[PATCH v13 088/137] mm/filemap: Add FGP_STABLE

Matthew Wilcox (Oracle)
2021-07-12T03:54:41Z

Allow filemap_get_folio() to wait for writeback to complete (if the
filesystem wants that behaviour). This is the folio equivalent of
grab_cache_page_write_begin(), which is moved into the folio-compat
file as a reminder to migrate all the code using it. This paves the
way for getting rid of AOP_FLAG_NOFS once grab_cache_page_write_begin()
is removed.

Kernel grows by 11 bytes. filemap_get_folio() grows by 33 bytes but
grab_cache_page_write_begin() shrinks by 22 bytes to make up for it.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
include/linux/pagemap.h | 1 +
mm/filemap.c | 25 +++----------------------
mm/folio-compat.c | 13 +++++++++++++
3 files changed, 17 insertions(+), 22 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 5183e371e80f..a9243fa697e8 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -301,6 +301,7 @@ pgoff_t page_cache_prev_miss(struct address_space *mapping,
#define FGP_FOR_MMAP 0x00000040
#define FGP_HEAD 0x00000080
#define FGP_ENTRY 0x00000100
+#define FGP_STABLE 0x00000200

struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
int fgp_flags, gfp_t gfp);
diff --git a/mm/filemap.c b/mm/filemap.c
index 3487153c2630..a918599fc851 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1817,6 +1817,7 @@ static void *mapping_get_entry(struct address_space *mapping, pgoff_t index)
* * %FGP_WRITE - The page will be written to by the caller.
* * %FGP_NOFS - __GFP_FS will get cleared in gfp.
* * %FGP_NOWAIT - Don't get blocked by page lock.
+ * * %FGP_STABLE - Wait for the folio to be stable (finished writeback)
*
* If %FGP_LOCK or %FGP_CREAT are specified then the function may sleep even
* if the %GFP flags specified for %FGP_CREAT are atomic.
@@ -1867,6 +1868,8 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
folio_clear_idle_flag(folio);
}

+ if (fgp_flags & FGP_STABLE)
+ folio_wait_stable(folio);
no_page:
if (!folio && (fgp_flags & FGP_CREAT)) {
int err;
@@ -3590,28 +3593,6 @@ generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from)
}
EXPORT_SYMBOL(generic_file_direct_write);

-/*
- * Find or create a page at the given pagecache position. Return the locked
- * page. This function is specifically for buffered writes.
- */
-struct page *grab_cache_page_write_begin(struct address_space *mapping,
- pgoff_t index, unsigned flags)
-{
- struct page *page;
- int fgp_flags = FGP_LOCK|FGP_WRITE|FGP_CREAT;
-
- if (flags & AOP_FLAG_NOFS)
- fgp_flags |= FGP_NOFS;
-
- page = pagecache_get_page(mapping, index, fgp_flags,
- mapping_gfp_mask(mapping));
- if (page)
- wait_for_stable_page(page);
-
- return page;
-}
-EXPORT_SYMBOL(grab_cache_page_write_begin);
-
ssize_t generic_perform_write(struct file *file,
struct iov_iter *i, loff_t pos)
{
diff --git a/mm/folio-compat.c b/mm/folio-compat.c
index e833e680e944..5b6ae1da314e 100644
--- a/mm/folio-compat.c
+++ b/mm/folio-compat.c
@@ -116,6 +116,7 @@ int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
}
EXPORT_SYMBOL(add_to_page_cache_lru);

+noinline
struct page *pagecache_get_page(struct address_space *mapping, pgoff_t index,
int fgp_flags, gfp_t gfp)
{
@@ -127,3 +128,15 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t index,
return folio_file_page(folio, index);
}
EXPORT_SYMBOL(pagecache_get_page);
+
+struct page *grab_cache_page_write_begin(struct address_space *mapping,
+ pgoff_t index, unsigned flags)
+{
+ unsigned fgp_flags = FGP_LOCK | FGP_WRITE | FGP_CREAT | FGP_STABLE;
+
+ if (flags & AOP_FLAG_NOFS)
+ fgp_flags |= FGP_NOFS;
+ return pagecache_get_page(mapping, index, fgp_flags,
+ mapping_gfp_mask(mapping));
+}
+EXPORT_SYMBOL(grab_cache_page_write_begin);
--
2.30.2