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Message-ID: <20170307185748.GU16328@bombadil.infradead.org>
Date: Tue, 7 Mar 2017 10:57:48 -0800
From: Matthew Wilcox <willy@...radead.org>
To: Michal Hocko <mhocko@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Al Viro <viro@...iv.linux.org.uk>,
Vlastimil Babka <vbabka@...e.cz>,
David Rientjes <rientjes@...gle.com>,
Cristopher Lameter <cl@...ux.com>, linux-mm@...ck.org,
LKML <linux-kernel@...r.kernel.org>,
Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH] mm, vmalloc: use __GFP_HIGHMEM implicitly
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
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