commit 8fc75643c5e14574c8be59b69182452ece28315a upstream
In order to use multi-index entries for huge pages in the page cache, we need to be able to split a multi-index entry (eg if a file is truncated in the middle of a huge page entry). This version does not support splitting more than one level of the tree at a time. This is an acceptable limitation for the page cache as we do not expect to support order-12 pages in the near future.
[akpm@linux-foundation.org: export xas_split_alloc() to modules] [willy@infradead.org: fix xarray split] Link: https://lkml.kernel.org/r/20200910175450.GV6583@casper.infradead.org [willy@infradead.org: fix xarray] Link: https://lkml.kernel.org/r/20201001233943.GW20115@casper.infradead.org
Signed-off-by: Matthew Wilcox (Oracle) willy@infradead.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Cc: "Kirill A . Shutemov" kirill@shutemov.name Cc: Qian Cai cai@lca.pw Cc: Song Liu songliubraving@fb.com Link: https://lkml.kernel.org/r/20200903183029.14930-3-willy@infradead.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org --- Documentation/core-api/xarray.rst | 16 +-- include/linux/xarray.h | 13 +++ lib/test_xarray.c | 44 ++++++++ lib/xarray.c | 168 ++++++++++++++++++++++++++++-- 4 files changed, 225 insertions(+), 16 deletions(-)
diff --git a/Documentation/core-api/xarray.rst b/Documentation/core-api/xarray.rst index fcedc5349ace..2ad3c1fce579 100644 --- a/Documentation/core-api/xarray.rst +++ b/Documentation/core-api/xarray.rst @@ -461,13 +461,15 @@ or iterations will move the index to the first index in the range. Each entry will only be returned once, no matter how many indices it occupies.
-Using xas_next() or xas_prev() with a multi-index xa_state -is not supported. Using either of these functions on a multi-index entry -will reveal sibling entries; these should be skipped over by the caller. - -Storing ``NULL`` into any index of a multi-index entry will set the entry -at every index to ``NULL`` and dissolve the tie. Splitting a multi-index -entry into entries occupying smaller ranges is not yet supported. +Using xas_next() or xas_prev() with a multi-index xa_state is not +supported. Using either of these functions on a multi-index entry will +reveal sibling entries; these should be skipped over by the caller. + +Storing ``NULL`` into any index of a multi-index entry will set the +entry at every index to ``NULL`` and dissolve the tie. A multi-index +entry can be split into entries occupying smaller ranges by calling +xas_split_alloc() without the xa_lock held, followed by taking the lock +and calling xas_split().
Functions and structures ======================== diff --git a/include/linux/xarray.h b/include/linux/xarray.h index 63185fe7cd6a..2903f25bff5e 100644 --- a/include/linux/xarray.h +++ b/include/linux/xarray.h @@ -1472,11 +1472,24 @@ void xas_create_range(struct xa_state *);
#ifdef CONFIG_XARRAY_MULTI int xa_get_order(struct xarray *, unsigned long index); +void xas_split(struct xa_state *, void *entry, unsigned int order); +void xas_split_alloc(struct xa_state *, void *entry, unsigned int order, gfp_t); #else static inline int xa_get_order(struct xarray *xa, unsigned long index) { return 0; } + +static inline void xas_split(struct xa_state *xas, void *entry, + unsigned int order) +{ + xas_store(xas, entry); +} + +static inline void xas_split_alloc(struct xa_state *xas, void *entry, + unsigned int order, gfp_t gfp) +{ +} #endif
/** diff --git a/lib/test_xarray.c b/lib/test_xarray.c index bdd4d7995f79..8262c3f05a5d 100644 --- a/lib/test_xarray.c +++ b/lib/test_xarray.c @@ -1503,6 +1503,49 @@ static noinline void check_store_range(struct xarray *xa) } }
