From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f174.google.com (mail-wi0-f174.google.com [209.85.212.174]) by kanga.kvack.org (Postfix) with ESMTP id 0F3726B007D for ; Sun, 24 May 2015 13:49:10 -0400 (EDT) Received: by wibt6 with SMTP id t6so30441355wib.0 for ; Sun, 24 May 2015 10:49:09 -0700 (PDT) Received: from mout.kundenserver.de (mout.kundenserver.de. [212.227.17.10]) by mx.google.com with ESMTPS id cn6si14262623wjb.209.2015.05.24.10.49.07 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 24 May 2015 10:49:08 -0700 (PDT) From: Arnd Bergmann Subject: Re: [RFC PATCH 2/2] arm64: Implement vmalloc based thread_info allocator Date: Sun, 24 May 2015 19:49:01 +0200 Message-ID: <5992243.NYDGjLH37z@wuerfel> In-Reply-To: <1432483340-23157-1-git-send-email-jungseoklee85@gmail.com> References: <1432483340-23157-1-git-send-email-jungseoklee85@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: owner-linux-mm@kvack.org List-ID: To: linux-arm-kernel@lists.infradead.org Cc: Jungseok Lee , Catalin Marinas , barami97@gmail.com, Will Deacon , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Monday 25 May 2015 01:02:20 Jungseok Lee wrote: > Fork-routine sometimes fails to get a physically contiguous region for > thread_info on 4KB page system although free memory is enough. That is, > a physically contiguous region, which is currently 16KB, is not available > since system memory is fragmented. > > This patch tries to solve the problem as allocating thread_info memory > from vmalloc space, not 1:1 mapping one. The downside is one additional > page allocation in case of vmalloc. However, vmalloc space is large enough, > around 240GB, under a combination of 39-bit VA and 4KB page. Thus, it is > not a big tradeoff for fork-routine service. vmalloc has a rather large runtime cost. I'd argue that failing to allocate thread_info structures means something has gone very wrong. Can you describe the scenario that leads to fragmentation this bad? Could the stack size be reduced to 8KB perhaps? Arnd -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org