On 25.06.19 09:52, Oscar Salvador wrote:
> Introduce a set of functions for Vmemmap pages.
> Set of functions:
>
> - {Set,Clear,Check} Vmemmap flag
> - Given a vmemmap page, get its vmemmap-head
> - Get #nr of vmemmap pages taking into account the current position
> of the page
>
> These functions will be used for the code handling Vmemmap pages.
>
> Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
> ---
> include/linux/page-flags.h | 34 ++++++++++++++++++++++++++++++++++
> mm/util.c | 2 ++
> 2 files changed, 36 insertions(+)
>
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index b848517da64c..a8b9b57162b3 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -466,6 +466,40 @@ static __always_inline int __PageMovable(struct page *page)
> PAGE_MAPPING_MOVABLE;
> }
>
> +#define VMEMMAP_PAGE (~PAGE_MAPPING_FLAGS)
> +static __always_inline int PageVmemmap(struct page *page)
> +{
> + return PageReserved(page) && (unsigned long)page->mapping == VMEMMAP_PAGE;
> +}
> +
> +static __always_inline int __PageVmemmap(struct page *page)
> +{
> + return (unsigned long)page->mapping == VMEMMAP_PAGE;
> +}
> +
> +static __always_inline void __ClearPageVmemmap(struct page *page)
> +{
Should we VM_BUG_ON in case !PG_reserved || pg->mapping != VMEMMAP_PAGE ?
> + __ClearPageReserved(page);
> + page->mapping = NULL;
> +}
> +
> +static __always_inline void __SetPageVmemmap(struct page *page)
> +{
Should we VM_BUG_ON in case PG_reserved || pg->mapping != NULL ?
> + __SetPageReserved(page);
> + page->mapping = (void *)VMEMMAP_PAGE;
> +}
> +
> +static __always_inline struct page *vmemmap_get_head(struct page *page)
> +{
> + return (struct page *)page->freelist;
freelist is a "slab, slob and slub" concept (reading
include/linux/mm_types.h). page->mapping is a "Page cache and anonymous
pages" concept. Hmmm...
> +}
> +
> +static __always_inline unsigned long get_nr_vmemmap_pages(struct page *page)
> +{
> + struct page *head = vmemmap_get_head(page);
> + return head->private - (page - head);
> +}
> +
> #ifdef CONFIG_KSM
> /*
> * A KSM page is one of those write-protected "shared pages" or "merged pages"
> diff --git a/mm/util.c b/mm/util.c
> index 021648a8a3a3..5e20563cdef6 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -607,6 +607,8 @@ struct address_space *page_mapping(struct page *page)
> mapping = page->mapping;
> if ((unsigned long)mapping & PAGE_MAPPING_ANON)
> return NULL;
> + if ((unsigned long)mapping == VMEMMAP_PAGE)
> + return NULL;
>
> return (void *)((unsigned long)mapping & ~PAGE_MAPPING_FLAGS);
> }
>
I wonder if using a page type would be appropriate here instead. Then,
define a new sub-structure within "struct page" that describes what you
actually want (instead of reusing ->private and ->mapping). Just an
idea, we have to find out if that is possible.
vmemmap_get_head() smells like __GFP_COMP, but of course, these vmemmap
pages never saw the buddy. But sounds like you want a similar concept.
--
Thanks,
David / dhildenb
