f2fs: reduce unncessary locking pages during read

This patch reduces redundant locking and unlocking pages during read operations.
In f2fs_readpage, let's use wait_on_page_locked() instead of lock_page.
And then, when we need to modify any data finally, let's lock the page so that
we can avoid lock contention.

[readpage rule]
- The f2fs_readpage returns unlocked page, or released page too in error cases.
- Its caller should handle read error, -EIO, after locking the page, which
  indicates read completion.
- Its caller should check PageUptodate after grab_cache_page.

Signed-off-by: Changman Lee <cm224.lee@samsung.com>
Reviewed-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

4 files changed, 91 insertions, 68 deletions

diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index 2b6fc131e2ce..d947e66ee8a8 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -57,13 +57,15 @@ repeat:
                 cond_resched();
                 goto repeat;
         }
-        if (f2fs_readpage(sbi, page, index, READ_SYNC)) {
-                f2fs_put_page(page, 1);
+        if (PageUptodate(page))
+                goto out;
+
+        if (f2fs_readpage(sbi, page, index, READ_SYNC))
                 goto repeat;
-        }
-        mark_page_accessed(page);
 
-        /* We do not allow returning an errorneous page */
+        lock_page(page);
+out:
+        mark_page_accessed(page);
         return page;
 }
 
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 277966a8547a..c8e20b618913 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -199,12 +199,17 @@ struct page *find_data_page(struct inode *inode, pgoff_t index)
         if (!page)
                 return ERR_PTR(-ENOMEM);
 
+        if (PageUptodate(page)) {
+                unlock_page(page);
+                return page;
+        }
+
         err = f2fs_readpage(sbi, page, dn.data_blkaddr, READ_SYNC);
-        if (err) {
-                f2fs_put_page(page, 1);
-                return ERR_PTR(err);
+        wait_on_page_locked(page);
+        if (!PageUptodate(page)) {
+                f2fs_put_page(page, 0);
+                return ERR_PTR(-EIO);
         }
-        unlock_page(page);
         return page;
 }
 
@@ -241,9 +246,13 @@ struct page *get_lock_data_page(struct inode *inode, pgoff_t index)
         BUG_ON(dn.data_blkaddr == NULL_ADDR);
 
         err = f2fs_readpage(sbi, page, dn.data_blkaddr, READ_SYNC);
-        if (err) {
-                f2fs_put_page(page, 1);
+        if (err)
                 return ERR_PTR(err);
+
+        lock_page(page);
+        if (!PageUptodate(page)) {
+                f2fs_put_page(page, 1);
+                return ERR_PTR(-EIO);
         }
         return page;
 }
@@ -283,14 +292,17 @@ struct page *get_new_data_page(struct inode *inode, pgoff_t index,
 
         if (dn.data_blkaddr == NEW_ADDR) {
                 zero_user_segment(page, 0, PAGE_CACHE_SIZE);
+                SetPageUptodate(page);
         } else {
                 err = f2fs_readpage(sbi, page, dn.data_blkaddr, READ_SYNC);
-                if (err) {
-                        f2fs_put_page(page, 1);
+                if (err)
                         return ERR_PTR(err);
+                lock_page(page);
+                if (!PageUptodate(page)) {
+                        f2fs_put_page(page, 1);
+                        return ERR_PTR(-EIO);
                 }
         }
-        SetPageUptodate(page);
 
         if (new_i_size &&
                 i_size_read(inode) < ((index + 1) << PAGE_CACHE_SHIFT)) {
@@ -325,22 +337,14 @@ static void read_end_io(struct bio *bio, int err)
 
 /*
  * Fill the locked page with data located in the block address.
- * Read operation is synchronous, and caller must unlock the page.
+ * Return unlocked page.
  */
 int f2fs_readpage(struct f2fs_sb_info *sbi, struct page *page,
                                         block_t blk_addr, int type)
 {
         struct block_device *bdev = sbi->sb->s_bdev;
-        bool sync = (type == READ_SYNC);
         struct bio *bio;
 
-        /* This page can be already read by other threads */
-        if (PageUptodate(page)) {
-                if (!sync)
-                        unlock_page(page);
-                return 0;
-        }
-
         down_read(&sbi->bio_sem);
 
