![Chris Mason](/assets/img/avatar_default.png)
There are two main users of the extent_map tree. The first is regular file inodes, where it is evenly spread between readers and writers. The second is the chunk allocation tree, which maps blocks from logical addresses to phyiscal ones, and it is 99.99% reads. The mapping tree is a point of lock contention during heavy IO workloads, so this commit switches things to a rw lock. Signed-off-by: Chris Mason <chris.mason@oracle.com>
336 lines
8.3 KiB
C
336 lines
8.3 KiB
C
#include <linux/err.h>
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#include <linux/gfp.h>
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#include <linux/slab.h>
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#include <linux/module.h>
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#include <linux/spinlock.h>
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#include <linux/hardirq.h>
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#include "extent_map.h"
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static struct kmem_cache *extent_map_cache;
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int __init extent_map_init(void)
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{
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extent_map_cache = kmem_cache_create("extent_map",
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sizeof(struct extent_map), 0,
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SLAB_RECLAIM_ACCOUNT | SLAB_MEM_SPREAD, NULL);
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if (!extent_map_cache)
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return -ENOMEM;
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return 0;
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}
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void extent_map_exit(void)
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{
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if (extent_map_cache)
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kmem_cache_destroy(extent_map_cache);
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}
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/**
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* extent_map_tree_init - initialize extent map tree
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* @tree: tree to initialize
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* @mask: flags for memory allocations during tree operations
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*
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* Initialize the extent tree @tree. Should be called for each new inode
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* or other user of the extent_map interface.
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*/
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void extent_map_tree_init(struct extent_map_tree *tree, gfp_t mask)
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{
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tree->map.rb_node = NULL;
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rwlock_init(&tree->lock);
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}
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/**
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* alloc_extent_map - allocate new extent map structure
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* @mask: memory allocation flags
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*
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* Allocate a new extent_map structure. The new structure is
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* returned with a reference count of one and needs to be
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* freed using free_extent_map()
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*/
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struct extent_map *alloc_extent_map(gfp_t mask)
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{
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struct extent_map *em;
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em = kmem_cache_alloc(extent_map_cache, mask);
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if (!em || IS_ERR(em))
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return em;
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em->in_tree = 0;
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em->flags = 0;
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atomic_set(&em->refs, 1);
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return em;
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}
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/**
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* free_extent_map - drop reference count of an extent_map
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* @em: extent map beeing releasead
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*
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* Drops the reference out on @em by one and free the structure
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* if the reference count hits zero.
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*/
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void free_extent_map(struct extent_map *em)
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{
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if (!em)
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return;
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WARN_ON(atomic_read(&em->refs) == 0);
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if (atomic_dec_and_test(&em->refs)) {
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WARN_ON(em->in_tree);
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kmem_cache_free(extent_map_cache, em);
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}
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}
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static struct rb_node *tree_insert(struct rb_root *root, u64 offset,
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struct rb_node *node)
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{
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struct rb_node **p = &root->rb_node;
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struct rb_node *parent = NULL;
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struct extent_map *entry;
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while (*p) {
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parent = *p;
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entry = rb_entry(parent, struct extent_map, rb_node);
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WARN_ON(!entry->in_tree);
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if (offset < entry->start)
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p = &(*p)->rb_left;
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else if (offset >= extent_map_end(entry))
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p = &(*p)->rb_right;
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else
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return parent;
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}
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entry = rb_entry(node, struct extent_map, rb_node);
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entry->in_tree = 1;
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rb_link_node(node, parent, p);
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rb_insert_color(node, root);
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return NULL;
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}
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/*
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* search through the tree for an extent_map with a given offset. If
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* it can't be found, try to find some neighboring extents
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*/
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static struct rb_node *__tree_search(struct rb_root *root, u64 offset,
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struct rb_node **prev_ret,
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struct rb_node **next_ret)
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{
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struct rb_node *n = root->rb_node;
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struct rb_node *prev = NULL;
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struct rb_node *orig_prev = NULL;
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struct extent_map *entry;
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struct extent_map *prev_entry = NULL;
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while (n) {
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entry = rb_entry(n, struct extent_map, rb_node);
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prev = n;
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prev_entry = entry;
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WARN_ON(!entry->in_tree);
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if (offset < entry->start)
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n = n->rb_left;
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else if (offset >= extent_map_end(entry))
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n = n->rb_right;
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else
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return n;
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}
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if (prev_ret) {
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orig_prev = prev;
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while (prev && offset >= extent_map_end(prev_entry)) {
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prev = rb_next(prev);
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prev_entry = rb_entry(prev, struct extent_map, rb_node);
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}
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*prev_ret = prev;
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prev = orig_prev;
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}
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if (next_ret) {
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prev_entry = rb_entry(prev, struct extent_map, rb_node);
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while (prev && offset < prev_entry->start) {
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prev = rb_prev(prev);
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prev_entry = rb_entry(prev, struct extent_map, rb_node);
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}
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*next_ret = prev;
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}
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return NULL;
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}
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/*
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* look for an offset in the tree, and if it can't be found, return
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* the first offset we can find smaller than 'offset'.
