Re: [PATCH] ext4: fix ext4_evict_inode() racing against workqueue processing code

[Zheng Liu <gnehzuil.liu@gmail.com>]

On Tue, Mar 26, 2013 at 01:52:51PM +0800, Zheng Liu wrote:
> Sorry for the late reply.
> 
> On Wed, Mar 20, 2013 at 10:45:23AM -0400, Theodore Ts'o wrote:
> > On Wed, Mar 20, 2013 at 09:14:42AM -0500, Eric Sandeen wrote:
> > > 
> > > As an aside, is there any reason to have "dioread_nolock" as an option
> > > at this point?  If it works now, would you ever *not* want it?
> > > 
> > > (granted it doesn't work with some journaling options etc, but that
> > > behavior could be automatic, w/o the need for special mount options).
> > 
> > The primary restriction is that diread_nolock doesn't work when fs
> > block size != page size.  If your proposal is that we automatically
> > enable diread_nolock when we can use it safely, that's definitely
> > something to consider for the next merge window.
> 
> Yes, I also think we can automatically enable dioread_nolock because it
> brings us some benefits.
> 
> BTW, I think there is an minor improvement for dio overwrite codepath
> with indirect-based file.  We don't need to take i_mutex in this
> condition just as we have done for extent-based file.  If a user mounts
> a ext2/3 file system with a ext4 kernel modules, he/she could get a
> lower latency.  But it seems that it would break dio semantic in ext2/3.
> Currently in ext2/3 if we issue a overwrite dio and then issue a read
> dio.  We will always read the latest data because we wait on i_mutex
> lock.  But after parallelizing overwite dio, this semantic might breaks.
> I re-read this doc but it seems that it doesn't describe this case.
                 ^^^

Ah, sorry, I forgot to paste the link here.
https://ext4.wiki.kernel.org/index.php/Clarifying_Direct_IO%27s_Semantics

Regards,
                                                - Zheng