From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx149.postini.com [74.125.245.149]) by kanga.kvack.org (Postfix) with SMTP id 9B82F6B0034 for ; Sun, 16 Jun 2013 00:27:11 -0400 (EDT) Message-ID: <1371356818.21896.114.camel@pasglop> Subject: Re: [PATCH 2/4] powerpc: Prepare to support kernel handling of IOMMU map/unmap From: Benjamin Herrenschmidt Date: Sun, 16 Jun 2013 14:26:58 +1000 In-Reply-To: <1370412673-1345-3-git-send-email-aik@ozlabs.ru> References: <1370412673-1345-1-git-send-email-aik@ozlabs.ru> <1370412673-1345-3-git-send-email-aik@ozlabs.ru> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Alexey Kardashevskiy Cc: linuxppc-dev@lists.ozlabs.org, David Gibson , Alexander Graf , Paul Mackerras , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org, "linux-mm@kvack.org" > +#if defined(CONFIG_SPARSEMEM_VMEMMAP) || defined(CONFIG_FLATMEM) > +int realmode_get_page(struct page *page) > +{ > + if (PageCompound(page)) > + return -EAGAIN; > + > + get_page(page); > + > + return 0; > +} > +EXPORT_SYMBOL_GPL(realmode_get_page); > + > +int realmode_put_page(struct page *page) > +{ > + if (PageCompound(page)) > + return -EAGAIN; > + > + if (!atomic_add_unless(&page->_count, -1, 1)) > + return -EAGAIN; > + > + return 0; > +} > +EXPORT_SYMBOL_GPL(realmode_put_page); > +#endif Several worries here, mostly that if the generic code ever changes (something gets added to get_page() that makes it no-longer safe for use in real mode for example, or some other condition gets added to put_page()), we go out of sync and potentially end up with very hard and very subtle bugs. It might be worth making sure that: - This is reviewed by some generic VM people (and make sure they understand why we need to do that) - A comment is added to get_page() and put_page() to make sure that if they are changed in any way, dbl check the impact on our realmode_get_page() (or "ping" us to make sure things are still ok). Cheers, Ben. -- 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