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*/
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static inline struct rb_node *tree_search(struct rb_root *root, u64 offset)
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{
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struct rb_node *prev;
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struct rb_node *ret;
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ret = __tree_search(root, offset, &prev, NULL);
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if (!ret)
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return prev;
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return ret;
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}
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/* check to see if two extent_map structs are adjacent and safe to merge */
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static int mergable_maps(struct extent_map *prev, struct extent_map *next)
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{
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if (test_bit(EXTENT_FLAG_PINNED, &prev->flags))
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return 0;
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/*
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* don't merge compressed extents, we need to know their
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* actual size
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*/
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if (test_bit(EXTENT_FLAG_COMPRESSED, &prev->flags))
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return 0;
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if (extent_map_end(prev) == next->start &&
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prev->flags == next->flags &&
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prev->bdev == next->bdev &&
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((next->block_start == EXTENT_MAP_HOLE &&
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prev->block_start == EXTENT_MAP_HOLE) ||
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(next->block_start == EXTENT_MAP_INLINE &&
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prev->block_start == EXTENT_MAP_INLINE) ||
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(next->block_start == EXTENT_MAP_DELALLOC &&
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prev->block_start == EXTENT_MAP_DELALLOC) ||
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(next->block_start < EXTENT_MAP_LAST_BYTE - 1 &&
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next->block_start == extent_map_block_end(prev)))) {
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return 1;
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}
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return 0;
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}
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/**
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* add_extent_mapping - add new extent map to the extent tree
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* @tree: tree to insert new map in
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* @em: map to insert
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*
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* Insert @em into @tree or perform a simple forward/backward merge with
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* existing mappings. The extent_map struct passed in will be inserted
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* into the tree directly, with an additional reference taken, or a
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* reference dropped if the merge attempt was sucessfull.
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*/
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int add_extent_mapping(struct extent_map_tree *tree,
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struct extent_map *em)
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{
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int ret = 0;
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struct extent_map *merge = NULL;
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struct rb_node *rb;
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struct extent_map *exist;
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exist = lookup_extent_mapping(tree, em->start, em->len);
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if (exist) {
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free_extent_map(exist);
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ret = -EEXIST;
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goto out;
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}
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rb = tree_insert(&tree->map, em->start, &em->rb_node);
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if (rb) {
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ret = -EEXIST;
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goto out;
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}
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atomic_inc(&em->refs);
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if (em->start != 0) {
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rb = rb_prev(&em->rb_node);
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if (rb)
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merge = rb_entry(rb, struct extent_map, rb_node);
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if (rb && mergable_maps(merge, em)) {
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em->start = merge->start;
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em->len += merge->len;
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em->block_len += merge->block_len;
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em->block_start = merge->block_start;
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merge->in_tree = 0;
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rb_erase(&merge->rb_node, &tree->map);
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free_extent_map(merge);
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}
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}
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rb = rb_next(&em->rb_node);
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if (rb)
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merge = rb_entry(rb, struct extent_map, rb_node);
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if (rb && mergable_maps(em, merge)) {
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em->len += merge->len;
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em->block_len += merge->len;
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rb_erase(&merge->rb_node, &tree->map);
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merge->in_tree = 0;
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free_extent_map(merge);
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}
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out:
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return ret;
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}
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/* simple helper to do math around the end of an extent, handling wrap */
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static u64 range_end(u64 start, u64 len)
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{
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if (start + len < start)
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return (u64)-1;
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return start + len;
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}
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/**
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* lookup_extent_mapping - lookup extent_map
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* @tree: tree to lookup in
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* @start: byte offset to start the search
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* @len: length of the lookup range
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*
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* Find and return the first extent_map struct in @tree that intersects the
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* [start, len] range. There may be additional objects in the tree that
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* intersect, so check the object returned carefully to make sure that no
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* additional lookups are needed.
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*/
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struct extent_map *lookup_extent_mapping(struct extent_map_tree *tree,
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u64 start, u64 len)
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{
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struct extent_map *em;
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struct rb_node *rb_node;
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struct rb_node *prev = NULL;
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struct rb_node *next = NULL;
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u64 end = range_end(start, len);
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rb_node = __tree_search(&tree->map, start, &prev, &next);
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if (!rb_node && prev) {
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em = rb_entry(prev, struct extent_map, rb_node);
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if (end > em->start && start < extent_map_end(em))
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goto found;
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}
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if (!rb_node && next) {
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em = rb_entry(next, struct extent_map, rb_node);
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if (end > em->start && start < extent_map_end(em))
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goto found;
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}
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if (!rb_node) {
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em = NULL;
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goto out;
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}
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if (IS_ERR(rb_node)) {
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em = ERR_PTR(PTR_ERR(rb_node));
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goto out;
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}
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em = rb_entry(rb_node, struct extent_map, rb_node);
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if (end > em->start && start < extent_map_end(em))
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goto found;
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em = NULL;
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goto out;
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found:
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atomic_inc(&em->refs);
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out:
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return em;
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}
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/**
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* remove_extent_mapping - removes an extent_map from the extent tree
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* @tree: extent tree to remove from
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* @em: extent map beeing removed
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*
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* Removes @em from @tree. No reference counts are dropped, and no checks
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* are done to see if the range is in use
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*/
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int remove_extent_mapping(struct extent_map_tree *tree, struct extent_map *em)
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{
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int ret = 0;
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WARN_ON(test_bit(EXTENT_FLAG_PINNED, &em->flags));
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rb_erase(&em->rb_node, &tree->map);
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em->in_tree = 0;
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return ret;
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}
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