linux-kernel - Re: [Patch] Scale pidhash_shift/pidhash_size up based on num_possible

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Date:	Thu, 31 Jul 2008 15:04:56 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Robin Holt <holt@....com>
Cc:	linux-kernel@...r.kernel.org, Pavel Emelyanov <xemul@...nvz.org>,
	Oleg Nesterov <oleg@...sign.ru>,
	Sukadev Bhattiprolu <sukadev@...ibm.com>,
	Paul Menage <menage@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [Patch] Scale pidhash_shift/pidhash_size up based on num_possible_cpus().

Robin Holt <holt@....com> writes:

> Like so???
>
> I have not tested this yet.

Looks reasonable to me.

In what circumstances was the lookup in the pid hash table with
long changes causing a performance slowdown?.  We don't perform
a lot of lookups.


> -	pidhash_shift = min(12, pidhash_shift);
> +	pidhash_shift = min(fls(PID_MAX_LIMIT) - 6, pidhash_shift);
>  	pidhash_size = 1 << pidhash_shift;
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