From: Michal Hocko <mhocko@kernel.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>
Subject: Re: [PATCH] mm, vmalloc: use __GFP_HIGHMEM implicitly
Date: Wed, 8 Mar 2017 10:32:40 +0100 [thread overview]
Message-ID: <20170308093239.GE11028@dhcp22.suse.cz> (raw)
In-Reply-To: <20170307185748.GU16328@bombadil.infradead.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
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next prev parent reply other threads:[~2017-03-08 9:32 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-07 14:10 [PATCH] mm, vmalloc: use __GFP_HIGHMEM implicitly Michal Hocko
2017-03-07 18:28 ` Matthew Wilcox
2017-03-07 18:57 ` Matthew Wilcox
2017-03-08 7:37 ` Vlastimil Babka
2017-03-08 9:32 ` Michal Hocko [this message]
2017-03-07 23:08 ` Andrew Morton
2017-03-08 0:10 ` Matthew Wilcox
2017-03-08 9:22 ` Michal Hocko
2017-03-08 7:33 ` Vlastimil Babka
2017-03-08 9:26 ` Michal Hocko
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