On 11 Feb 2025, at 10:50, Zi Yan wrote:
> It is 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 <ziy@xxxxxxxxxx>
> ---
> Documentation/core-api/xarray.rst | 14 ++-
> include/linux/xarray.h | 7 ++
> lib/test_xarray.c | 47 +++++++++++
> lib/xarray.c | 136 ++++++++++++++++++++++++++----
> tools/testing/radix-tree/Makefile | 1 +
> 5 files changed, 188 insertions(+), 17 deletions(-)
Hi Andrew,
Do you mind folding the diff below to this one? I changed the function
name but forgot the one in the xarray test. Thanks.
diff --git a/lib/test_xarray.c b/lib/test_xarray.c
index 598ca38a2f5b..cc2dd325158f 100644
--- a/lib/test_xarray.c
+++ b/lib/test_xarray.c
@@ -1868,7 +1868,7 @@ static void check_split_2(struct xarray *xa, unsigned long index,
xa_set_mark(xa, index, XA_MARK_1);
xas_lock(&xas);
- xas_try_halve(&xas, xa, order, GFP_KERNEL);
+ xas_try_split(&xas, xa, order, GFP_KERNEL);
if (((new_order / XA_CHUNK_SHIFT) < (order / XA_CHUNK_SHIFT)) &&
new_order < order - 1) {
XA_BUG_ON(xa, !xas_error(&xas) || xas_error(&xas) != -EINVAL);
Best Regards,
Yan, Zi
