linux-kernel - Re: [PATCH 1/3] Revert "thp: make MADV_HUGEPAGE check for mm->def

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Date:	Fri, 31 Jan 2014 14:52:24 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Alex Thorlton <athorlton@....com>
Cc:	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
	Gerald Schaefer <gerald.schaefer@...ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Sasha Levin <sasha.levin@...cle.com>, linux390@...ibm.com,
	linux-s390@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 1/3] Revert
 "thp: make MADV_HUGEPAGE check for mm->def_flags"

On Fri, 31 Jan 2014 12:23:43 -0600 Alex Thorlton <athorlton@....com> wrote:

> This reverts commit 8e72033f2a489b6c98c4e3c7cc281b1afd6cb85cm, and adds

'm' is not a hex digit ;)

> in code to fix up any issues caused by the revert.
> 
> The revert is necessary because hugepage_madvise would return -EINVAL
> when VM_NOHUGEPAGE is set, which will break subsequent chunks of this
> patch set.

This is a bit skimpy.  Why doesn't the patch re-break kvm-on-s390?

it would be nice to have a lot more detail here, please.  What was the
intent of 8e72033f2a48, how this patch retains 8e72033f2a48's behavior,
etc.

> --- a/arch/s390/mm/pgtable.c
> +++ b/arch/s390/mm/pgtable.c
> @@ -504,6 +504,9 @@ static int gmap_connect_pgtable(unsigned long address, unsigned long segment,
>  	if (!pmd_present(*pmd) &&
>  	    __pte_alloc(mm, vma, pmd, vmaddr))
>  		return -ENOMEM;
> +	/* large pmds cannot yet be handled */
> +	if (pmd_large(*pmd))
> +		return -EFAULT;

This bit wasn't in 8e72033f2a48.


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