatile. But in pointer chasing heavy code a few instructions more should not matter. For 2) I have carefully audited the code and drawn every intermediate link state and not found a loop. Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: David Woodhouse <David.Woodhouse@intel.com> Cc: Rik van Riel <riel@redhat.com> Reviewed-by: Michel Lespinasse <walken@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
2015-05-27 01:39:36 +00:00
extern void rb_replace_node(struct rb_node *victim, struct rb_node *new,
struct rb_root *root);
extern void rb_replace_node_rcu(struct rb_node *victim, struct rb_node *new,
struct rb_root *root);
rbtree: Make lockless searches non-fatal Change the insert and erase code such that lockless searches are non-fatal. In and of itself an rbtree cannot be correctly searched while in-modification, we can however provide weaker guarantees that will allow the rbtree to be used in conjunction with other techniques, such as latches; see 9b0fd802e8c0 ("seqcount: Add raw_write_seqcount_latch()"). For this to work we need the following guarantees from the rbtree code: 1) a lockless reader must not see partial stores, this would allow it to observe nodes that are invalid memory. 2) there must not be (temporary) loops in the tree structure in the modifier's program order, this would cause a lookup which interrupts the modifier to get stuck indefinitely. For 1) we must use WRITE_ONCE() for all updates to the tree structure; in particular this patch only does rb_{left,right} as those are the only element required for simple searches. It generates slightly worse code, probably because volatile. But in pointer chasing heavy code a few instructions more should not matter. For 2) I have carefully audited the code and drawn every intermediate link state and not found a loop. Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: David Woodhouse <David.Woodhouse@intel.com> Cc: Rik van Riel <riel@redhat.com> Reviewed-by: Michel Lespinasse <walken@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
2015-05-27 01:39:36 +00:00
static inline void rb_link_node(struct rb_node *node, struct rb_node *parent,
struct rb_node **rb_link)
{
node->__rb_parent_color = (unsigned long)parent;
node->rb_left = node->rb_right = NULL;
*rb_link = node;
}
rbtree: Make lockless searches non-fatal Change the insert and erase code such that lockless searches are non-fatal. In and of itself an rbtree cannot be correctly searched while in-modification, we can however provide weaker guarantees that will allow the rbtree to be used in conjunction with other techniques, such as latches; see 9b0fd802e8c0 ("seqcount: Add raw_write_seqcount_latch()"). For this to work we need the following guarantees from the rbtree code: 1) a lockless reader must not see partial stores, this would allow it to observe nodes that are invalid memory. 2) there must not be (temporary) loops in the tree structure in the modifier's program order, this would cause a lookup which interrupts the modifier to get stuck indefinitely. For 1) we must use WRITE_ONCE() for all updates to the tree structure; in particular this patch only does rb_{left,right} as those are the only element required for simple searches. It generates slightly worse code, probably because volatile. But in pointer chasing heavy code a few instructions more should not matter. For 2) I have carefully audited the code and drawn every intermediate link state and not found a loop. Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: David Woodhouse <David.Woodhouse@intel.com> Cc: Rik van Riel <riel@redhat.com> Reviewed-by: Michel Lespinasse <walken@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
2015-05-27 01:39:36 +00:00
static inline void rb_link_node_rcu(struct rb_node *node, struct rb_node *parent,
struct rb_node **rb_link)
{
node->__rb_parent_color = (unsigned long)parent;
node->rb_left = node->rb_right = NULL;
rcu_assign_pointer(*rb_link, node);
}
#define rb_entry_safe(ptr, type, member) \
({ typeof(ptr) ____ptr = (ptr); \
____ptr ? rb_entry(____ptr, type, member) : NULL; \
})
/**
