linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: fix comment of f2fs_evict

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Message-ID: <20190929021939.GA136917@architecture4>
Date:   Sun, 29 Sep 2019 10:20:52 +0800
From:   Gao Xiang <gaoxiang25@...wei.com>
To:     <linux-f2fs-devel@...ts.sourceforge.net>
CC:     Chao Yu <yuchao0@...wei.com>, Jaegeuk Kim <jaegeuk@...nel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>
Subject: Re: [f2fs-dev] [PATCH] f2fs: fix comment of f2fs_evict_inode

On Sun, Sep 29, 2019 at 08:53:05AM +0800, Chao Yu wrote:
> Hi Jaegeuk,
> 
> On 2019/9/28 2:31, Jaegeuk Kim wrote:
> > Hi Chao,
> > 
> > On 09/25, Chao Yu wrote:
> >> evict() should be called once i_count is zero, rather than i_nlinke
> >> is zero.
> >>
> >> Reported-by: Gao Xiang <gaoxiang25@...wei.com>
> >> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> >> ---
> >>  fs/f2fs/inode.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
> >> index db4fec30c30d..8262f4a483d3 100644
> >> --- a/fs/f2fs/inode.c
> >> +++ b/fs/f2fs/inode.c
> >> @@ -632,7 +632,7 @@ int f2fs_write_inode(struct inode *inode, struct writeback_control *wbc)
> >>  }
> >>  
> >>  /*
> >> - * Called at the last iput() if i_nlink is zero
> > 
> > I don't think this comment is wrong. You may be able to add on top of this.
> 
> It actually misleads the developer or user.
> 
> How do you think of:
> 
> "Called at the last iput() if i_count is zero, and will release all meta/data
> blocks allocated in the inode if i_nlink is zero"

(sigh... side note: I just took some time to check the original meaning
 out of curiosity. AFAIK, the above word was added in Linux-2.1.45 [1]
 due to ext2_delete_inode behavior, which is called when i_nlink == 0,
 and .delete_inode was gone in 2010 (commit 72edc4d0873b merge ext2
 delete_inode and clear_inode, switch to ->evict_inode()), it may be
 helpful to understand the story so I write here for later folks reference.
 And it's also good to just kill it. )

+
+/*
+ * Called at the last iput() if i_nlink is zero.
+ */
+void ext2_delete_inode (struct inode * inode)
+{
+	if (inode->i_ino == EXT2_ACL_IDX_INO ||
 	    inode->i_ino == EXT2_ACL_DATA_INO)
 		return;
 	inode->u.ext2_i.i_dtime	= CURRENT_TIME;
-	inode->i_dirt = 1;
+	mark_inode_dirty(inode);
 	ext2_update_inode(inode, IS_SYNC(inode));
 	inode->i_size = 0;
 	if (inode->i_blocks)
@@ -248,7 +258,7 @@
 	if (IS_SYNC(inode) || inode->u.ext2_i.i_osync)
 		ext2_sync_inode (inode);
 	else
-		inode->i_dirt = 1;
+		mark_inode_dirty(inode);
 	return result;
 }

+void iput(struct inode *inode)
 {
-	struct inode * inode = get_empty_inode();
+	if (inode) {
+		struct super_operations *op = NULL;
 
-	PIPE_BASE(*inode) = (char*)__get_free_page(GFP_USER);
-	if (!(PIPE_BASE(*inode))) {
-		iput(inode);
-		return NULL;
+		if (inode->i_sb && inode->i_sb->s_op)
+			op = inode->i_sb->s_op;
+		if (op && op->put_inode)
+			op->put_inode(inode);
+
+		spin_lock(&inode_lock);
+		if (!--inode->i_count) {
+			if (!inode->i_nlink) {
+				list_del(&inode->i_hash);
+				INIT_LIST_HEAD(&inode->i_hash);
+				if (op && op->delete_inode) {
+					void (*delete)(struct inode *) = op->delete_inode;
+					spin_unlock(&inode_lock);
+					delete(inode);
+					spin_lock(&inode_lock);
+				}
+			}
+			if (list_empty(&inode->i_hash)) {
+				list_del(&inode->i_list);
+				list_add(&inode->i_list, &inode_unused);
+			}
+		}
+		spin_unlock(&inode_lock);
 	}

[1] https://www.kernel.org/pub/linux/kernel/v2.1/patch-2.1.45.xz

Thanks,
Gao Xiang

> 
> Thanks,
> 
> > 
> >> + * Called at the last iput() if i_count is zero
> >>   */
> >>  void f2fs_evict_inode(struct inode *inode)
> >>  {
> >> -- 
> >> 2.18.0.rc1
> > .
> > 
> 
> 
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