Re: [PATCH 18/23] vfs: Teach epoll to use file_hotplug_lock

[Eric W. Biederman]

Davide Libenzi <davidel@xxxxxxxxxxxxxxx> writes:

> On Tue, 2 Jun 2009, Eric W. Biederman wrote:
>
>> I am not clear what problem you have.
>> 
>> Is it the sprinkling the code that takes and removes the lock?  Just
>> the VFS needs to be involved with that.  It is a slightly larger
>> surface area than doing the work inside the file operations as we
>> sometimes call the same method from 3-4 different places but it is
>> definitely a bounded problem.
>> 
>> Is it putting in the handful lines per subsystem to actually use this
>> functionality?  At that level something generic that is maintained
>> outside of the subsystem is better than the mess we have with 4-5
>> different implementations in the subsystems that need it, each having
>> a different assortment of bugs.
>
> Come on, only in the open fast path, there are at least two spin 
> lock/unlock and two atomic ops. Without even starting to count all the 
> extra branches and software added.
> Is this stuff *really* needed, or we can faitly happily live w/out?

????

What code are you talking about?

To the open path a few memory writes and a smp_wmb.  No atomics and no
spin lock/unlocks.

Are you complaining because I retain the file_list?

Eric
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