linux-kernel - Re: [PATCH] powerpc/mm: move warning from resize_hpt_for

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Message-ID: <20190308000923.GE7722@umbus.fritz.box>
Date:   Fri, 8 Mar 2019 11:09:23 +1100
From:   David Gibson <david@...son.dropbear.id.au>
To:     Laurent Vivier <lvivier@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Christophe Leroy <christophe.leroy@....fr>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] powerpc/mm: move warning from resize_hpt_for_hotplug()

On Thu, Mar 07, 2019 at 03:50:50PM +0100, Laurent Vivier wrote:
> resize_hpt_for_hotplug() reports a warning when it cannot
> resize the hash page table ("Unable to resize hash page
> table to target order") but in some cases it's not a problem
> and can make user thinks something has not worked properly.
> 
> This patch moves the warning to arch_remove_memory() to
> only report the problem when it is needed.
> 
> Signed-off-by: Laurent Vivier <lvivier@...hat.com>

Looks ok, but apart from the H_PTEG_FULL case this does allow for some
error paths that previously warned to pass without error, which I
don't think is wise.

Specifically that will happen the prepare hcall returns H_PARAMETER or
H_RESOURCE.  Thse will result in -EINVAL or -EPERM from
pseries_lpar_resize_hpt() which previously would have tripped the
warning in resize_hpt_for_hotplug() but now will be silently ignored.

> ---
>  arch/powerpc/include/asm/sparsemem.h  |  4 ++--
>  arch/powerpc/mm/hash_utils_64.c       | 17 ++++++-----------
>  arch/powerpc/mm/mem.c                 |  3 ++-
>  arch/powerpc/platforms/pseries/lpar.c |  1 -
>  4 files changed, 10 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/sparsemem.h b/arch/powerpc/include/asm/sparsemem.h
> index 68da49320592..3192d454a733 100644
> --- a/arch/powerpc/include/asm/sparsemem.h
> +++ b/arch/powerpc/include/asm/sparsemem.h
> @@ -17,9 +17,9 @@ extern int create_section_mapping(unsigned long start, unsigned long end, int ni
>  extern int remove_section_mapping(unsigned long start, unsigned long end);
>  
>  #ifdef CONFIG_PPC_BOOK3S_64
> -extern void resize_hpt_for_hotplug(unsigned long new_mem_size);
> +extern int resize_hpt_for_hotplug(unsigned long new_mem_size);
>  #else
> -static inline void resize_hpt_for_hotplug(unsigned long new_mem_size) { }
> +static inline int resize_hpt_for_hotplug(unsigned long new_mem_size) { return 0; }
>  #endif
>  
>  #ifdef CONFIG_NUMA
> diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
> index 0cc7fbc3bd1c..40bb2a8326bb 100644
> --- a/arch/powerpc/mm/hash_utils_64.c
> +++ b/arch/powerpc/mm/hash_utils_64.c
> @@ -755,12 +755,12 @@ static unsigned long __init htab_get_table_size(void)
>  }
>  
>  #ifdef CONFIG_MEMORY_HOTPLUG
> -void resize_hpt_for_hotplug(unsigned long new_mem_size)
> +int resize_hpt_for_hotplug(unsigned long new_mem_size)
>  {
>  	unsigned target_hpt_shift;
>  
>  	if (!mmu_hash_ops.resize_hpt)
> -		return;
> +		return 0;
>  
>  	target_hpt_shift = htab_shift_for_mem_size(new_mem_size);
>  
> @@ -773,15 +773,10 @@ void resize_hpt_for_hotplug(unsigned long new_mem_size)
>  	 * current shift
>  	 */
>  	if ((target_hpt_shift > ppc64_pft_size)
> -	    || (target_hpt_shift < (ppc64_pft_size - 1))) {
> -		int rc;
> -
> -		rc = mmu_hash_ops.resize_hpt(target_hpt_shift);
> -		if (rc && (rc != -ENODEV))
> -			printk(KERN_WARNING
> -			       "Unable to resize hash page table to target order %d: %d\n",
> -			       target_hpt_shift, rc);
> -	}
> +	    || (target_hpt_shift < (ppc64_pft_size - 1)))
> +		return mmu_hash_ops.resize_hpt(target_hpt_shift);
> +
> +	return 0;
>  }
>  
>  int hash__create_section_mapping(unsigned long start, unsigned long end, int nid)
> diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
> index 33cc6f676fa6..0d40d970cf4a 100644
> --- a/arch/powerpc/mm/mem.c
> +++ b/arch/powerpc/mm/mem.c
> @@ -169,7 +169,8 @@ int __meminit arch_remove_memory(int nid, u64 start, u64 size,
>  	 */
>  	vm_unmap_aliases();
>  
> -	resize_hpt_for_hotplug(memblock_phys_mem_size());
> +	if (resize_hpt_for_hotplug(memblock_phys_mem_size()) == -ENOSPC)
> +		pr_warn("Hash collision while resizing HPT\n");
>  
>  	return ret;
>  }
> diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
> index f2a9f0adc2d3..b407034a80ba 100644
> --- a/arch/powerpc/platforms/pseries/lpar.c
> +++ b/arch/powerpc/platforms/pseries/lpar.c
> @@ -918,7 +918,6 @@ static int pseries_lpar_resize_hpt(unsigned long shift)
>  	if (rc != 0) {
>  		switch (state.commit_rc) {
>  		case H_PTEG_FULL:
> -			pr_warn("Hash collision while resizing HPT\n");
>  			return -ENOSPC;
>  
>  		default:

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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