         /* Allocate a new bio */
@@ -354,18 +358,12 @@ int f2fs_readpage(struct f2fs_sb_info *sbi, struct page *page,
                 kfree(bio->bi_private);
                 bio_put(bio);
                 up_read(&sbi->bio_sem);
+                f2fs_put_page(page, 1);
                 return -EFAULT;
         }
 
         submit_bio(type, bio);
         up_read(&sbi->bio_sem);
-
-        /* wait for read completion if sync */
-        if (sync) {
-                lock_page(page);
-                if (PageError(page))
-                        return -EIO;
-        }
         return 0;
 }
 
@@ -636,18 +634,22 @@ static int f2fs_write_begin(struct file *file, struct address_space *mapping,
 
                 /* Reading beyond i_size is simple: memset to zero */
                 zero_user_segments(page, 0, start, end, PAGE_CACHE_SIZE);
-                return 0;
+                goto out;
         }
 
         if (dn.data_blkaddr == NEW_ADDR) {
                 zero_user_segment(page, 0, PAGE_CACHE_SIZE);
         } else {
                 err = f2fs_readpage(sbi, page, dn.data_blkaddr, READ_SYNC);
-                if (err) {
-                        f2fs_put_page(page, 1);
+                if (err)
                         return err;
+                lock_page(page);
+                if (!PageUptodate(page)) {
+                        f2fs_put_page(page, 1);
+                        return -EIO;
                 }
         }
+out:
         SetPageUptodate(page);
         clear_cold_data(page);
         return 0;
diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index a3cb1ff34f8e..9e6ed6708fa8 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -100,10 +100,13 @@ static void ra_nat_pages(struct f2fs_sb_info *sbi, int nid)
                 page = grab_cache_page(mapping, index);
                 if (!page)
                         continue;
-                if (f2fs_readpage(sbi, page, index, READ)) {
+                if (PageUptodate(page)) {
                         f2fs_put_page(page, 1);
                         continue;
                 }
+                if (f2fs_readpage(sbi, page, index, READ))
+                        continue;
+
                 f2fs_put_page(page, 0);
         }
 }
@@ -851,8 +854,16 @@ static int read_node_page(struct page *page, int type)
 
         get_node_info(sbi, page->index, &ni);
 
-        if (ni.blk_addr == NULL_ADDR)
+        if (ni.blk_addr == NULL_ADDR) {
+                f2fs_put_page(page, 1);
                 return -ENOENT;
+        }
+
+        if (PageUptodate(page)) {
+                unlock_page(page);
+                return 0;
+        }
+
         return f2fs_readpage(sbi, page, ni.blk_addr, type);
 }
 
@@ -865,19 +876,18 @@ void ra_node_page(struct f2fs_sb_info *sbi, nid_t nid)
         struct page *apage;
 
         apage = find_get_page(mapping, nid);
-        if (apage && PageUptodate(apage))
-                goto release_out;
+        if (apage && PageUptodate(apage)) {
+                f2fs_put_page(apage, 0);
+                return;
+        }
         f2fs_put_page(apage, 0);
 
         apage = grab_cache_page(mapping, nid);
         if (!apage)
                 return;
 
-        if (read_node_page(apage, READA))
-                unlock_page(apage);
-
-release_out:
-        f2fs_put_page(apage, 0);
+        if (read_node_page(apage, READA) == 0)
+                f2fs_put_page(apage, 0);
         return;
 }
 
@@ -892,11 +902,14 @@ struct page *get_node_page(struct f2fs_sb_info *sbi, pgoff_t nid)
                 return ERR_PTR(-ENOMEM);
 
         err = read_node_page(page, READ_SYNC);
-        if (err) {
-                f2fs_put_page(page, 1);
+        if (err)
                 return ERR_PTR(err);
-        }
 
+        lock_page(page);
+        if (!PageUptodate(page)) {
+                f2fs_put_page(page, 1);
+                return ERR_PTR(-EIO);
+        }
         BUG_ON(nid != nid_of_node(page));
         mark_page_accessed(page);
         return page;
@@ -928,11 +941,8 @@ repeat:
                 goto page_hit;
 
         err = read_node_page(page, READ_SYNC);
-        unlock_page(page);
-        if (err) {
-                f2fs_put_page(page, 0);
+        if (err)
                 return ERR_PTR(err);
-        }
 
         /* Then, try readahead for siblings of the desired node */
         end = start + MAX_RA_NODE;
@@ -957,6 +967,7 @@ page_hit:
                 f2fs_put_page(page, 1);
                 goto repeat;
         }
+        mark_page_accessed(page);
         return page;
 }
 
