From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751203AbdCHHis (ORCPT ); Wed, 8 Mar 2017 02:38:48 -0500 Received: from mx2.suse.de ([195.135.220.15]:35226 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750757AbdCHHip (ORCPT ); Wed, 8 Mar 2017 02:38:45 -0500 Subject: Re: [PATCH] mm, vmalloc: use __GFP_HIGHMEM implicitly To: Matthew Wilcox , Michal Hocko References: <20170307141020.29107-1-mhocko@kernel.org> <20170307182841.GS16328@bombadil.infradead.org> <20170307185748.GU16328@bombadil.infradead.org> Cc: Andrew Morton , Al Viro , David Rientjes , Cristopher Lameter , linux-mm@kvack.org, LKML , Michal Hocko From: Vlastimil Babka Message-ID: <1d8e9dd2-a542-250b-846f-5d1d7941a6b5@suse.cz> Date: Wed, 8 Mar 2017 08:37:57 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.1 MIME-Version: 1.0 In-Reply-To: <20170307185748.GU16328@bombadil.infradead.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/07/2017 07:57 PM, Matthew Wilcox wrote: > On Tue, Mar 07, 2017 at 10:28:41AM -0800, Matthew Wilcox wrote: >> On Tue, Mar 07, 2017 at 03:10:20PM +0100, Michal Hocko wrote: >>> This patch simply uses __GFP_HIGHMEM implicitly when allocating pages to >>> be mapped to the vmalloc space. Current users which add __GFP_HIGHMEM >>> are simplified and drop the flag. > > btw, I had another idea for GFP_HIGHMEM -- remove it when CONFIG_HIGHMEM > isn't enabled. Saves 26 bytes of .text and 64 bytes of .data on my > laptop's kernel build. What do you think? > > Also, I suspect the layout of bits is suboptimal from an assembly > language perspective. I still mostly care about x86 which doesn't > benefit, so I'm not inclined to do the work, but certainly ARM, PA-RISC, > SPARC and Itanium would all benefit from having frequently-used bits > (ie those used in GFP_KERNEL and GFP_ATOMIC) placed in the low 8 bits. > > diff --git a/include/linux/gfp.h b/include/linux/gfp.h > index 0fe0b6295ab5..d88cb532d7c8 100644 > --- a/include/linux/gfp.h > +++ b/include/linux/gfp.h > @@ -16,7 +16,11 @@ struct vm_area_struct; > > /* Plain integer GFP bitmasks. Do not use this directly. */ > #define ___GFP_DMA 0x01u > +#ifdef CONFIG_HIGHMEM > #define ___GFP_HIGHMEM 0x02u > +#else > +#define ___GFP_HIGHMEM 0x0u Make sure you don't break the users of __def_gfpflag_names e.g. format_flags(). IIRC zero is a terminator in the table. But the savings don't seem to be worth the trouble. > +#endif > #define ___GFP_DMA32 0x04u > #define ___GFP_MOVABLE 0x08u > #define ___GFP_RECLAIMABLE 0x10u >