rbtree: clarify documentation of rbtree_postorder_for_each_entry_safe() I noticed that commit a20135ffbc44 ("writeback: don't drain bdi_writeback_congested on bdi destruction") added a usage of rbtree_postorder_for_each_entry_safe() in mm/backing-dev.c which appears to try to rb_erase() elements from an rbtree while iterating over it using rbtree_postorder_for_each_entry_safe(). Doing this will cause random nodes to be missed by the iteration because rb_erase() may rebalance the tree, changing the ordering that we're trying to iterate over. The previous documentation for rbtree_postorder_for_each_entry_safe() wasn't clear that this wasn't allowed, it was taken from the docs for list_for_each_entry_safe(), where erasing isn't a problem due to list_del() not reordering. Explicitly warn developers about this potential pit-fall. Note that I haven't fixed the actual issue that (it appears) the commit referenced above introduced (not familiar enough with that code). In general (and in this case), the patterns to follow are: - switch to rb_first() + rb_erase(), don't use rbtree_postorder_for_each_entry_safe(). - keep the postorder iteration and don't rb_erase() at all. Instead just clear the fields of rb_node & cgwb_congested_tree as required by other users of those structures. [akpm@linux-foundation.org: tweak comments] Signed-off-by: Cody P Schafer <dev@codyps.com> Cc: John de la Garza <john@jjdev.com> Cc: Michel Lespinasse <walken@google.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: Tejun Heo <tj@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-11-07 00:31:28 +00:00
* rbtree_postorder_for_each_entry_safe - iterate in post-order over rb_root of
* given type allowing the backing memory of @pos to be invalidated
*
* @pos: the 'type *' to use as a loop cursor.
* @n: another 'type *' to use as temporary storage
* @root: 'rb_root *' of the rbtree.
* @field: the name of the rb_node field within 'type'.
rbtree: clarify documentation of rbtree_postorder_for_each_entry_safe() I noticed that commit a20135ffbc44 ("writeback: don't drain bdi_writeback_congested on bdi destruction") added a usage of rbtree_postorder_for_each_entry_safe() in mm/backing-dev.c which appears to try to rb_erase() elements from an rbtree while iterating over it using rbtree_postorder_for_each_entry_safe(). Doing this will cause random nodes to be missed by the iteration because rb_erase() may rebalance the tree, changing the ordering that we're trying to iterate over. The previous documentation for rbtree_postorder_for_each_entry_safe() wasn't clear that this wasn't allowed, it was taken from the docs for list_for_each_entry_safe(), where erasing isn't a problem due to list_del() not reordering. Explicitly warn developers about this potential pit-fall. Note that I haven't fixed the actual issue that (it appears) the commit referenced above introduced (not familiar enough with that code). In general (and in this case), the patterns to follow are: - switch to rb_first() + rb_erase(), don't use rbtree_postorder_for_each_entry_safe(). - keep the postorder iteration and don't rb_erase() at all. Instead just clear the fields of rb_node & cgwb_congested_tree as required by other users of those structures. [akpm@linux-foundation.org: tweak comments] Signed-off-by: Cody P Schafer <dev@codyps.com> Cc: John de la Garza <john@jjdev.com> Cc: Michel Lespinasse <walken@google.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: Tejun Heo <tj@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-11-07 00:31:28 +00:00
*
* rbtree_postorder_for_each_entry_safe() provides a similar guarantee as
* list_for_each_entry_safe() and allows the iteration to continue independent
* of changes to @pos by the body of the loop.
*
* Note, however, that it cannot handle other modifications that re-order the
* rbtree it is iterating over. This includes calling rb_erase() on @pos, as
* rb_erase() may rebalance the tree, causing us to miss some nodes.
*/
#define rbtree_postorder_for_each_entry_safe(pos, n, root, field) \
for (pos = rb_entry_safe(rb_first_postorder(root), typeof(*pos), field); \
pos && ({ n = rb_entry_safe(rb_next_postorder(&pos->field), \
typeof(*pos), field); 1; }); \
pos = n)
#endif /* _LINUX_RBTREE_H */