Date: Tue, 21 Mar 2006 22:41:40 -0800
From: Andrew Morton <akpm@osdl.org>
To: Eric Dumazet <dada1@cosmosbay.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [RFC, PATCH] avoid some atomics in open()/close() for
 monothreaded processes
Message-Id: <20060321224140.7e40a380.akpm@osdl.org>
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Eric Dumazet <dada1@cosmosbay.com> wrote:
>
> Goal : Avoid some locking/unlocking 'struct files_struct'->file_lock for mono 
> threaded processes.
> 
> We define files_multithreaded() function .
> 
> static inline int files_multithreaded(const struct files_struct *files)
> {
>         return sizeof(files->file_lock) > 0 && atomic_read(&files->count) > 1;
> }

That's bascially sizeof(spinlock_t).  That's architecture dependent and
varies wildly according to the day of week.

It _might_ work in all situations - probably you checked that.  But I still
wouldn't do it because it might break in the future.  Let's be explicit and
stick the appropriate ifdefs in there.

I'd also consider renaming it to files_shared() - processes are
multithreaded, not data structures.

Once you're done with that we should change fget_light() and fput_light() to
use this helper.  Separate patch.

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