bcachefs: Switch darray to kvmalloc()

We sometimes use darrays for quite large buffers - the btree write
buffer in particular needs large buffers, since it must be sized to hold
all the write buffer keys outstanding in the journal.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/darray.c

@@ -9,10 +9,12 @@ int __bch2_darray_resize(darray_void *d, size_t element_size, size_t new_size, g
 	if (new_size > d->size) {
 		new_size = roundup_pow_of_two(new_size);
 
-		void *data = krealloc_array(d->data, new_size, element_size, gfp);
+		void *data = kvmalloc_array(new_size, element_size, gfp);
 		if (!data)
 			return -ENOMEM;
 
+		memcpy(data, d->data, d->size * element_size);
+		kvfree(d->data);
 		d->data	= data;
 		d->size = new_size;
 	}

fs/bcachefs/darray.h

@@ -92,7 +92,7 @@ do {									\
 
 #define darray_exit(_d)							\
 do {									\
-	kfree((_d)->data);						\
+	kvfree((_d)->data);						\
 	darray_init(_d);						\
 } while (0)