f2fs: introduce a new direct_IO write path

Previously, f2fs doesn't support direct IOs with high performance, which throws
every write requests via the buffered write path, resulting in highly
performance degradation due to memory opeations like copy_from_user.

This patch introduces a new direct IO path in which every write requests are
processed by generic blockdev_direct_IO() with enhanced get_block function.

The get_data_block() in f2fs handles:
1. if original data blocks are allocates, then give them to blockdev.
2. otherwise,
  a. preallocate requested block addresses
  b. do not use extent cache for better performance
  c. give the block addresses to blockdev

This policy induces that:
- new allocated data are sequentially written to the disk
- updated data are randomly written to the disk.
- f2fs gives consistency on its file meta, not file data.

Reviewed-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

1 files changed, 15 insertions, 8 deletions

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 5b890ce74b15..9f8bdd02e3a8 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -854,16 +854,14 @@ static int __get_segment_type(struct page *page, enum page_type p_type)
         return __get_segment_type_6(page, p_type);
 }
 
-static void do_write_page(struct f2fs_sb_info *sbi, struct page *page,
-                        block_t old_blkaddr, block_t *new_blkaddr,
-                        struct f2fs_summary *sum, struct f2fs_io_info *fio)
+void allocate_data_block(struct f2fs_sb_info *sbi, struct page *page,
+                block_t old_blkaddr, block_t *new_blkaddr,
+                struct f2fs_summary *sum, int type)
 {
         struct sit_info *sit_i = SIT_I(sbi);
         struct curseg_info *curseg;
         unsigned int old_cursegno;
-        int type;
 
-        type = __get_segment_type(page, fio->type);
         curseg = CURSEG_I(sbi, type);
 
         mutex_lock(&curseg->curseg_mutex);
@@ -896,13 +894,22 @@ static void do_write_page(struct f2fs_sb_info *sbi, struct page *page,
         locate_dirty_segment(sbi, GET_SEGNO(sbi, old_blkaddr));
         mutex_unlock(&sit_i->sentry_lock);
 
-        if (fio->type == NODE)
+        if (page && IS_NODESEG(type))
                 fill_node_footer_blkaddr(page, NEXT_FREE_BLKADDR(sbi, curseg));
 
+        mutex_unlock(&curseg->curseg_mutex);
+}
+
+static void do_write_page(struct f2fs_sb_info *sbi, struct page *page,
+                        block_t old_blkaddr, block_t *new_blkaddr,
+                        struct f2fs_summary *sum, struct f2fs_io_info *fio)
+{
+        int type = __get_segment_type(page, fio->type);
+
+        allocate_data_block(sbi, page, old_blkaddr, new_blkaddr, sum, type);
+
         /* writeout dirty page into bdev */
         f2fs_submit_page_mbio(sbi, page, *new_blkaddr, fio);
-
-        mutex_unlock(&curseg->curseg_mutex);
 }
 
 void write_meta_page(struct f2fs_sb_info *sbi, struct page *page)