[RFC PATCH net-next 04/12] io_uring/opaque: add owned-page helpers for dense copies

[Alex Markuze]

Add the accounted destination-page allocator used by CREATE and compaction.
Prefer compound allocations up to 64 KiB, or one base page when larger,
and fall back to smaller orders.

Signed-off-by: Alex Markuze <amarkuze@xxxxxxxxxx>
---
 io_uring/Makefile         |  2 +-
 io_uring/opaque_compact.c | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 io_uring/opaque_compact.c

diff --git a/io_uring/Makefile b/io_uring/Makefile
index 81710127046c..191316972e04 100644
--- a/io_uring/Makefile
+++ b/io_uring/Makefile
@@ -17,7 +17,7 @@ obj-$(CONFIG_IO_URING)		+= io_uring.o opdef.o kbuf.o rsrc.o notif.o \
 					query.o loop.o
 
 obj-$(CONFIG_IO_URING_ZCRX)	+= zcrx.o
-obj-$(CONFIG_IO_URING_OPAQUE_OBJ)	+= opaque.o
+obj-$(CONFIG_IO_URING_OPAQUE_OBJ)	+= opaque.o opaque_compact.o
 obj-$(CONFIG_IO_WQ)		+= io-wq.o
 obj-$(CONFIG_FUTEX)		+= futex.o
 obj-$(CONFIG_EPOLL)		+= epoll.o
diff --git a/io_uring/opaque_compact.c b/io_uring/opaque_compact.c
new file mode 100644
index 000000000000..b59c7cb95d42
--- /dev/null
+++ b/io_uring/opaque_compact.c
@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Workers copy immutable backing without holding object table locks. */
+#include <linux/highmem.h>
+#include <linux/memcontrol.h>
+#include <linux/mm.h>
+#include <linux/overflow.h>
+#include <linux/sched.h>
+#include <linux/sizes.h>
+#include <linux/slab.h>
+
+#include "io_uring.h"
+#include "opaque_internal.h"
+
+struct page *io_opaque_owned_page(unsigned int *order)
+{
+	struct page *page;
+
+	for (;;) {
+		page = alloc_pages(GFP_KERNEL_ACCOUNT | __GFP_COMP | __GFP_NORETRY |
+				   __GFP_NOWARN, *order);
+		if (page || !*order)
+			return page;
+		(*order)--;
+	}
+}
+
+/* Destination allocation for dense copies and CREATE. */
+struct page *io_opaque_dest_page(struct io_opaque_store *store, u64 pages_left,
+				 unsigned int *order)
+{
+	*order = min_t(unsigned int, IO_OPAQUE_MAX_ORDER, ilog2(pages_left));
+	return io_opaque_owned_page(order);
+}
-- 
2.34.1