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

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Date:   Tue, 16 Jan 2018 17:16:02 +0100
From:   Christophe LEROY <christophe.leroy@....fr>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        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



Le 16/01/2018 à 16:53, Aneesh Kumar K.V a écrit :
> 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.

We are in file asm/mmu-8xx.h so it obviously only applies to 8xx

Christophe

> 
> 
>>   	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