Re: [PATCH] mm/vmalloc: Fix regression caused by needless vmalloc_sync_all()

[Shile Zhang]

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@xxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxx/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@xxxxxxxxxxxxxxxxxxxx>
> Subject: mm-vmalloc-fix-regression-caused-by-needless-vmalloc_sync_all-fix
>
> simplify config expression, use IS_ENABLED()
>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: Joerg Roedel <jroedel@xxxxxxx>
> Cc: Qian Cai <cai@xxxxxx>
> Cc: Shile Zhang <shile.zhang@xxxxxxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
>
>   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
>   
>   	/*
> _