[PATCH 2/7] mm: stop passing a writeback_control structure to shmem_writeout

Christoph Hellwig
2025-05-08T05:49:58Z

shmem_writeout only needs the swap_iocb cookie and the split folio
list. Pass those explicitly and remove the now unused list member
from struct writeback_control.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
drivers/gpu/drm/i915/gem/i915_gem_shmem.c | 2 +-
drivers/gpu/drm/ttm/ttm_backup.c | 9 +-------
include/linux/shmem_fs.h | 5 ++++-
include/linux/writeback.h | 3 ---
mm/shmem.c | 25 ++++++++++++++---------
mm/vmscan.c | 12 +++++------
6 files changed, 26 insertions(+), 30 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
index 5e784db9f315..dbb7a78ceea7 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
@@ -318,7 +318,7 @@ void __shmem_writeback(size_t size, struct address_space *mapping)
if (folio_mapped(folio))
folio_redirty_for_writepage(&wbc, folio);
else
- error = shmem_writeout(folio, &wbc);
+ error = shmem_writeout(folio, NULL, NULL);
}
}

diff --git a/drivers/gpu/drm/ttm/ttm_backup.c b/drivers/gpu/drm/ttm/ttm_backup.c
index ffaab68bd5dd..6f2e58be4f3e 100644
--- a/drivers/gpu/drm/ttm/ttm_backup.c
+++ b/drivers/gpu/drm/ttm/ttm_backup.c
@@ -112,15 +112,8 @@ ttm_backup_backup_page(struct file *backup, struct page *page,

if (writeback && !folio_mapped(to_folio) &&
folio_clear_dirty_for_io(to_folio)) {
- 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,
- };
folio_set_reclaim(to_folio);
- ret = shmem_writeout(to_folio, &wbc);
+ ret = shmem_writeout(to_folio, NULL, NULL);
if (!folio_test_writeback(to_folio))
folio_clear_reclaim(to_folio);
/*
diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index 5f03a39a26f7..6d0f9c599ff7 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -11,6 +11,8 @@
#include <linux/fs_parser.h>
#include <linux/userfaultfd_k.h>

+struct swap_iocb;
+
/* inode in-kernel data */

#ifdef CONFIG_TMPFS_QUOTA
@@ -107,7 +109,8 @@ static inline bool shmem_mapping(struct address_space *mapping)
void shmem_unlock_mapping(struct address_space *mapping);
struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
pgoff_t index, gfp_t gfp_mask);
-int shmem_writeout(struct folio *folio, struct writeback_control *wbc);
+int shmem_writeout(struct folio *folio, struct swap_iocb **plug,
+ struct list_head *folio_list);
void shmem_truncate_range(struct inode *inode, loff_t start, loff_t end);
int shmem_unuse(unsigned int type);

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index eda4b62511f7..82f217970092 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -79,9 +79,6 @@ struct writeback_control {
*/
struct swap_iocb **swap_plug;

- /* Target list for splitting a large folio */
- struct list_head *list;
-
/* internal fields used by the ->writepages implementation: */
struct folio_batch fbatch;
pgoff_t index;
diff --git a/mm/shmem.c b/mm/shmem.c
index 858cee02ca49..941b9b29e78a 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1540,10 +1540,13 @@ int shmem_unuse(unsigned int type)
* shmem_writeout - Write the folio to swap
* @folio: The folio to write
* @wbc: How writeback is to be done
+ * @plug: swap plug
+ * @folio_list: list to put back folios on split
*
* Move the folio from the page cache to the swap cache.
*/
-int shmem_writeout(struct folio *folio, struct writeback_control *wbc)
+int shmem_writeout(struct folio *folio, struct swap_iocb **plug,
+ struct list_head *folio_list)
{
struct address_space *mapping = folio->mapping;
struct inode *inode = mapping->host;
@@ -1553,9 +1556,6 @@ int shmem_writeout(struct folio *folio, struct writeback_control *wbc)
int nr_pages;
bool split = false;

- if (WARN_ON_ONCE(!wbc->for_reclaim))
- goto redirty;
-
if ((info->flags & VM_LOCKED) || sbinfo->noswap)
goto redirty;

@@ -1582,7 +1582,7 @@ int shmem_writeout(struct folio *folio, struct writeback_control *wbc)
try_split:
/* Ensure the subpages are still dirty */
folio_test_set_dirty(folio);
- if (split_folio_to_list(folio, wbc->list))
+ if (split_folio_to_list(folio, folio_list))
goto redirty;
folio_clear_dirty(folio);
}
@@ -1635,13 +1635,21 @@ int shmem_writeout(struct folio *folio, struct writeback_control *wbc)
list_add(&info->swaplist, &shmem_swaplist);

if (!folio_alloc_swap(folio, __GFP_HIGH | __GFP_NOMEMALLOC | __GFP_NOWARN)) {
+ 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,
+ };
shmem_recalc_inode(inode, 0, nr_pages);
swap_shmem_alloc(folio->swap, nr_pages);
shmem_delete_from_page_cache(folio, swp_to_radix_entry(folio->swap));

mutex_unlock(&shmem_swaplist_mutex);
BUG_ON(folio_mapped(folio));
- return swap_writeout(folio, wbc);
+ return swap_writeout(folio, &wbc);
}

list_del_init(&info->swaplist);
@@ -1650,10 +1658,7 @@ int shmem_writeout(struct folio *folio, struct writeback_control *wbc)
goto try_split;
redirty:
folio_mark_dirty(folio);
- if (wbc->for_reclaim)
- return AOP_WRITEPAGE_ACTIVATE; /* Return with folio locked */
- folio_unlock(folio);
- return 0;
+ return AOP_WRITEPAGE_ACTIVATE; /* Return with folio locked */
}
EXPORT_SYMBOL_GPL(shmem_writeout);

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 42302d2b8739..fea78f01d04e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -669,15 +669,13 @@ static pageout_t writeout(struct folio *folio, struct address_space *mapping,

/*
* The large shmem folio can be split if CONFIG_THP_SWAP is not enabled
- * or we failed to allocate contiguous swap entries.
+ * or we failed to allocate contiguous swap entries, in which case
+ * the split out folios get added back to folio_list.
*/
- if (shmem_mapping(mapping)) {
- if (folio_test_large(folio))
- wbc.list = folio_list;
- res = shmem_writeout(folio, &wbc);
- } else {
+ if (shmem_mapping(mapping))
+ res = shmem_writeout(folio, plug, folio_list);
+ else
res = swap_writeout(folio, &wbc);
- }

if (res < 0)
handle_write_error(mapping, folio, res);
--
2.47.2