From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755977AbdCGTur (ORCPT ); Tue, 7 Mar 2017 14:50:47 -0500 Received: from bombadil.infradead.org ([65.50.211.133]:49663 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755194AbdCGTup (ORCPT ); Tue, 7 Mar 2017 14:50:45 -0500 Date: Tue, 7 Mar 2017 10:57:48 -0800 From: Matthew Wilcox To: Michal Hocko Cc: Andrew Morton , Al Viro , Vlastimil Babka , David Rientjes , Cristopher Lameter , linux-mm@kvack.org, LKML , Michal Hocko Subject: Re: [PATCH] mm, vmalloc: use __GFP_HIGHMEM implicitly Message-ID: <20170307185748.GU16328@bombadil.infradead.org> References: <20170307141020.29107-1-mhocko@kernel.org> <20170307182841.GS16328@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170307182841.GS16328@bombadil.infradead.org> User-Agent: Mutt/1.7.1 (2016-10-04) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 +#endif #define ___GFP_DMA32 0x04u #define ___GFP_MOVABLE 0x08u #define ___GFP_RECLAIMABLE 0x10u