Re: [PATCH 04/23] vfs: Introduce infrastructure for revoking a file

[Eric W. Biederman]

Nick Piggin <npiggin@xxxxxxx> writes:

>> In addition for a complete solution we need:
>> - A reliable way the file structures that we need to revoke.
>> - To wait for but not tamper with ongoing file creation and cleanup.
>> - A guarantee that all with user space controlled duration are removed.
>> 
>> The file_hotplug_lock has a very unique implementation necessitated by
>> the need to have no performance impact on existing code.  Classic locking
>
> Well, it isn't no performance impact. Function calls, branches, icache
> and dcache...

Practically none.

Everything I could measure was in the noise.  It is cheaper than any serializing
locking primitive.  I ran both lmbench and did some microbenchmark testing.
So I know on the fast path the overhead is minimal.  Certainly less than  what
we are doing in sysfs and proc today.

Eric

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