From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from moutng.kundenserver.de (moutng.kundenserver.de [212.227.126.186]) by ozlabs.org (Postfix) with ESMTP id 12973DDDE3 for ; Tue, 16 Dec 2008 02:43:54 +1100 (EST) From: Arnd Bergmann To: linuxppc-dev@ozlabs.org Subject: Re: [PATCH 6/16] powerpc/mm: Split mmu_context handling v3 Date: Mon, 15 Dec 2008 16:43:44 +0100 References: <20081215054530.4835FDE00C@ozlabs.org> In-Reply-To: <20081215054530.4835FDE00C@ozlabs.org> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Message-Id: <200812151643.44944.arnd@arndb.de> Cc: Kumar Gala List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Monday 15 December 2008, Benjamin Herrenschmidt wrote: > +/* > + * On 32-bit PowerPC 6xx/7xx/7xxx CPUs, we use a set of 16 VSIDs > + * (virtual segment identifiers) for each context. Although the > + * hardware supports 24-bit VSIDs, and thus >1 million contexts, > + * we only use 32,768 of them. That is ample, since there can be > + * at most around 30,000 tasks in the system anyway, and it means > + * that we can use a bitmap to indicate which contexts are in use. > + * Using a bitmap means that we entirely avoid all of the problems > + * that we used to have when the context number overflowed, > + * particularly on SMP systems. > + * -- paulus. > + */ Didn't we lift the limit to 30,000 tasks at some point? The comment in linux/threads.h mentions that the PID space goes up to 4 million. What does actually happen when we increase pid_max to beyond 32768 on those systems and try to use them? Is there another limit in place? Arnd <><