From: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx> Rewrite this documentation to be more clear about the expectations for users. Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx> --- include/linux/page-flags.h | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index 393bb93b6b89..a6931046cc5c 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -164,24 +164,26 @@ static __always_inline struct page *CheckPageInit(struct page *page) } /* - * Page flags policies wrt compound pages + * Page flag policies describe how each page flag is used for compound pages. * * PF_ANY: - * the page flag is relevant for small, head and tail pages. + * This page flag is relevant for single, head and tail pages. * * PF_HEAD: - * for compound page all operations related to the page flag applied to - * head page. + * The head page contains the flag for the entire compound page. + * Callers may pass any subpage of the compound page, and the operation + * will be carried out on the head page. * * PF_ONLY_HEAD: - * for compound page, callers only ever operate on the head page. + * Callers only ever operate on the head page (or single pages). * * PF_TAIL_READ: - * modifications of the page flag must be done on small or head pages, - * checks can be done on tail pages too. + * The head page contains the flag for the entire compound page. + * If the flag is being modified, the caller must pass in the head page. + * For testing the flas, callers may use any subpage of the compound page. * * PF_NO_COMPOUND: - * the page flag is not relevant for compound pages. + * The page flag is not used for compound pages. */ #define PF_ANY(page, modify) CheckPageInit(page) #define PF_HEAD(page, modify) CheckPageInit(compound_head(page)) -- 2.16.3
