From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: akpm@linux-foundation.org, benh@kernel.crashing.org, paulus@samba.org,
        mpe@ellerman.id.au, linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 2/2] mm: THP page cache support for ppc64
In-Reply-To: <20161111101439.GB19382@node.shutemov.name>
References: <20161107083441.21901-1-aneesh.kumar@linux.vnet.ibm.com> <20161107083441.21901-2-aneesh.kumar@linux.vnet.ibm.com> <20161111101439.GB19382@node.shutemov.name>
Date: Fri, 11 Nov 2016 17:42:11 +0530
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Message-Id: <8737iy1ahw.fsf@linux.vnet.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
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"Kirill A. Shutemov" <kirill@shutemov.name> writes:

> On Mon, Nov 07, 2016 at 02:04:41PM +0530, Aneesh Kumar K.V wrote:
>> @@ -2953,6 +2966,13 @@ static int do_set_pmd(struct fault_env *fe, struct page *page)
>>  	ret = VM_FAULT_FALLBACK;
>>  	page = compound_head(page);
>>  
>> +	/*
>> +	 * Archs like ppc64 need additonal space to store information
>> +	 * related to pte entry. Use the preallocated table for that.
>> +	 */
>> +	if (arch_needs_pgtable_deposit() && !fe->prealloc_pte)
>> +		fe->prealloc_pte = pte_alloc_one(vma->vm_mm, fe->address);
>> +
>
> -ENOMEM handling?

How about

	if (arch_needs_pgtable_deposit() && !fe->prealloc_pte) {
		fe->prealloc_pte = pte_alloc_one(vma->vm_mm, fe->address);
		if (!fe->prealloc_pte)
			return VM_FAULT_OOM;
	}


>
> I think we should do this way before this point. Maybe in do_fault() or
> something.

doing this in do_set_pmd keeps this closer to where we set the pmd. Any
reason you thing we should move it higher up the stack. We already do
pte_alloc() at the same level for a non transhuge case in
alloc_set_pte().

-aneesh