Subject: Re: [PATCH V2 09/29] powerpc/mm: Hugetlbfs is book3s_64 and fsl_book3e (32 or 64)

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Tue, 16 Feb 2016 13:50:05 +0530

Paul Mackerras <[email-masked]> writes:

> On Mon, Feb 08, 2016 at 02:50:21PM +0530, Aneesh Kumar K.V wrote:
>> We move large part of fsl related code to hugetlbpage-book3e.c.
>> Only code movement. This also avoid #ifdef in the code.
>> 
>> Signed-off-by: Aneesh Kumar K.V <[email-masked]>
>
> I am wondering why you are adding #ifdef CONFIG_PPC_FSL_BOOK3E
> instances to hugetlbpage-book3e.c.  As far as I can tell from the
> Kconfig* files, we only support hugetlbfs on book3s_64 and
> fsl_book3e.  Yet it seems like we have provision for 64-bit processors
> that are neither book3s_64 nor fsl_book3e.
>
> So it seems that in this existing code:

Correct. That confused me as well. Now I am moving nonhash code as it is
to avoid any regression there. We can take it up as a cleanup if those
#ifdef can be removed. With the current Kconfig setup, that will be dead
code. 

>
>> -static int __hugepte_alloc(struct mm_struct *mm, hugepd_t *hpdp,
>> -			   unsigned long address, unsigned pdshift, unsigned pshift)
>> -{
>> -	struct kmem_cache *cachep;
>> -	pte_t *new;
>> -
>> -#ifdef CONFIG_PPC_FSL_BOOK3E
>> -	int i;
>> -	int num_hugepd = 1 << (pshift - pdshift);
>> -	cachep = hugepte_cache;
>> -#else
>> -	cachep = PGT_CACHE(pdshift - pshift);
>> -#endif
>> -
>> -	new = kmem_cache_zalloc(cachep, GFP_KERNEL|__GFP_REPEAT);
>> -
>> -	BUG_ON(pshift > HUGEPD_SHIFT_MASK);
>> -	BUG_ON((unsigned long)new & HUGEPD_SHIFT_MASK);
>> -
>> -	if (! new)
>> -		return -ENOMEM;
>> -
>> -	spin_lock(&mm->page_table_lock);
>> -#ifdef CONFIG_PPC_FSL_BOOK3E
>> -	/*
>> -	 * We have multiple higher-level entries that point to the same
>> -	 * actual pte location.  Fill in each as we go and backtrack on error.
>> -	 * We need all of these so the DTLB pgtable walk code can find the
>> -	 * right higher-level entry without knowing if it's a hugepage or not.
>> -	 */
>> -	for (i = 0; i < num_hugepd; i++, hpdp++) {
>> -		if (unlikely(!hugepd_none(*hpdp)))
>> -			break;
>> -		else
>> -			/* We use the old format for PPC_FSL_BOOK3E */
>> -			hpdp->pd = ((unsigned long)new & ~PD_HUGE) | pshift;
>> -	}
>> -	/* If we bailed from the for loop early, an error occurred, clean up */
>> -	if (i < num_hugepd) {
>> -		for (i = i - 1 ; i >= 0; i--, hpdp--)
>> -			hpdp->pd = 0;
>> -		kmem_cache_free(cachep, new);
>> -	}
>> -#else
>> -	if (!hugepd_none(*hpdp))
>> -		kmem_cache_free(cachep, new);
>> -	else {
>> -#ifdef CONFIG_PPC_BOOK3S_64
>> -		hpdp->pd = (unsigned long)new |
>> -			    (shift_to_mmu_psize(pshift) << 2);
>> -#else
>> -		hpdp->pd = ((unsigned long)new & ~PD_HUGE) | pshift;
>
> this last line here hasn't ended up anywhere and has effectively been
> deleted.  Was that deliberate?
>

Didn't get that . We do that in nonhash __hpte_alloc. Adding that here
for easy review.

	spin_lock(&mm->page_table_lock);
	/*
	 * We have multiple higher-level entries that point to the same
	 * actual pte location.  Fill in each as we go and backtrack on error.
	 * We need all of these so the DTLB pgtable walk code can find the
	 * right higher-level entry without knowing if it's a hugepage or not.
	 */
	for (i = 0; i < num_hugepd; i++, hpdp++) {
		if (unlikely(!hugepd_none(*hpdp)))
			break;
		else
			/* We use the old format for PPC_FSL_BOOK3E */
			hpdp->pd = ((unsigned long)new & ~PD_HUGE) | pshift;
	}

and the book3s 64 bit variant

	spin_lock(&mm->page_table_lock);
	if (!hugepd_none(*hpdp))
		kmem_cache_free(cachep, new);
	else {
		hpdp->pd = (unsigned long)new |
			    (shift_to_mmu_psize(pshift) << 2);
	}

-aneesh