+#ifdef CONFIG_XARRAY_MULTI +static void check_split_1(struct xarray *xa, unsigned long index, + unsigned int order) +{ + XA_STATE(xas, xa, index); + void *entry; + unsigned int i = 0; + + xa_store_order(xa, index, order, xa, GFP_KERNEL); + + xas_split_alloc(&xas, xa, order, GFP_KERNEL); + xas_lock(&xas); + xas_split(&xas, xa, order); + xas_unlock(&xas); + + xa_for_each(xa, index, entry) { + XA_BUG_ON(xa, entry != xa); + i++; + } + XA_BUG_ON(xa, i != 1 << order); + + xa_set_mark(xa, index, XA_MARK_0); + XA_BUG_ON(xa, !xa_get_mark(xa, index, XA_MARK_0)); + + xa_destroy(xa); +} + +static noinline void check_split(struct xarray *xa) +{ + unsigned int order; + + XA_BUG_ON(xa, !xa_empty(xa)); + + for (order = 1; order < 2 * XA_CHUNK_SHIFT; order++) { + check_split_1(xa, 0, order); + check_split_1(xa, 1UL << order, order); + check_split_1(xa, 3UL << order, order); + } +} +#else +static void check_split(struct xarray *xa) { } +#endif + static void check_align_1(struct xarray *xa, char *name) { int i; @@ -1729,6 +1772,7 @@ static int xarray_checks(void) check_store_range(&array); check_store_iter(&array); check_align(&xa0); + check_split(&array);
check_workingset(&array, 0); check_workingset(&array, 64); diff --git a/lib/xarray.c b/lib/xarray.c index 57b9c144f793..7d22b3059127 100644 --- a/lib/xarray.c +++ b/lib/xarray.c @@ -266,13 +266,14 @@ static void xa_node_free(struct xa_node *node) */ static void xas_destroy(struct xa_state *xas) { - struct xa_node *node = xas->xa_alloc; + struct xa_node *next, *node = xas->xa_alloc;
- if (!node) - return; - XA_NODE_BUG_ON(node, !list_empty(&node->private_list)); - kmem_cache_free(radix_tree_node_cachep, node); - xas->xa_alloc = NULL; + while (node) { + XA_NODE_BUG_ON(node, !list_empty(&node->private_list)); + next = rcu_dereference_raw(node->parent); + radix_tree_node_rcu_free(&node->rcu_head); + xas->xa_alloc = node = next; + } }
/** @@ -304,6 +305,7 @@ bool xas_nomem(struct xa_state *xas, gfp_t gfp) xas->xa_alloc = kmem_cache_alloc(radix_tree_node_cachep, gfp); if (!xas->xa_alloc) return false; + xas->xa_alloc->parent = NULL; XA_NODE_BUG_ON(xas->xa_alloc, !list_empty(&xas->xa_alloc->private_list)); xas->xa_node = XAS_RESTART; return true; @@ -339,6 +341,7 @@ static bool __xas_nomem(struct xa_state *xas, gfp_t gfp) } if (!xas->xa_alloc) return false; + xas->xa_alloc->parent = NULL; XA_NODE_BUG_ON(xas->xa_alloc, !list_empty(&xas->xa_alloc->private_list)); xas->xa_node = XAS_RESTART; return true; @@ -403,7 +406,7 @@ static unsigned long xas_size(const struct xa_state *xas) /* * Use this to calculate the maximum index that will need to be created * in order to add the entry described by @xas. Because we cannot store a - * multiple-index entry at index 0, the calculation is a little more complex + * multi-index entry at index 0, the calculation is a little more complex * than you might expect. */ static unsigned long xas_max(struct xa_state *xas) @@ -946,6 +949,153 @@ void xas_init_marks(const struct xa_state *xas) } EXPORT_SYMBOL_GPL(xas_init_marks);
+#ifdef CONFIG_XARRAY_MULTI +static unsigned int node_get_marks(struct xa_node *node, unsigned int offset) +{ + unsigned int marks = 0; + xa_mark_t mark = XA_MARK_0; + + for (;;) { + if (node_get_mark(node, offset, mark)) + marks |= 1 << (__force unsigned int)mark; + if (mark == XA_MARK_MAX) + break; + mark_inc(mark); + } + + return marks; +} + +static void node_set_marks(struct xa_node *node, unsigned int offset, + struct xa_node *child, unsigned int marks) +{ + xa_mark_t mark = XA_MARK_0; + + for (;;) { + if (marks & (1 << (__force unsigned int)mark)) { + node_set_mark(node, offset, mark); + if (child) + node_mark_all(child, mark); + } + if (mark == XA_MARK_MAX) + break; + mark_inc(mark); + } +} + +/** + * xas_split_alloc() - Allocate memory for splitting an entry. + * @xas: XArray operation state. + * @entry: New entry which will be stored in the array. + * @order: New entry order. + * @gfp: Memory allocation flags. + * + * This function should be called before calling xas_split(). + * If necessary, it will