From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <owner-linux-mm@kvack.org>
Received: from mail-wm0-f71.google.com (mail-wm0-f71.google.com [74.125.82.71])
	by kanga.kvack.org (Postfix) with ESMTP id 1DF0E6B039F
	for <linux-mm@kvack.org>; Wed,  8 Mar 2017 04:32:43 -0500 (EST)
Received: by mail-wm0-f71.google.com with SMTP id u9so9291195wme.6
        for <linux-mm@kvack.org>; Wed, 08 Mar 2017 01:32:43 -0800 (PST)
Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15])
        by mx.google.com with ESMTPS id a143si4102910wme.44.2017.03.08.01.32.41
        for <linux-mm@kvack.org>
        (version=TLS1 cipher=AES128-SHA bits=128/128);
        Wed, 08 Mar 2017 01:32:41 -0800 (PST)
Date: Wed, 8 Mar 2017 10:32:40 +0100
From: Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH] mm, vmalloc: use __GFP_HIGHMEM implicitly
Message-ID: <20170308093239.GE11028@dhcp22.suse.cz>
References: <20170307141020.29107-1-mhocko@kernel.org>
 <20170307182841.GS16328@bombadil.infradead.org>
 <20170307185748.GU16328@bombadil.infradead.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20170307185748.GU16328@bombadil.infradead.org>
Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>, Al Viro <viro@zeniv.linux.org.uk>, Vlastimil Babka <vbabka@suse.cz>, David Rientjes <rientjes@google.com>, Cristopher Lameter <cl@linux.com>, linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>

On Tue 07-03-17 10:57:48, 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?

I wouldn't be opposed. The downside would be a slight confusion when
printing gfp flags but we already have this for ___GFP_NOLOCKDEP ;)

> 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.

be careful that there is some elaborate logic around low gfp bits to map
to proper zones and ALLOC_ constants.

> 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

Anyway, thanks for your review!
-- 
Michal Hocko
SUSE Labs

--
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: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>