linux-kernel - Re: [PATCH] mm/vmalloc: Fix regression caused by needless vmalloc_sync

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Date:   Thu, 14 Nov 2019 08:54:21 +0800
From:   Shile Zhang <shile.zhang@...ux.alibaba.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Joerg Roedel <jroedel@...e.de>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...el.com>, Qian Cai <cai@....pw>
Subject: Re: [PATCH] mm/vmalloc: Fix regression caused by needless
 vmalloc_sync_all()

Fix wrong cc list.

On 2019/11/14 05:12, Andrew Morton wrote:
> On Wed, 13 Nov 2019 17:55:30 +0800 Shile Zhang <shile.zhang@...ux.alibaba.com> wrote:
>
>> vmalloc_sync_all() was put in the common path in
>> __purge_vmap_area_lazy(), for one sync issue only happened on X86_32
>> with PTI enabled. It is needless for X86_64, which caused a big regression
>> in UnixBench Shell8 testing on X86_64.
>> Similar regression also reported by 0-day kernel test robot in reaim
>> benchmarking:
>> https://lists.01.org/hyperkitty/list/lkp@lists.01.org/thread/4D3JPPHBNOSPFK2KEPC6KGKS6J25AIDB/
> That is indeed a large performance regression.
>
>> Fix it by adding more conditions.
>>
>> Fixes: 3f8fd02b1bf1 ("mm/vmalloc: Sync unmappings in __purge_vmap_area_lazy()")
>>
>> ...
>>
>> --- a/mm/vmalloc.c
>> +++ b/mm/vmalloc.c
>> @@ -1255,11 +1255,17 @@ static bool __purge_vmap_area_lazy(unsigned long start, unsigned long end)
>>   	if (unlikely(valist == NULL))
>>   		return false;
>>   
>> +#if defined(CONFIG_X86_32) && defined(CONFIG_X86_PAE)
> Are we sure that x86_32 is the only architecture whcih is (or ever will
> be) affected?
>
>>   	/*
>>   	 * First make sure the mappings are removed from all page-tables
>>   	 * before they are freed.
>> +	 *
>> +	 * This is only needed on x86-32 with !SHARED_KERNEL_PMD, which is
>> +	 * the case on a PAE kernel with PTI enabled.
>>   	 */
>> -	vmalloc_sync_all();
>> +	if (!SHARED_KERNEL_PMD && boot_cpu_has(X86_FEATURE_PTI))
>> +		vmalloc_sync_all();
>> +#endif
>>   
>>   	/*
>>   	 * TODO: to calculate a flush range without looping.
> CONFIG_X86_PAE depends on CONFIG_X86_32 so no need to check
> CONFIG_X86_32?

Yes, Thanks for your review and kindly refactoring!

> From: Andrew Morton <akpm@...ux-foundation.org>
> Subject: mm-vmalloc-fix-regression-caused-by-needless-vmalloc_sync_all-fix
>
> simplify config expression, use IS_ENABLED()
>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Joerg Roedel <jroedel@...e.de>
> Cc: Qian Cai <cai@....pw>
> Cc: Shile Zhang <shile.zhang@...ux.alibaba.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> ---
>
>   mm/vmalloc.c |   21 +++++++++++----------
>   1 file changed, 11 insertions(+), 10 deletions(-)
>
> --- a/mm/vmalloc.c~mm-vmalloc-fix-regression-caused-by-needless-vmalloc_sync_all-fix
> +++ a/mm/vmalloc.c
> @@ -1255,16 +1255,17 @@ static bool __purge_vmap_area_lazy(unsig
>   	if (unlikely(valist == NULL))
>   		return false;
>   
> -#if defined(CONFIG_X86_32) && defined(CONFIG_X86_PAE)
> -	/*
> -	 * First make sure the mappings are removed from all page-tables
> -	 * before they are freed.
> -	 *
> -	 * This is only needed on x86-32 with !SHARED_KERNEL_PMD, which is
> -	 * the case on a PAE kernel with PTI enabled.
> -	 */
> -	if (!SHARED_KERNEL_PMD && boot_cpu_has(X86_FEATURE_PTI))
> -		vmalloc_sync_all();
> +	if (IS_ENABLED(CONFIG_X86_PAE)) {
> +		/*
> +		 * First make sure the mappings are removed from all page-tables
> +		 * before they are freed.
> +		 *
> +		 * This is only needed on x86-32 with !SHARED_KERNEL_PMD, which
> +		 * is the case on a PAE kernel with PTI enabled.
> +		 */
> +		if (!SHARED_KERNEL_PMD && boot_cpu_has(X86_FEATURE_PTI))
> +			vmalloc_sync_all();
> +	}
>   #endif
>   
>   	/*
> _