Re: [RFC PATCH 2/4] xfs: create function to scan and clear EOFBLOCKS inodes

Brian Foster
2012-09-05T12:22:31Z

On 09/05/2012 02:42 AM, Dave Chinner wrote:
> On Tue, Sep 04, 2012 at 10:10:00AM -0400, Brian Foster wrote:
>> On 09/03/2012 01:06 AM, Dave Chinner wrote:
>>> On Mon, Aug 27, 2012 at 03:51:49PM -0400, Brian Foster wrote:
>> ...
>>>> +/*
>>>> + * Handle an EOFBLOCKS tagged inode. If this is a forced scan, we wait on the
>>>> + * iolock ourselves rather than rely on the trylock in xfs_free_eofblocks().
>>>> + *
>>>> + * We rely on the output parameter from xfs_free_eofblocks() to determine
>>>> + * whether we should clear the tag because in the trylock case, it could have
>>>> + * skipped the inode due to lock contention.
>>>> + */
>>>> +STATIC int
>>>> +xfs_inode_free_eofblocks(
>>>> + struct xfs_inode *ip,
>>>> + int flags)
>>>> +{
>>>> + int ret = 0;
>>>> + bool freed = false;
>>>> + bool wait_iolock = (flags & EOFBLOCKS_WAIT) ? true : false;
>>>> +
>>>> + if (wait_iolock)
>>>> + xfs_ilock(ip, XFS_IOLOCK_EXCL);
>>>
>>> Why do we need the IO lock here? xfs_free_eofblocks() does all the
>>> necessary locking....
>>>
>>
>> This was for the wait case (e.g., xfs_free_eofblocks() does a trylock
>> on the IO lock and we want to wait for the lock in this case).
>
> Does it really matter if we can't get the iolock and skip the inode?
>

Well I thought that was the point of the force/wait scan as opposed to
the best effort scan. But...

> Note that xfs_inode_ag_walk() will keep a skipped count if you
> return EAGAIN, and re-run the walk on the AG if any inodes are
> skipped. This is done to prevent blocking on locks slowing down the
> scan - instead of blocking we move on to the next inode, and revist
> the blocked inodes again in a later pass.
>
> IOWs, if you convert the code to use the generic walk and make
> xfs_free_eofblocks() return EAGAIN when it can't get the io lock,
> you get the retry for free...
>

This sounds more efficient. ;) I'll move it to this approach. Thanks.

Brian

> Cheers,
>
> Dave.