f2fs: give a chance to merge IOs by IO scheduler

Previously, background GC submits many 4KB read requests to load victim blocks
and/or its (i)node blocks.

...
f2fs_gc : f2fs_readpage: ino = 1, page_index = 0xb61, blkaddr = 0x3b964ed
f2fs_gc : block_rq_complete: 8,16 R () 499854968 + 8 [0]
f2fs_gc : f2fs_readpage: ino = 1, page_index = 0xb6f, blkaddr = 0x3b964ee
f2fs_gc : block_rq_complete: 8,16 R () 499854976 + 8 [0]
f2fs_gc : f2fs_readpage: ino = 1, page_index = 0xb79, blkaddr = 0x3b964ef
f2fs_gc : block_rq_complete: 8,16 R () 499854984 + 8 [0]
...

However, by the fact that many IOs are sequential, we can give a chance to merge
the IOs by IO scheduler.
In order to do that, let's use blk_plug.

...
f2fs_gc : f2fs_iget: ino = 143
f2fs_gc : f2fs_readpage: ino = 143, page_index = 0x1c6, blkaddr = 0x2e6ee
f2fs_gc : f2fs_iget: ino = 143
f2fs_gc : f2fs_readpage: ino = 143, page_index = 0x1c7, blkaddr = 0x2e6ef
<idle> : block_rq_complete: 8,16 R () 1519616 + 8 [0]
<idle> : block_rq_complete: 8,16 R () 1519848 + 8 [0]
<idle> : block_rq_complete: 8,16 R () 1520432 + 96 [0]
<idle> : block_rq_complete: 8,16 R () 1520536 + 104 [0]
<idle> : block_rq_complete: 8,16 R () 1521008 + 112 [0]
<idle> : block_rq_complete: 8,16 R () 1521440 + 152 [0]
<idle> : block_rq_complete: 8,16 R () 1521688 + 144 [0]
<idle> : block_rq_complete: 8,16 R () 1522128 + 192 [0]
<idle> : block_rq_complete: 8,16 R () 1523256 + 328 [0]
...

Note that this issue should be addressed in checkpoint, and some readahead
flows too.

Reviewed-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index 5a825502b0b0..a0aa0446a237 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -89,10 +89,13 @@ static void ra_nat_pages(struct f2fs_sb_info *sbi, int nid)
 {
         struct address_space *mapping = sbi->meta_inode->i_mapping;
         struct f2fs_nm_info *nm_i = NM_I(sbi);
+        struct blk_plug plug;
         struct page *page;
         pgoff_t index;
         int i;
 
+        blk_start_plug(&plug);
+
         for (i = 0; i < FREE_NID_PAGES; i++, nid += NAT_ENTRY_PER_BLOCK) {
                 if (nid >= nm_i->max_nid)
                         nid = 0;
@@ -110,6 +113,7 @@ static void ra_nat_pages(struct f2fs_sb_info *sbi, int nid)
 
                 f2fs_put_page(page, 0);
         }
+        blk_finish_plug(&plug);
 }
 
 static struct nat_entry *__lookup_nat_cache(struct f2fs_nm_info *nm_i, nid_t n)
@@ -942,6 +946,7 @@ struct page *get_node_page_ra(struct page *parent, int start)
 {
         struct f2fs_sb_info *sbi = F2FS_SB(parent->mapping->host->i_sb);
         struct address_space *mapping = sbi->node_inode->i_mapping;
+        struct blk_plug plug;
         struct page *page;
         int err, i, end;
         nid_t nid;
@@ -961,6 +966,8 @@ struct page *get_node_page_ra(struct page *parent, int start)
         else if (err == LOCKED_PAGE)
                 goto page_hit;
 
+        blk_start_plug(&plug);
+
         /* Then, try readahead for siblings of the desired node */
         end = start + MAX_RA_NODE;
         end = min(end, NIDS_PER_BLOCK);
@@ -971,6 +978,8 @@ struct page *get_node_page_ra(struct page *parent, int start)
                 ra_node_page(sbi, nid);
         }
 
+        blk_finish_plug(&plug);
+
         lock_page(page);
 
 page_hit: