[PATCH 1/7] mm: split out a writeout helper from pageout

Christoph Hellwig
2025-05-08T05:49:56Z

Move the code to write back swap / shmem folios into a self-contained
helper to keep prepare for refactoring it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
mm/vmscan.c | 94 +++++++++++++++++++++++++++--------------------------
1 file changed, 48 insertions(+), 46 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index c9f22abf0d38..42302d2b8739 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -652,14 +652,55 @@ typedef enum {
PAGE_CLEAN,
} pageout_t;

+static pageout_t writeout(struct folio *folio, struct address_space *mapping,
+ struct swap_iocb **plug, struct list_head *folio_list)
+{
+ struct writeback_control wbc = {
+ .sync_mode = WB_SYNC_NONE,
+ .nr_to_write = SWAP_CLUSTER_MAX,
+ .range_start = 0,
+ .range_end = LLONG_MAX,
+ .for_reclaim = 1,
+ .swap_plug = plug,
+ };
+ int res;
+
+ folio_set_reclaim(folio);
+
+ /*
+ * The large shmem folio can be split if CONFIG_THP_SWAP is not enabled
+ * or we failed to allocate contiguous swap entries.
+ */
+ if (shmem_mapping(mapping)) {
+ if (folio_test_large(folio))
+ wbc.list = folio_list;
+ res = shmem_writeout(folio, &wbc);
+ } else {
+ res = swap_writeout(folio, &wbc);
+ }
+
+ if (res < 0)
+ handle_write_error(mapping, folio, res);
+ if (res == AOP_WRITEPAGE_ACTIVATE) {
+ folio_clear_reclaim(folio);
+ return PAGE_ACTIVATE;
+ }
+
+ /* synchronous write? */
+ if (!folio_test_writeback(folio))
+ folio_clear_reclaim(folio);
+
+ trace_mm_vmscan_write_folio(folio);
+ node_stat_add_folio(folio, NR_VMSCAN_WRITE);
+ return PAGE_SUCCESS;
+}
+
/*
* pageout is called by shrink_folio_list() for each dirty folio.
*/
static pageout_t pageout(struct folio *folio, struct address_space *mapping,
struct swap_iocb **plug, struct list_head *folio_list)
{
- int (*writeout)(struct folio *, struct writeback_control *);
-
/*
* We no longer attempt to writeback filesystem folios here, other
* than tmpfs/shmem. That's taken care of in page-writeback.
@@ -690,51 +731,12 @@ static pageout_t pageout(struct folio *folio, struct address_space *mapping,
}
return PAGE_KEEP;
}
- if (shmem_mapping(mapping))
- writeout = shmem_writeout;
- else if (folio_test_anon(folio))
- writeout = swap_writeout;
- else
- return PAGE_ACTIVATE;
-
- if (folio_clear_dirty_for_io(folio)) {
- int res;
- struct writeback_control wbc = {
- .sync_mode = WB_SYNC_NONE,
- .nr_to_write = SWAP_CLUSTER_MAX,
- .range_start = 0,
- .range_end = LLONG_MAX,
- .for_reclaim = 1,
- .swap_plug = plug,
- };

- /*
- * The large shmem folio can be split if CONFIG_THP_SWAP is
- * not enabled or contiguous swap entries are failed to
- * allocate.
- */
- if (shmem_mapping(mapping) && folio_test_large(folio))
- wbc.list = folio_list;
-
- folio_set_reclaim(folio);
- res = writeout(folio, &wbc);
- if (res < 0)
- handle_write_error(mapping, folio, res);
- if (res == AOP_WRITEPAGE_ACTIVATE) {
- folio_clear_reclaim(folio);
- return PAGE_ACTIVATE;
- }
-
- if (!folio_test_writeback(folio)) {
- /* synchronous write? */
- folio_clear_reclaim(folio);
- }
- trace_mm_vmscan_write_folio(folio);
- node_stat_add_folio(folio, NR_VMSCAN_WRITE);
- return PAGE_SUCCESS;
- }
-
- return PAGE_CLEAN;
+ if (!shmem_mapping(mapping) && !folio_test_anon(folio))
+ return PAGE_ACTIVATE;
+ if (!folio_clear_dirty_for_io(folio))
+ return PAGE_CLEAN;
+ return writeout(folio, mapping, plug, folio_list);
}

/*
--
2.47.2