xarray: honor XA_FLAGS_ACCOUNT in xas_split_alloc()

XArray operations that allocate xa_nodes, such as xas_nomem() and
xas_alloc(), add __GFP_ACCOUNT when the array has XA_FLAGS_ACCOUNT set. 
This charges the allocated memory and avoids the workingset convergence
issue described by commit 7b785645e8 ("mm: fix page cache convergence
regression").

xas_split_alloc() does not add _GFP_ACCOUNT when XA_FLAGS_ACCOUNT is
present.  Fix it.

Link: https://lore.kernel.org/20260804-add-gfp_account-to-xas_split_alloc-v3-2-38cb3ff325c5@nvidia.com
Fixes: 6b24ca4a1a ("mm: Use multi-index entries in the page cache")
Signed-off-by: Zi Yan <[email protected]>
Reviewed-by: Lorenzo Stoakes (ARM) <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Cc: Baolin Wang <[email protected]>
Cc: Barry Song <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Dev Jain <[email protected]>
Cc: Lance Yang <[email protected]>
Cc: Liam R. Howlett <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: William Kucharski <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

lib/xarray.c

@@ -1053,6 +1053,9 @@ void xas_split_alloc(struct xa_state *xas, void *entry, unsigned int order,
 	if (xas->xa_shift + XA_CHUNK_SHIFT > order)
 		return;
 
+	if (xas->xa->xa_flags & XA_FLAGS_ACCOUNT)
+		gfp |= __GFP_ACCOUNT;
+
 	do {
 		struct xa_node *node;