Hi Zi, On 2025/2/19 07:50, Zi Yan wrote:
A preparation patch for non-uniform folio split, which always split a folio into half iteratively, and minimal xarray entry split.Currently, xas_split_alloc() and xas_split() always split all slots from a multi-index entry. They cost the same number of xa_node as the to-be-split slots. For example, to split an order-9 entry, which takes 2^(9-6)=8 slots, assuming XA_CHUNK_SHIFT is 6 (!CONFIG_BASE_SMALL), 8 xa_node are needed. Instead xas_try_split() is intended to be used iteratively to split the order-9 entry into 2 order-8 entries, then split one order-8 entry, based on the given index, to 2 order-7 entries, ..., and split one order-1 entry to 2 order-0 entries. When splitting the order-6 entry and a new xa_node is needed, xas_try_split() will try to allocate one if possible. As a result, xas_try_split() would only need one xa_node instead of 8. When a new xa_node is needed during the split, xas_try_split() can try to allocate one but no more. -ENOMEM will be return if a node cannot be allocated. -EINVAL will be return if a sibling node is split or cascade split happens, where two or more new nodes are needed, and these are not supported by xas_try_split(). xas_split_alloc() and xas_split() split an order-9 to order-0: --------------------------------- | | | | | | | | | | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | | | | | | | | | | --------------------------------- | | | | ------- --- --- ------- | | ... | | V V V V ----------- ----------- ----------- ----------- | xa_node | | xa_node | ... | xa_node | | xa_node | ----------- ----------- ----------- ----------- xas_try_split() splits an order-9 to order-0: --------------------------------- | | | | | | | | | | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | | | | | | | | | | --------------------------------- | | V ----------- | xa_node | ----------- Signed-off-by: Zi Yan <[email protected]> Cc: Baolin Wang <[email protected]> Cc: David Hildenbrand <[email protected]> Cc: Hugh Dickins <[email protected]> Cc: John Hubbard <[email protected]> Cc: Kefeng Wang <[email protected]> Cc: Kirill A. Shuemov <[email protected]> Cc: Miaohe Lin <[email protected]> Cc: Matthew Wilcox <[email protected]> Cc: Ryan Roberts <[email protected]> Cc: Yang Shi <[email protected]> Cc: Yu Zhao <[email protected]> Cc: Zi Yan <[email protected]> --- Documentation/core-api/xarray.rst | 14 ++- include/linux/xarray.h | 7 ++ lib/test_xarray.c | 47 ++++++++++ lib/xarray.c | 138 ++++++++++++++++++++++++++---- tools/testing/radix-tree/Makefile | 1 + 5 files changed, 190 insertions(+), 17 deletions(-) diff --git a/Documentation/core-api/xarray.rst b/Documentation/core-api/xarray.rst index f6a3eef4fe7f..c6c91cbd0c3c 100644 --- a/Documentation/core-api/xarray.rst +++ b/Documentation/core-api/xarray.rst @@ -489,7 +489,19 @@ 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(). +and calling xas_split() or calling xas_try_split() with xa_lock. The +difference between xas_split_alloc()+xas_split() and xas_try_alloc() is +that xas_split_alloc() + xas_split() split the entry from the original +order to the new order in one shot uniformly, whereas xas_try_split() +iteratively splits the entry containing the index non-uniformly. +For example, to split an order-9 entry, which takes 2^(9-6)=8 slots, +assuming ``XA_CHUNK_SHIFT`` is 6, xas_split_alloc() + xas_split() need +8 xa_node. xas_try_split() splits the order-9 entry into +2 order-8 entries, then split one order-8 entry, based on the given index, +to 2 order-7 entries, ..., and split one order-1 entry to 2 order-0 entries. +When splitting the order-6 entry and a new xa_node is needed, xas_try_split() +will try to allocate one if possible. As a result, xas_try_split() would only +need 1 xa_node instead of 8.Functions and structures======================== diff --git a/include/linux/xarray.h b/include/linux/xarray.h index 0b618ec04115..9eb8c7425090 100644 --- a/include/linux/xarray.h +++ b/include/linux/xarray.h @@ -1555,6 +1555,8 @@ int xa_get_order(struct xarray *, unsigned long index); int xas_get_order(struct xa_state *xas); 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); +void xas_try_split(struct xa_state *xas, void *entry, unsigned int order, + gfp_t gfp); #else static inline int xa_get_order(struct xarray *xa, unsigned long index) { @@ -1576,6 +1578,11 @@ static inline void xas_split_alloc(struct xa_state *xas, void *entry, unsigned int order, gfp_t gfp) { } + +static inline void xas_try_split(struct xa_state *xas, void *entry, + unsigned int order, gfp_t gfp) +{ +} #endif/**
[snip]
diff --git a/lib/xarray.c b/lib/xarray.c index 116e9286c64e..b9a63d7fbd58 100644 --- a/lib/xarray.c +++ b/lib/xarray.c @@ -1007,6 +1007,31 @@ static void node_set_marks(struct xa_node *node, unsigned int offset, } }+static struct xa_node *__xas_alloc_node_for_split(struct xa_state *xas,+ void *entry, gfp_t gfp) +{ + unsigned int i; + void *sibling = NULL; + struct xa_node *node; + unsigned int mask = xas->xa_sibs; + + node = kmem_cache_alloc_lru(radix_tree_node_cachep, xas->xa_lru, gfp); + if (!node) + return NULL; + 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(i); + } else { + RCU_INIT_POINTER(node->slots[i], sibling); + } + } + RCU_INIT_POINTER(node->parent, xas->xa_alloc); + + return node; +} + /** * xas_split_alloc() - Allocate memory for splitting an entry. * @xas: XArray operation state. @@ -1025,7 +1050,6 @@ 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)) @@ -1034,23 +1058,9 @@ void xas_split_alloc(struct xa_state *xas, void *entry, unsigned int order, return;do {- unsigned int i; - void *sibling = NULL; - struct xa_node *node; - - node = kmem_cache_alloc_lru(radix_tree_node_cachep, xas->xa_lru, gfp); + struct xa_node *node = __xas_alloc_node_for_split(xas, entry, 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(i); - } else { - RCU_INIT_POINTER(node->slots[i], sibling); - } - } - RCU_INIT_POINTER(node->parent, xas->xa_alloc); xas->xa_alloc = node; } while (sibs-- > 0);@@ -1122,6 +1132,102 @@ void xas_split(struct xa_state *xas, void *entry, unsigned int order)xas_update(xas, node); } EXPORT_SYMBOL_GPL(xas_split); + +/** + * xas_try_split() - Try to split a multi-index entry. + * @xas: XArray operation state. + * @entry: New entry to store in the array. + * @order: Current entry order. + * @gfp: Memory allocation flags. + * + * The size of the new entries is set in @xas. The value in @entry is + * copied to all the replacement entries. If and only if one xa_node needs to + * be allocated, the function will use @gfp to get one. If more xa_node are + * needed, the function gives EINVAL error. + * + * Context: Any context. The caller should hold the xa_lock. + */ +void xas_try_split(struct xa_state *xas, void *entry, unsigned int order, + gfp_t gfp)
The xas_try_split() may sleep if ‘gfp’ flags permit while holding the xa_lock, which can cause issues. So can we add a check for the ‘gfp’ or only use GFP_NOWAIT?
