linux-kernel - Re: [PATCH] VFS: Go through the LRU list of inode from head

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Message-ID: <20120626033546.Horde.D-JZIpir309P6WZSsiFCifA@imap.linux.ibm.com>
Date:	Tue, 26 Jun 2012 03:35:46 -0400
From:	mc@...ux.vnet.ibm.com
To:	Jan Kara <jack@...e.cz>
Cc:	Al Viro <viro@...iv.linux.org.uk>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] VFS: Go through the LRU list of inode from head


Quoting Jan Kara <jack@...e.cz>:

> On Thu 21-06-12 17:00:27, Cong Meng wrote:
>> Go through the LRU list of inode from head.
>>
>> (I'm not sure whether there is any trick here I doesn't get.  If yes,
>> any one could explain it)
>   Look at inode_lru_list_add(). It adds at the head of the list. So you
> should take from the tail to get the least recently used element...

I still have a quetion about the subsequent code and comment:

inode = list_entry(sb->s_inode_lru.prev, struct inode, i_lru);
/*
  * we are inverting the sb->s_inode_lru_lock/inode->i_lock here,
  * so use a trylock. If we fail to get the lock, just move the
  * inode to the back of the list so we don't spin on it.
  */
if (!spin_trylock(&inode->i_lock)) {
         list_move_tail(&inode->i_lru, &sb->s_inode_lru);
         continue;
}

Shouldn't the inode be moved to the head to avoid spin on it?
I note that list_move was replaced by list_move_tail purposely in a commit.


and below piece of code (at the bottom of prune_icache_sb()):

if (inode != list_entry(sb->s_inode_lru.next,
                         struct inode, i_lru))
         continue;       /* wrong inode or list_empty */

Should the inode be compared against to the tail of the list other  
than the head
after re-get the lru lock?

thanks.
cong.
>
> 								Honza
>
>>
>> Signed-off-by: Cong Meng <mc@...ux.vnet.ibm.com>
>> ---
>>  fs/inode.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/fs/inode.c b/fs/inode.c
>> index 775cbab..aac8449 100644
>> --- a/fs/inode.c
>> +++ b/fs/inode.c
>> @@ -704,7 +704,7 @@ void prune_icache_sb(struct super_block *sb,  
>> int nr_to_scan)
>>  		if (list_empty(&sb->s_inode_lru))
>>  			break;
>>
>> -		inode = list_entry(sb->s_inode_lru.prev, struct inode, i_lru);
>> +		inode = list_entry(sb->s_inode_lru.next, struct inode, i_lru);
>>
>>  		/*
>>  		 * we are inverting the sb->s_inode_lru_lock/inode->i_lock here,
>> --
>> 1.7.5.4
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
>> the body of a message to majordomo@...r.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> --
> Jan Kara <jack@...e.cz>
> SUSE Labs, CR



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