allocate new nodes (and fill them with @entry) + * to prepare for the upcoming split of an entry of @order size into + * entries of the order stored in the @xas. + * + * Context: May sleep if @gfp flags permit. + */ +void xas_split_alloc(struct xa_state *xas, void *entry, unsigned int order, + gfp_t gfp) +{ + unsigned int sibs = (1 << (order % XA_CHUNK_SHIFT)) - 1; + unsigned int mask = xas->xa_sibs; + + /* XXX: no support for splitting really large entries yet */ + if (WARN_ON(xas->xa_shift + 2 * XA_CHUNK_SHIFT < order)) + goto nomem; + if (xas->xa_shift + XA_CHUNK_SHIFT > order) + return; + + do { + unsigned int i; + void *sibling; + struct xa_node *node; + + node = kmem_cache_alloc(radix_tree_node_cachep, gfp); + if (!node) + goto nomem; + node->array = xas->xa; + for (i = 0; i < XA_CHUNK_SIZE; i++) { + if ((i & mask) == 0) { + RCU_INIT_POINTER(node->slots[i], entry); + sibling = xa_mk_sibling(0); + } else { + RCU_INIT_POINTER(node->slots[i], sibling); + } + } + RCU_INIT_POINTER(node->parent, xas->xa_alloc); + xas->xa_alloc = node; + } while (sibs-- > 0); + + return; +nomem: + xas_destroy(xas); + xas_set_err(xas, -ENOMEM); +} +EXPORT_SYMBOL_GPL(xas_split_alloc); + +/** + * xas_split() - Split a multi-index entry into smaller entries. + * @xas: XArray operation state. + * @entry: New entry to store in the array. + * @order: New entry order. + * + * The value in the entry is copied to all the replacement entries. + * + * Context: Any context. The caller should hold the xa_lock. + */ +void xas_split(struct xa_state *xas, void *entry, unsigned int order) +{ + unsigned int sibs = (1 << (order % XA_CHUNK_SHIFT)) - 1; + unsigned int offset, marks; + struct xa_node *node; + void *curr = xas_load(xas); + int values = 0; + + node = xas->xa_node; + if (xas_top(node)) + return; + + marks = node_get_marks(node, xas->xa_offset); + + offset = xas->xa_offset + sibs; + do { + if (xas->xa_shift < node->shift) { + struct xa_node *child = xas->xa_alloc; + + xas->xa_alloc = rcu_dereference_raw(child->parent); + child->shift = node->shift - XA_CHUNK_SHIFT; + child->offset = offset; + child->count = XA_CHUNK_SIZE; + child->nr_values = xa_is_value(entry) ? + XA_CHUNK_SIZE : 0; + RCU_INIT_POINTER(child->parent, node); + node_set_marks(node, offset, child, marks); + rcu_assign_pointer(node->slots[offset], + xa_mk_node(child)); + if (xa_is_value(curr)) + values--; + } else { + unsigned int canon = offset - xas->xa_sibs; + + node_set_marks(node, canon, NULL, marks); + rcu_assign_pointer(node->slots[canon], entry); + while (offset > canon) + rcu_assign_pointer(node->slots[offset--], + xa_mk_sibling(canon)); + values += (xa_is_value(entry) - xa_is_value(curr)) * + (xas->xa_sibs + 1); + } + } while (offset-- > xas->xa_offset); + + node->nr_values += values; +} +EXPORT_SYMBOL_GPL(xas_split); +#endif + /** * xas_pause() - Pause a walk to drop a lock. * @xas: XArray operation state. @@ -1407,7 +1557,7 @@ EXPORT_SYMBOL(__xa_store); * @gfp: Memory allocation flags. * * After this function returns, loads from this index will return @entry. - * Storing into an existing multislot entry updates the entry of every index. + * Storing into an existing multi-index entry updates the entry of every index. * The marks associated with @index are unaffected unless @entry is %NULL. * * Context: Any context. Takes and releases the xa_lock. @@ -1549,7 +1699,7 @@ static void xas_set_range(struct xa_state *xas, unsigned long first, * * After this function returns, loads from any index between @first and @last, * inclusive will return @entry. - * Storing into an existing multislot entry updates the entry of every index. + * Storing into an existing multi-index entry updates the entry of every index. * The marks associated with @index are unaffected unless @entry is %NULL. * * Context: Process context. Takes and releases the xa_lock. May sleep