linux-kernel - Re: [PATCH 2/2] mm: THP page cache support for ppc64

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Date:   Fri, 11 Nov 2016 17:42:11 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     akpm@...ux-foundation.org, benh@...nel.crashing.org,
        paulus@...ba.org, mpe@...erman.id.au, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 2/2] mm: THP page cache support for ppc64

"Kirill A. Shutemov" <kirill@...temov.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