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Subject: RE: [patch] fix ia64 hugetlb_free_pgd_range
Date: Thu, 23 Feb 2006 22:30:39 -0800
Message-ID: <B05667366EE6204181EABE9C1B1C0EB509C43438@scsmsx401.amr.corp.intel.com>
Thread-Topic: [patch] fix ia64 hugetlb_free_pgd_range
Thread-Index: AcY4+CdGKPryTO8pQb+SyAjC4nSbzgAEp2yQ
From: "Chen, Kenneth W" <kenneth.w.chen@intel.com>
To: "David Gibson" <david@gibson.dropbear.id.au>
Cc: "Hugh Dickins" <hugh@veritas.com>, "Luck, Tony" <tony.luck@intel.com>,
       <linux-ia64@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Sender: linux-kernel-owner@vger.kernel.org
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David Gibson wrote on Thursday, February 23, 2006 8:06 PM
> But I don't see how not transforming them sometimes can be correct.
> Suppose 'floor' is only a little way below 'addr' - addr will be
> shifted down, but floor won't, so floor may now be above addr, which
> will cause weird results.
> 
> Afaict the *only* thing floor and ceiling are used for is bounds
> checking the address range we're examining.  How can that ever be
> right if one address has been scaled down, but the other hasn't.

The scale down isn't exactly on every address bits.  Top 3 bits of
virtual address are preserved.

#define htlbpage_to_page(x)    (((unsigned long) REGION_NUMBER(x) << 61)
                                 | (REGION_OFFSET(x) >>
(HPAGE_SHIFT-PAGE_SHIFT)))

So scaled address for a hugetlb address will never be below unscaled
normal page address.  That is adjusted addr will never below unchanged
floor.

- Ken
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