[RFC PATCH 3/9] shmem: move folio zero operation to write_begin()

Daniel Gomez
2024-02-09T14:29:15Z

Simplify zero out operation by moving it from write_end() to the
write_begin(). If a large folio does not have any block uptodate when we
first get it, zero it out entirely.

Signed-off-by: Daniel Gomez <da.gomez@samsung.com>
---
mm/shmem.c | 27 ++++++++++++++++++++-------
1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 5980d7b94f65..3bddf7a89c18 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -149,6 +149,14 @@ static inline bool sfs_is_fully_uptodate(struct folio *folio)
return bitmap_full(sfs->state, i_blocks_per_folio(inode, folio));
}

+static inline bool sfs_is_any_uptodate(struct folio *folio)
+{
+ struct inode *inode = folio->mapping->host;
+ struct shmem_folio_state *sfs = folio->private;
+
+ return !bitmap_empty(sfs->state, i_blocks_per_folio(inode, folio));
+}
+
static inline bool sfs_is_block_uptodate(struct shmem_folio_state *sfs,
unsigned int block)
{
@@ -239,6 +247,15 @@ static void sfs_free(struct folio *folio, bool force)
kfree(folio_detach_private(folio));
}

+static inline bool shmem_is_any_uptodate(struct folio *folio)
+{
+ struct shmem_folio_state *sfs = folio->private;
+
+ if (folio_test_large(folio) && sfs)
+ return sfs_is_any_uptodate(folio);
+ return folio_test_uptodate(folio);
+}
+
static void shmem_set_range_uptodate(struct folio *folio, size_t off,
size_t len)
{
@@ -2845,6 +2862,9 @@ shmem_write_begin(struct file *file, struct address_space *mapping,
if (ret)
return ret;

+ if (!shmem_is_any_uptodate(folio))
+ folio_zero_range(folio, 0, folio_size(folio));
+
*pagep = folio_file_page(folio, index);
if (PageHWPoison(*pagep)) {
folio_unlock(folio);
@@ -2867,13 +2887,6 @@ shmem_write_end(struct file *file, struct address_space *mapping,
if (pos + copied > inode->i_size)
i_size_write(inode, pos + copied);

- if (!folio_test_uptodate(folio)) {
- if (copied < folio_size(folio)) {
- size_t from = offset_in_folio(folio, pos);
- folio_zero_segments(folio, 0, from,
- from + copied, folio_size(folio));
- }
- }
shmem_set_range_uptodate(folio, 0, folio_size(folio));
folio_mark_dirty(folio);
folio_unlock(folio);
--
2.43.0