From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: Christoph Lameter <clameter@sgi.com>
Cc: linux-ia64@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [RFC] virtual memmap for sparsemem [2/2] for ia64.
Date: Fri, 20 Oct 2006 10:35:34 +0900 [thread overview]
Message-ID: <20061020103534.35a92813.kamezawa.hiroyu@jp.fujitsu.com> (raw)
In-Reply-To: <Pine.LNX.4.64.0610190940140.8072@schroedinger.engr.sgi.com>
On Thu, 19 Oct 2006 09:41:19 -0700 (PDT)
Christoph Lameter <clameter@sgi.com> wrote:
> On Thu, 19 Oct 2006, KAMEZAWA Hiroyuki wrote:
>
> > +config ARCH_VMEMMAP_SPARSEMEM_SUPPORT
> > + def_bool y
> > + depends on PGTABLE_4 && ARCH_SPARSEMEM_ENABLE
>
> Why do you need to depend on 4 level page tables?
>
It's based on how big page-table can map. (I'm sorry if my calculation is wrong..)
Maximun phyisical address size of Itanium2 looks 50bits. Then, we need
sizeof (struct page) * (50 - PAGE_SHIFT) size of virtual address space.
#define PTRS_PER_PTD_SHIFT (PAGE_SHIFT-3)
#define PTRS_PER_PTE (__IA64_UL(1) << (PTRS_PER_PTD_SHIFT))
#define PMD_SHIFT (PAGE_SHIFT + (PTRS_PER_PTD_SHIFT))
#define PUD_SHIFT (PMD_SHIFT + (PTRS_PER_PTD_SHIFT))
#ifdef CONFIG_PGTABLE_4
#define PGDIR_SHIFT (PUD_SHIFT + (PTRS_PER_PTD_SHIFT))
#else
#define PGDIR_SHIFT (PMD_SHIFT + (PTRS_PER_PTD_SHIFT))
#endif
Then, considering PAGE_SHIFT=14 case,
4-level-page-table mapsize:(1 << (4 * PAGE_SHIFT - 9) -> (1 << 47)
3-level-page-table mapsize:(1 << (3 * PAGE_SHIFT - 6) -> (1 << 36)
we need 4 level.
> > +#if defined(CONFIG_VIRTUAL_MEM_MAP) || defined(CONFIG_VMEMMAP_SPARSEMEM)
> > unsigned long vmalloc_end = VMALLOC_END_INIT;
>
> I'd rather stop tinkering around with vmalloc_end. See my patches that I
> posted last week to realize virtual memmap.
Okay, I'll look into.
-Kame
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next prev parent reply other threads:[~2006-10-20 1:35 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-10-19 8:23 KAMEZAWA Hiroyuki
2006-10-19 15:23 ` Andy Whitcroft
2006-10-20 1:20 ` KAMEZAWA Hiroyuki
2006-10-19 16:41 ` Christoph Lameter
2006-10-20 1:35 ` KAMEZAWA Hiroyuki [this message]
2006-10-20 1:45 ` Christoph Lameter
2006-10-20 2:08 ` KAMEZAWA Hiroyuki
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