From 6328650bb4d854a7dc1498d1c0048b838b0d340c Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Wed, 3 Aug 2011 16:21:18 -0700 Subject: [PATCH] radix_tree: exceptional entries and indices A patchset to extend tmpfs to MAX_LFS_FILESIZE by abandoning its peculiar swap vector, instead keeping a file's swap entries in the same radix tree as its struct page pointers: thus saving memory, and simplifying its code and locking. This patch: The radix_tree is used by several subsystems for different purposes. A major use is to store the struct page pointers of a file's pagecache for memory management. But what if mm wanted to store something other than page pointers there too? The low bit of a radix_tree entry is already used to denote an indirect pointer, for internal use, and the unlikely radix_tree_deref_retry() case. Define the next bit as denoting an exceptional entry, and supply inline functions radix_tree_exception() to return non-0 in either unlikely case, and radix_tree_exceptional_entry() to return non-0 in the second case. If a subsystem already uses radix_tree with that bit set, no problem: it does not affect internal workings at all, but is defined for the convenience of those storing well-aligned pointers in the radix_tree. The radix_tree_gang_lookups have an implicit assumption that the caller can deduce the offset of each entry returned e.g. by the page->index of a struct page. But that may not be feasible for some kinds of item to be stored there. radix_tree_gang_lookup_slot() allow for an optional indices argument, output array in which to return those offsets. The same could be added to other radix_tree_gang_lookups, but for now keep it to the only one for which we need it. Signed-off-by: Hugh Dickins Acked-by: Rik van Riel Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/radix-tree.h | 36 +++++++++++++++++++++++++++++++++--- lib/radix-tree.c | 29 +++++++++++++++++++---------- mm/filemap.c | 4 ++-- 3 files changed, 54 insertions(+), 15 deletions(-) diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h index 23241c2fecce..b7edf8251455 100644 --- a/include/linux/radix-tree.h +++ b/include/linux/radix-tree.h @@ -39,7 +39,15 @@ * when it is shrunk, before we rcu free the node. See shrink code for * details. */ -#define RADIX_TREE_INDIRECT_PTR 1 +#define RADIX_TREE_INDIRECT_PTR 1 +/* + * A common use of the radix tree is to store pointers to struct pages; + * but shmem/tmpfs needs also to store swap entries in the same tree: + * those are marked as exceptional entries to distinguish them. + * EXCEPTIONAL_ENTRY tests the bit, EXCEPTIONAL_SHIFT shifts content past it. + */ +#define RADIX_TREE_EXCEPTIONAL_ENTRY 2 +#define RADIX_TREE_EXCEPTIONAL_SHIFT 2 #define radix_tree_indirect_to_ptr(ptr) \ radix_tree_indirect_to_ptr((void __force *)(ptr)) @@ -173,6 +181,28 @@ static inline int radix_tree_deref_retry(void *arg) return unlikely((unsigned long)arg & RADIX_TREE_INDIRECT_PTR); } +/** + * radix_tree_exceptional_entry - radix_tree_deref_slot gave exceptional entry? + * @arg: value returned by radix_tree_deref_slot + * Returns: 0 if well-aligned pointer, non-0 if exceptional entry. + */ +static inline int radix_tree_exceptional_entry(void *arg) +{ + /* Not unlikely because radix_tree_exception often tested first */ + return (unsigned long)arg & RADIX_TREE_EXCEPTIONAL_ENTRY; +} + +/** + * radix_tree_exception - radix_tree_deref_slot returned either exception? + * @arg: value returned by radix_tree_deref_slot + * Returns: 0 if well-aligned pointer, non-0 if either kind of exception. + */ +static inline int radix_tree_exception(void *arg) +{ + return unlikely((unsigned long)arg & + (RADIX_TREE_INDIRECT_PTR | RADIX_TREE_EXCEPTIONAL_ENTRY)); +} + /** * radix_tree_replace_slot - replace item in a slot * @pslot: pointer to slot, returned by radix_tree_lookup_slot @@ -194,8 +224,8 @@ void *radix_tree_delete(struct radix_tree_root *, unsigned long); unsigned int radix_tree_gang_lookup(struct radix_tree_root *root, void **results, unsigned long first_index, unsigned int max_items); -unsigned