linux-kernel - Re: [PATCH] speed up /proc/pid/stat, statm

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Message-ID: <1328075682.2617.48.camel@edumazet-laptop>
Date:	Wed, 01 Feb 2012 06:54:42 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] speed up /proc/pid/stat, statm

Le mercredi 01 février 2012 à 08:55 +0900, KAMEZAWA Hiroyuki a écrit :

> seq_xxxx functions set m->count == m->size when it finds possible buffer overflow.
> If m->count == m->size after ->show(), buffer will be freed and twice size buffer
> will be re-allocated, and retry.
> 
> If we don't set m->count == m->size here, following seq_putc() will succeed and
> we'll see corrupted outputs.

I suppose we could define a self documented helper

void seq_overflow(struct seq_file *seq)
{
	seq->count = seq->size;
}

Or if we were counting the approximate number of missing bytes, we could
avoid some iterations of the "double size buffer".

(letting seq->count going above seq->size, but not allowing buffer
overflow of course !)



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