Re: [PATCH v7] mm: Distinguish VMalloc pages

[Andrey Ryabinin <aryabinin@virtuozzo.com>]

On 07/10/2018 07:53 PM, Matthew Wilcox wrote:
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 21e1b6a9f113..8a4698b368de 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -153,6 +153,11 @@ struct page {
>  			spinlock_t ptl;
>  #endif
>  		};
> +		struct {	/* VMalloc pages */
> +			struct vm_struct *vm_area;
> +			unsigned long vm_offset;
> +			unsigned long _vm_id;	/* MAPPING_VMalloc */
> +		};
>  		struct {	/* ZONE_DEVICE pages */
>  			/** @pgmap: Points to the hosting device page map. */
>  			struct dev_pagemap *pgmap;
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 901943e4754b..588b8dd28a85 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -699,6 +699,32 @@ PAGE_TYPE_OPS(Kmemcg, kmemcg)
>   */
>  PAGE_TYPE_OPS(Table, table)
>  
> +/*
> + * vmalloc pages may be mapped to userspace, so we need some other way
> + * to distinguish them from other kinds of pages.  Use page->mapping for
> + * this purpose.  Values below 0x1000 cannot be real pointers.  Setting
> + * the bottom bit makes page_mapping() return NULL, which is what we want.
> + */
> +#define MAPPING_VMalloc		(void *)0x441

So this makes the vmalloc pages look like anon pages,
while previously they were !PageAnon.

I'm pretty sure this is not going to work.


> +
> +#define PAGE_MAPPING_OPS(name)						\
> +static __always_inline int Page##name(struct page *page)		\
> +{									\
> +	return page->mapping == MAPPING_##name;				\
> +}									\
> +static __always_inline void __SetPage##name(struct page *page)		\
> +{									\
> +	VM_BUG_ON_PAGE(page->mapping != NULL, page);			\
> +	page->mapping = MAPPING_##name;					\
> +}									\
> +static __always_inline void __ClearPage##name(struct page *page)	\
> +{									\
> +	VM_BUG_ON_PAGE(page->mapping != MAPPING_##name, page);		\
> +	page->mapping = NULL;						\
> +}
> +
> +PAGE_MAPPING_OPS(VMalloc)
> +