@@ -1473,23 +1484,24 @@ int restore_node_summary(struct f2fs_sb_info *sbi,
         sum_entry = &sum->entries[0];
 
         for (i = 0; i < last_offset; i++, sum_entry++) {
+                /*
+                 * In order to read next node page,
+                 * we must clear PageUptodate flag.
+                 */
+                ClearPageUptodate(page);
+
                 if (f2fs_readpage(sbi, page, addr, READ_SYNC))
                         goto out;
 
+                lock_page(page);
                 rn = (struct f2fs_node *)page_address(page);
                 sum_entry->nid = rn->footer.nid;
                 sum_entry->version = 0;
                 sum_entry->ofs_in_node = 0;
                 addr++;
-
-                /*
-                 * In order to read next node page,
-                 * we must clear PageUptodate flag.
-                 */
-                ClearPageUptodate(page);
         }
-out:
         unlock_page(page);
+out:
         __free_pages(page, 0);
         return 0;
 }
diff --git a/fs/f2fs/recovery.c b/fs/f2fs/recovery.c
index 6b82e2034cfd..2d86eb26c493 100644
--- a/fs/f2fs/recovery.c
+++ b/fs/f2fs/recovery.c
@@ -112,11 +112,16 @@ static int find_fsync_dnodes(struct f2fs_sb_info *sbi, struct list_head *head)
         while (1) {
                 struct fsync_inode_entry *entry;
 
-                if (f2fs_readpage(sbi, page, blkaddr, READ_SYNC))
+                err = f2fs_readpage(sbi, page, blkaddr, READ_SYNC);
+                if (err)
                         goto out;
 
-                if (cp_ver != cpver_of_node(page))
-                        goto out;
+                lock_page(page);
+
+                if (cp_ver != cpver_of_node(page)) {
+                        err = -EINVAL;
+                        goto unlock_out;
+                }
 
                 if (!is_fsync_dnode(page))
                         goto next;
@@ -131,7 +136,7 @@ static int find_fsync_dnodes(struct f2fs_sb_info *sbi, struct list_head *head)
                         if (IS_INODE(page) && is_dent_dnode(page)) {
                                 if (recover_inode_page(sbi, page)) {
                                         err = -ENOMEM;
-                                        goto out;
+                                        goto unlock_out;
                                 }
                         }
 
@@ -139,14 +144,14 @@ static int find_fsync_dnodes(struct f2fs_sb_info *sbi, struct list_head *head)
                         entry = kmem_cache_alloc(fsync_entry_slab, GFP_NOFS);
                         if (!entry) {
                                 err = -ENOMEM;
-                                goto out;
+                                goto unlock_out;
                         }
 
                         entry->inode = f2fs_iget(sbi->sb, ino_of_node(page));
                         if (IS_ERR(entry->inode)) {
                                 err = PTR_ERR(entry->inode);
                                 kmem_cache_free(fsync_entry_slab, entry);
-                                goto out;
+                                goto unlock_out;
                         }
 
                         list_add_tail(&entry->list, head);
@@ -155,15 +160,15 @@ static int find_fsync_dnodes(struct f2fs_sb_info *sbi, struct list_head *head)
                 if (IS_INODE(page)) {
                         err = recover_inode(entry->inode, page);
                         if (err)
-                                goto out;
+                                goto unlock_out;
                 }
 next:
                 /* check next segment */
                 blkaddr = next_blkaddr_of_node(page);
-                ClearPageUptodate(page);
         }
-out:
+unlock_out:
         unlock_page(page);
+out:
         __free_pages(page, 0);
         return err;
 }
@@ -319,8 +324,10 @@ static void recover_data(struct f2fs_sb_info *sbi,
                 if (f2fs_readpage(sbi, page, blkaddr, READ_SYNC))
                         goto out;
 
+                lock_page(page);
+
                 if (cp_ver != cpver_of_node(page))
-                        goto out;
+                        goto unlock_out;
 
                 entry = get_fsync_inode(head, ino_of_node(page));
                 if (!entry)
@@ -336,10 +343,10 @@ static void recover_data(struct f2fs_sb_info *sbi,
 next:
                 /* check next segment */
                 blkaddr = next_blkaddr_of_node(page);
-                ClearPageUptodate(page);
         }
-out:
+unlock_out:
         unlock_page(page);
+out:
         __free_pages(page, 0);
 
         allocate_new_segments(sbi);