On 05/11/2013 06:23 PM, Kirill A. Shutemov wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
>
> Returns true if mapping can have huge pages. Just check for __GFP_COMP
> in gfp mask of the mapping for now.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> ---
> include/linux/pagemap.h | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index e3dea75..28597ec 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -84,6 +84,18 @@ static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask)
> (__force unsigned long)mask;
> }
>
> +static inline bool mapping_can_have_hugepages(struct address_space *m)
> +{
> + if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE_PAGECACHE)) {
> + gfp_t gfp_mask = mapping_gfp_mask(m);
> + /* __GFP_COMP is key part of GFP_TRANSHUGE */
> + return !!(gfp_mask & __GFP_COMP) &&
> + transparent_hugepage_pagecache();
> + }
> +
> + return false;
> +}
transparent_hugepage_pagecache() already has the same IS_ENABLED()
check, Is it really necessary to do it again here?
IOW, can you do this?
> +static inline bool mapping_can_have_hugepages(struct address_space
> +{
> + gfp_t gfp_mask = mapping_gfp_mask(m);
if (!transparent_hugepage_pagecache())
return false;
> + /* __GFP_COMP is key part of GFP_TRANSHUGE */
> + return !!(gfp_mask & __GFP_COMP);
> +}
I know we talked about this in the past, but I've forgotten already.
Why is this checking for __GFP_COMP instead of GFP_TRANSHUGE?
Please flesh out the comment.
Also, what happens if "transparent_hugepage_flags &
(1<<TRANSPARENT_HUGEPAGE_PAGECACHE)" becomes false at runtime and you
have some already-instantiated huge page cache mappings around? Will
things like mapping_align_mask() break?
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