linux-kernel - Re: [PATCH 3/3] powerpc/8xx: Increase the number of mm slices

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Date:   Tue, 16 Jan 2018 21:23:32 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:     Christophe Leroy <christophe.leroy@....fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Scott Wood <oss@...error.net>,
        Nicholas Piggin <npiggin@...il.com>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 3/3] powerpc/8xx: Increase the number of mm slices

Christophe Leroy <christophe.leroy@....fr> writes:

> On the 8xx, we can have as many slices as PMD entries.
> This means we could have 1024 slices in 4k size pages mode
> and 64 slices in 16k size pages.
>
> However, due to a stack overflow in slice_get_unmapped_area(),
> we limit to 512 slices.
>
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> ---
>  arch/powerpc/include/asm/mmu-8xx.h | 6 +++++-
>  arch/powerpc/include/asm/page_32.h | 3 ++-
>  2 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/mmu-8xx.h b/arch/powerpc/include/asm/mmu-8xx.h
> index d669d0062da4..40aa7b0cd0dc 100644
> --- a/arch/powerpc/include/asm/mmu-8xx.h
> +++ b/arch/powerpc/include/asm/mmu-8xx.h
> @@ -171,7 +171,11 @@ typedef struct {
>  	unsigned long vdso_base;
>  #ifdef CONFIG_PPC_MM_SLICES
>  	u16 user_psize;		/* page size index */
> -	unsigned char low_slices_psize[8]; /* 16 slices */
> +#if defined(CONFIG_PPC_16K_PAGES)
> +	unsigned char low_slices_psize[32]; /* 64 slices */
> +#else
> +	unsigned char low_slices_psize[256]; /* 512 slices */
> +#endif

These #ifdef should be 8xx and then 16K.


>  	unsigned char high_slices_psize[0];
>  	unsigned long slb_addr_limit;
>  #endif
> diff --git a/arch/powerpc/include/asm/page_32.h b/arch/powerpc/include/asm/page_32.h
> index f7d1bd1183c8..43695ce7ee07 100644
> --- a/arch/powerpc/include/asm/page_32.h
> +++ b/arch/powerpc/include/asm/page_32.h
> @@ -62,7 +62,8 @@ extern void copy_page(void *to, void *from);
>  
>  #ifdef CONFIG_PPC_MM_SLICES
>  
> -#define SLICE_LOW_SHIFT		28
> +/* SLICE_LOW_SHIFT >= 23 to avoid stack overflow in slice_get_unmapped_area() */
> +#define SLICE_LOW_SHIFT		(PMD_SHIFT > 23 ? PMD_SHIFT : 23)
>  #define SLICE_HIGH_SHIFT	0
>  
>  #define SLICE_LOW_TOP		(0xfffffffful)
> -- 
> 2.13.3