This patch reduces the lock granularity during write_begin.
When the system is under memory pressure, it would be better to reduce
the locking time for the data pages.

Signed-off-by: Jaegeuk Kim <jaegeuk....@samsung.com>
---
 fs/f2fs/data.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 91ff104..a7bb98f 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -909,6 +909,10 @@ repeat:
        page = grab_cache_page_write_begin(mapping, index, flags);
        if (!page)
                return -ENOMEM;
+
+       /* to avoid latency during memory pressure */
+       unlock_page(page);
+
        *pagep = page;
 
        if (f2fs_has_inline_data(inode) && (pos + len) <= MAX_INLINE_DATA)
@@ -920,10 +924,18 @@ repeat:
        f2fs_unlock_op(sbi);
 
        if (err) {
-               f2fs_put_page(page, 1);
+               f2fs_put_page(page, 0);
                return err;
        }
 inline_data:
+       lock_page(page);
+       if (unlikely(page->mapping != mapping)) {
+               f2fs_put_page(page, 1);
+               goto repeat;
+       }
+
+       f2fs_wait_on_page_writeback(page, DATA);
+
        if ((len == PAGE_CACHE_SIZE) || PageUptodate(page))
                return 0;
 
-- 
1.8.4.474.g128a96c

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