[PATCH RFC] fs: erofs: support PG_mappedtodisk flag for folios with zero-filled

[Barry Song <21cnbao@gmail.com>]

From: Barry Song <v-songbaohua@oppo.com>

When a folio has never been zero-filled, mark it as mappedtodisk
to allow other software components to recognize and utilize the
flag.

Signed-off-by: Barry Song <v-songbaohua@oppo.com>
---
 fs/erofs/fileio.c | 2 ++
 fs/erofs/zdata.c  | 6 +++++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/erofs/fileio.c b/fs/erofs/fileio.c
index 3af96b1e2c2a..aa4cb438ea95 100644
--- a/fs/erofs/fileio.c
+++ b/fs/erofs/fileio.c
@@ -88,6 +88,7 @@ static int erofs_fileio_scan_folio(struct erofs_fileio *io, struct folio *folio)
 	struct erofs_map_blocks *map = &io->map;
 	unsigned int cur = 0, end = folio_size(folio), len, attached = 0;
 	loff_t pos = folio_pos(folio), ofs;
+	bool fully_mapped = true;
 	struct iov_iter iter;
 	struct bio_vec bv;
 	int err = 0;
@@ -124,6 +125,7 @@ static int erofs_fileio_scan_folio(struct erofs_fileio *io, struct folio *folio)
 			erofs_put_metabuf(&buf);
 		} else if (!(map->m_flags & EROFS_MAP_MAPPED)) {
 			folio_zero_segment(folio, cur, cur + len);
+			fully_mapped = false;
 			attached = 0;
 		} else {
 			if (io->rq && (map->m_pa + ofs != io->dev.m_pa ||
diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 8936790618c6..0158de4f3d95 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -926,7 +926,7 @@ static int z_erofs_scan_folio(struct z_erofs_decompress_frontend *f,
 	const loff_t offset = folio_pos(folio);
 	const unsigned int bs = i_blocksize(inode);
 	unsigned int end = folio_size(folio), split = 0, cur, pgs;
-	bool tight, excl;
+	bool tight, excl, fully_mapped = true;
 	int err = 0;
 
 	tight = (bs == PAGE_SIZE);
@@ -949,6 +949,7 @@ static int z_erofs_scan_folio(struct z_erofs_decompress_frontend *f,
 
 		if (!(map->m_flags & EROFS_MAP_MAPPED)) {
 			folio_zero_segment(folio, cur, end);
+			fully_mapped = false;
 			tight = false;
 		} else if (map->m_flags & EROFS_MAP_FRAGMENT) {
 			erofs_off_t fpos = offset + cur - map->m_la;
@@ -1009,6 +1010,9 @@ static int z_erofs_scan_folio(struct z_erofs_decompress_frontend *f,
 			tight = (bs == PAGE_SIZE);
 		}
 	} while ((end = cur) > 0);
+
+	if (fully_mapped)
+		folio_set_mappedtodisk(folio);
 	erofs_onlinefolio_end(folio, err);
 	return err;
 }
-- 
2.39.3 (Apple Git-146)