Re: [PATCH] removes filp_count_lock and changes nr_files type to atomic_t

[Eric Dumazet <dada1@cosmosbay.com>]

Nick Piggin a écrit :

> OK, well I would prefer you do the proper atomic operations throughout
> where it "really matters" in file_table.c, and do your lazy synchronize
> with just the sysctl exported value.
> 

But... I got complains about atomic_read(&counter) being 'an atomic op' 
(untrue), so my second patch just doesnt touch the path where nr_files was read.

Furthermore, a lazy sync would mean to change sysctl proc_handler for 
"file-nr" to perform a synchronize before calling proc_dointvec, this would be 
really obscure.

> Unless the fs people had a problem with that.
> 
> And you may as well get rid of the atomic_inc_return which can be more
> expensive on some platforms and doesn't buy you much.
>   atomic_inc;
>   atomic_read;
> Should be enough if you don't care about lost updates here, yeah?
> 

You mean :

atomic_inc(&counter);
lazeyvalue = atomic_read(&counter);

instead of

lazeyvalue = atomic_inc_return(&counter);

In fact I couldnt find one architecture where the later would be more expensive.

> Nick
> 

Eric