This patch switches swap-out to SWP_FS_OPS swap-spaces to use ->swap_rw
and makes the writes asynchronous, like they are for other swap spaces.
To make it async we need to allocate the kiocb struct from a mempool.
This may block, but won't block as long as waiting for the write to
complete. At most it will wait for some previous swap IO to complete.
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: NeilBrown <neilb@xxxxxxx>
---
mm/page_io.c | 98 ++++++++++++++++++++++++++++++++++------------------------
1 file changed, 58 insertions(+), 40 deletions(-)
diff --git a/mm/page_io.c b/mm/page_io.c
index 52d423c9962b..a01cc273bb00 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -303,6 +303,57 @@ int sio_pool_init(void)
return 0;
}
+static void sio_write_complete(struct kiocb *iocb, long ret)
+{
+ struct swap_iocb *sio = container_of(iocb, struct swap_iocb, iocb);
+ struct page *page = sio->bvec.bv_page;
+
+ if (ret != PAGE_SIZE) {
+ /*
+ * In the case of swap-over-nfs, this can be a
+ * temporary failure if the system has limited
+ * memory for allocating transmit buffers.
+ * Mark the page dirty and avoid
+ * folio_rotate_reclaimable but rate-limit the
+ * messages but do not flag PageError like
+ * the normal direct-to-bio case as it could
+ * be temporary.
+ */
+ set_page_dirty(page);
+ ClearPageReclaim(page);
+ pr_err_ratelimited("Write error %ld on dio swapfile (%llu)\n",
+ ret, page_file_offset(page));
+ } else
+ count_vm_event(PSWPOUT);
+ end_page_writeback(page);
+ mempool_free(sio, sio_pool);
+}
+
+static int swap_writepage_fs(struct page *page, struct writeback_control *wbc)
+{
+ struct swap_iocb *sio;
+ struct swap_info_struct *sis = page_swap_info(page);
+ struct file *swap_file = sis->swap_file;
+ struct address_space *mapping = swap_file->f_mapping;
+ struct iov_iter from;
+ int ret;
+
+ set_page_writeback(page);
+ unlock_page(page);
+ sio = mempool_alloc(sio_pool, GFP_NOIO);
+ init_sync_kiocb(&sio->iocb, swap_file);
+ sio->iocb.ki_complete = sio_write_complete;
+ sio->iocb.ki_pos = page_file_offset(page);
+ sio->bvec.bv_page = page;
+ sio->bvec.bv_len = PAGE_SIZE;
+ sio->bvec.bv_offset = 0;
+ iov_iter_bvec(&from, WRITE, &sio->bvec, 1, PAGE_SIZE);
+ ret = mapping->a_ops->swap_rw(&sio->iocb, &from);
+ if (ret != -EIOCBQUEUED)
+ sio_write_complete(&sio->iocb, ret);
+ return ret;
+}
+
int __swap_writepage(struct page *page, struct writeback_control *wbc,
bio_end_io_t end_write_func)
{
@@ -311,46 +362,13 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
struct swap_info_struct *sis = page_swap_info(page);
VM_BUG_ON_PAGE(!PageSwapCache(page), page);
- if (data_race(sis->flags & SWP_FS_OPS)) {
- struct kiocb kiocb;
- struct file *swap_file = sis->swap_file;
- struct address_space *mapping = swap_file->f_mapping;
- struct bio_vec bv = {
- .bv_page = page,
- .bv_len = PAGE_SIZE,
- .bv_offset = 0
- };
- struct iov_iter from;
-
- iov_iter_bvec(&from, WRITE, &bv, 1, PAGE_SIZE);
- init_sync_kiocb(&kiocb, swap_file);
- kiocb.ki_pos = page_file_offset(page);
-
- set_page_writeback(page);
- unlock_page(page);
- ret = mapping->a_ops->direct_IO(&kiocb, &from);
- if (ret == PAGE_SIZE) {
- count_vm_event(PSWPOUT);
- ret = 0;
- } else {
- /*
- * In the case of swap-over-nfs, this can be a
- * temporary failure if the system has limited
- * memory for allocating transmit buffers.
- * Mark the page dirty and avoid
- * folio_rotate_reclaimable but rate-limit the
- * messages but do not flag PageError like
- * the normal direct-to-bio case as it could
- * be temporary.
- */
- set_page_dirty(page);
- ClearPageReclaim(page);
- pr_err_ratelimited("Write error on dio swapfile (%llu)\n",
- page_file_offset(page));
- }
- end_page_writeback(page);
- return ret;
- }
+ /*
+ * ->flags can be updated non-atomicially (scan_swap_map_slots),
+ * but that will never affect SWP_FS_OPS, so the data_race
+ * is safe.
+ */
+ if (data_race(sis->flags & SWP_FS_OPS))
+ return swap_writepage_fs(page, wbc);
ret = bdev_write_page(sis->bdev, swap_page_sector(page), page, wbc);
if (!ret) {
