From: Nicholas Piggin <npiggin@gmail.com>
To: Christophe Leroy <christophe.leroy@c-s.fr>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org,
aneesh.kumar@linux.vnet.ibm.com,
Michael Ellerman <mpe@ellerman.id.au>,
linuxppc-dev@lists.ozlabs.org,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: How to handle PTE tables with non contiguous entries ?
Date: Tue, 11 Sep 2018 07:06:45 +1000 [thread overview]
Message-ID: <20180911070645.239aef8a@roar.ozlabs.ibm.com> (raw)
In-Reply-To: <ddc3bb56-4da0-c093-256f-185d4a612b5c@c-s.fr>
On Mon, 10 Sep 2018 14:34:37 +0000
Christophe Leroy <christophe.leroy@c-s.fr> wrote:
> Hi,
>
> I'm having a hard time figuring out the best way to handle the following
> situation:
>
> On the powerpc8xx, handling 16k size pages requires to have page tables
> with 4 identical entries.
>
> Initially I was thinking about handling this by simply modifying
> pte_index() which changing pte_t type in order to have one entry every
> 16 bytes, then replicate the PTE value at *ptep, *ptep+1,*ptep+2 and
> *ptep+3 both in set_pte_at() and pte_update().
>
> However, this doesn't work because many many places in the mm core part
> of the kernel use loops on ptep with single ptep++ increment.
>
> Therefore did it with the following hack:
>
> /* PTE level */
> +#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PPC_16K_PAGES)
> +typedef struct { pte_basic_t pte, pte1, pte2, pte3; } pte_t;
> +#else
> typedef struct { pte_basic_t pte; } pte_t;
> +#endif
>
> @@ -181,7 +192,13 @@ static inline unsigned long pte_update(pte_t *p,
> : "cc" );
> #else /* PTE_ATOMIC_UPDATES */
> unsigned long old = pte_val(*p);
> - *p = __pte((old & ~clr) | set);
> + unsigned long new = (old & ~clr) | set;
> +
> +#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PPC_16K_PAGES)
> + p->pte = p->pte1 = p->pte2 = p->pte3 = new;
> +#else
> + *p = __pte(new);
> +#endif
> #endif /* !PTE_ATOMIC_UPDATES */
>
> #ifdef CONFIG_44x
>
>
> @@ -161,7 +161,11 @@ static inline void __set_pte_at(struct mm_struct
> *mm, unsigned long addr,
> /* Anything else just stores the PTE normally. That covers all
> 64-bit
> * cases, and 32-bit non-hash with 32-bit PTEs.
> */
> +#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PPC_16K_PAGES)
> + ptep->pte = ptep->pte1 = ptep->pte2 = ptep->pte3 = pte_val(pte);
> +#else
> *ptep = pte;
> +#endif
>
>
>
> But I'm not too happy with it as it means pte_t is not a single type
> anymore so passing it from one function to the other is quite heavy.
>
>
> Would someone have an idea of an elegent way to handle that ?
I can't think of anything better. Do we pass pte by value to a lot of
non inlined functions? Possible to inline the important ones?
Other option, try to get an iterator like pte = pte_next(pte) into core
code.
Thanks,
Nick
next prev parent reply other threads:[~2018-09-10 21:06 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-10 14:34 How to handle PTE tables with non contiguous entries ? Christophe Leroy
2018-09-10 20:05 ` Dan Malek
2018-09-11 5:28 ` Christophe LEROY
2018-09-10 21:06 ` Nicholas Piggin [this message]
2018-09-11 5:39 ` Christophe LEROY
2018-09-17 9:03 ` Aneesh Kumar K.V
2018-09-17 9:47 ` Christophe LEROY
2018-09-18 11:47 ` Aneesh Kumar K.V
2018-09-18 11:53 ` Christophe LEROY
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