int -radix_tree_gang_lookup_slot(struct radix_tree_root *root, void ***results, +unsigned int radix_tree_gang_lookup_slot(struct radix_tree_root *root, + void ***results, unsigned long *indices, unsigned long first_index, unsigned int max_items); unsigned long radix_tree_next_hole(struct radix_tree_root *root, unsigned long index, unsigned long max_scan); diff --git a/lib/radix-tree.c b/lib/radix-tree.c index 7ea2e033d715..348eaefbed74 100644 --- a/lib/radix-tree.c +++ b/lib/radix-tree.c @@ -823,8 +823,8 @@ unsigned long radix_tree_prev_hole(struct radix_tree_root *root, EXPORT_SYMBOL(radix_tree_prev_hole); static unsigned int -__lookup(struct radix_tree_node *slot, void ***results, unsigned long index, - unsigned int max_items, unsigned long *next_index) +__lookup(struct radix_tree_node *slot, void ***results, unsigned long *indices, + unsigned long index, unsigned int max_items, unsigned long *next_index) { unsigned int nr_found = 0; unsigned int shift, height; @@ -857,12 +857,16 @@ __lookup(struct radix_tree_node *slot, void ***results, unsigned long index, /* Bottom level: grab some items */ for (i = index & RADIX_TREE_MAP_MASK; i < RADIX_TREE_MAP_SIZE; i++) { - index++; if (slot->slots[i]) { - results[nr_found++] = &(slot->slots[i]); - if (nr_found == max_items) + results[nr_found] = &(slot->slots[i]); + if (indices) + indices[nr_found] = index; + if (++nr_found == max_items) { + index++; goto out; + } } + index++; } out: *next_index = index; @@ -918,8 +922,8 @@ radix_tree_gang_lookup(struct radix_tree_root *root, void **results, if (cur_index > max_index) break; - slots_found = __lookup(node, (void ***)results + ret, cur_index, - max_items - ret, &next_index); + slots_found = __lookup(node, (void ***)results + ret, NULL, + cur_index, max_items - ret, &next_index); nr_found = 0; for (i = 0; i < slots_found; i++) { struct radix_tree_node *slot; @@ -944,6 +948,7 @@ EXPORT_SYMBOL(radix_tree_gang_lookup); * radix_tree_gang_lookup_slot - perform multiple slot lookup on radix tree * @root: radix tree root * @results: where the results of the lookup are placed + * @indices: where their indices should be placed (but usually NULL) * @first_index: start the lookup from this key * @max_items: place up to this many items at *results * @@ -958,7 +963,8 @@ EXPORT_SYMBOL(radix_tree_gang_lookup); * protection, radix_tree_deref_slot may fail requiring a retry. */ unsigned int -radix_tree_gang_lookup_slot(struct radix_tree_root *root, void ***results, +radix_tree_gang_lookup_slot(struct radix_tree_root *root, + void ***results, unsigned long *indices, unsigned long first_index, unsigned int max_items) { unsigned long max_index; @@ -974,6 +980,8 @@ radix_tree_gang_lookup_slot(struct radix_tree_root *root, void ***results, if (first_index > 0) return 0; results[0] = (void **)&root->rnode; + if (indices) + indices[0] = 0; return 1; } node = indirect_to_ptr(node); @@ -987,8 +995,9 @@ radix_tree_gang_lookup_slot(struct radix_tree_root *root, void ***results, if (cur_index > max_index) break; - slots_found = __lookup(node, results + ret, cur_index, - max_items - ret, &next_index); + slots_found = __lookup(node, results + ret, + indices ? indices + ret : NULL, + cur_index, max_items - ret, &next_index); ret += slots_found; if (next_index == 0) break; diff --git a/mm/filemap.c b/mm/filemap.c index 867d40222ec7..b83aebfd0a00 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -840,7 +840,7 @@ unsigned find_get_pages(struct address_space *mapping, pgoff_t start, rcu_read_lock(); restart: nr_found = radix_tree_gang_lookup_slot(&mapping->page_tree, - (void ***)pages, start, nr_pages); + (void ***)pages, NULL, start, nr_pages); ret = 0; for (i = 0; i < nr_found; i++) { struct page *page; @@ -903,7 +903,7 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index, rcu_read_lock(); restart: nr_found = radix_tree_gang_lookup_slot(&mapping->page_tree, - (void ***)pages, index, nr_pages); + (void ***)pages, NULL, index, nr_pages); ret = 0; for (i = 0; i < nr_found; i++) { struct page *page; -- GitLab