[PATCH 1/4] filemap: return pos of first dirty folio from range_has_writeback

Brian Foster
2024-07-18T13:01:32Z

The iomap layer has a use case that wants to locate the first dirty
or writeback folio in a particular range.
filemap_range_has_writeback() already implements this with the
exception that it only returns a boolean.

Since the _needs_writeback() wrapper is currently the only caller,
tweak has_writeback to take a pointer for the starting offset and
update it to the offset of the first dirty folio found.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---
include/linux/pagemap.h | 4 ++--
mm/filemap.c | 8 +++++---
2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index a0a026d2d244..a15131a3fa12 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -1217,7 +1217,7 @@ int __filemap_add_folio(struct address_space *mapping, struct folio *folio,
pgoff_t index, gfp_t gfp, void **shadowp);

bool filemap_range_has_writeback(struct address_space *mapping,
- loff_t start_byte, loff_t end_byte);
+ loff_t *start_byte, loff_t end_byte);

/**
* filemap_range_needs_writeback - check if range potentially needs writeback
@@ -1242,7 +1242,7 @@ static inline bool filemap_range_needs_writeback(struct address_space *mapping,
if (!mapping_tagged(mapping, PAGECACHE_TAG_DIRTY) &&
!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
return false;
- return filemap_range_has_writeback(mapping, start_byte, end_byte);
+ return filemap_range_has_writeback(mapping, &start_byte, end_byte);
}

/**
diff --git a/mm/filemap.c b/mm/filemap.c
index 657bcd887fdb..be0a219e8d9e 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -636,13 +636,13 @@ static bool mapping_needs_writeback(struct address_space *mapping)
}

bool filemap_range_has_writeback(struct address_space *mapping,
- loff_t start_byte, loff_t end_byte)
+ loff_t *start_byte, loff_t end_byte)
{
- XA_STATE(xas, &mapping->i_pages, start_byte >> PAGE_SHIFT);
+ XA_STATE(xas, &mapping->i_pages, *start_byte >> PAGE_SHIFT);
pgoff_t max = end_byte >> PAGE_SHIFT;
struct folio *folio;

- if (end_byte < start_byte)
+ if (end_byte < *start_byte)
return false;

rcu_read_lock();
@@ -655,6 +655,8 @@ bool filemap_range_has_writeback(struct address_space *mapping,
folio_test_writeback(folio))
break;
}
+ if (folio)
+ *start_byte = folio_pos(folio);
rcu_read_unlock();
return folio != NULL;
}
--
2.45.0