Re: [PATCH v3 5/6] powerpc/mm: Reduce memory usage for mm_context_t for radix

[Christophe Leroy <christophe.leroy@c-s.fr>]

Le 17/04/2019 à 15:03, Aneesh Kumar K.V a écrit :
> Currently, our mm_context_t on book3s64 include all hash specific
> context details like slice mask and subpage protection details. We
> can skip allocating these with radix translation. This will help us to save
> 8K per mm_context with radix translation.
> 
> With the patch applied we have
> 
> sizeof(mm_context_t)  = 136
> sizeof(struct hash_mm_context)  = 8288
> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> ---
>   arch/powerpc/include/asm/book3s/64/mmu-hash.h | 33 ++++++++++++-
>   arch/powerpc/include/asm/book3s/64/mmu.h      | 49 +++++--------------
>   arch/powerpc/kernel/setup-common.c            |  6 +++
>   arch/powerpc/mm/hash_utils_64.c               |  4 +-
>   arch/powerpc/mm/mmu_context_book3s64.c        | 16 +++++-
>   5 files changed, 68 insertions(+), 40 deletions(-)
> 

[...]

> diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setup-common.c
> index a07de8608484..21b1ce200b22 100644
> --- a/arch/powerpc/kernel/setup-common.c
> +++ b/arch/powerpc/kernel/setup-common.c
> @@ -947,6 +947,12 @@ void __init setup_arch(char **cmdline_p)
>   	init_mm.end_data = (unsigned long) _edata;
>   	init_mm.brk = klimit;
>   
> +#ifdef CONFIG_PPC_MM_SLICES
> +#if defined(CONFIG_PPC_8xx)
> +	init_mm.context.slb_addr_limit = DEFAULT_MAP_WINDOW;
> +#endif
> +#endif
> +

In the previous patch, you moved the above into early_init_mmu(). Why 
bringing it back here ?

Christophe

>   #ifdef CONFIG_SPAPR_TCE_IOMMU
>   	mm_iommu_init(&init_mm);
>   #endif
> diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
> index 2cb3a456f5b5..04ac7c36d380 100644
> --- a/arch/powerpc/mm/hash_utils_64.c
> +++ b/arch/powerpc/mm/hash_utils_64.c
> @@ -968,6 +968,7 @@ void __init hash__early_init_devtree(void)
>   	htab_scan_page_sizes();
>   }
>   
> +struct hash_mm_context init_hash_mm_context;
>   void __init hash__early_init_mmu(void)
>   {
>   #ifndef CONFIG_PPC_64K_PAGES
> @@ -1041,7 +1042,8 @@ void __init hash__early_init_mmu(void)
>   	 */
>   	htab_initialize();
>   
> -	init_mm.context.slb_addr_limit = DEFAULT_MAP_WINDOW_USER64;
> +	init_mm.context.hash_context = &init_hash_mm_context;
> +	init_mm.context.hash_context->slb_addr_limit = DEFAULT_MAP_WINDOW_USER64;
>   
>   	pr_info("Initializing hash mmu with SLB\n");
>   	/* Initialize SLB management */
> diff --git a/arch/powerpc/mm/mmu_context_book3s64.c b/arch/powerpc/mm/mmu_context_book3s64.c
> index f720c5cc0b5e..6eef5a36b2e9 100644
> --- a/arch/powerpc/mm/mmu_context_book3s64.c
> +++ b/arch/powerpc/mm/mmu_context_book3s64.c
> @@ -63,6 +63,12 @@ static int hash__init_new_context(struct mm_struct *mm)
>   	if (index < 0)
>   		return index;
>   
> +	mm->context.hash_context = kmalloc(sizeof(struct hash_mm_context), GFP_KERNEL);
> +	if (!mm->context.hash_context) {
> +		ida_free(&mmu_context_ida, index);
> +		return -ENOMEM;
> +	}
> +
>   	/*
>   	 * The old code would re-promote on fork, we don't do that when using
>   	 * slices as it could cause problem promoting slices that have been
> @@ -77,8 +83,14 @@ static int hash__init_new_context(struct mm_struct *mm)
>   	 * We should not be calling init_new_context() on init_mm. Hence a
>   	 * check against 0 is OK.
>   	 */
> -	if (mm->context.id == 0)
> +	if (mm->context.id == 0) {
> +		memset(mm->context.hash_context, 0, sizeof(struct hash_mm_context));
>   		slice_init_new_context_exec(mm);
> +	} else {
> +		/* This is fork. Copy hash_context details from current->mm */
> +		memcpy(mm->context.hash_context, current->mm->context.hash_context, sizeof(struct hash_mm_context));
> +
> +	}
>   
>   	subpage_prot_init_new_context(mm);
>   
> @@ -118,6 +130,7 @@ static int radix__init_new_context(struct mm_struct *mm)
>   	asm volatile("ptesync;isync" : : : "memory");
>   
>   	mm->context.npu_context = NULL;
> +	mm->context.hash_context = NULL;
>   
>   	return index;
>   }
> @@ -162,6 +175,7 @@ static void destroy_contexts(mm_context_t *ctx)
>   		if (context_id)
>   			ida_free(&mmu_context_ida, context_id);
>   	}
> +	kfree(ctx->hash_context);
>   }
>   
>   static void pmd_frag_destroy(void *pmd_frag)
>