add_to_page_cache_locked - add a locked page to the pagecache

int add_to_page_cache_locked(struct page *  page , struct address_space *  mapping , pgoff_t  offset , gfp_t  gfp_mask );

page
    page to add

mapping
    the pageAqs address_space

offset
    page index

gfp_mask
    page allocation mode

This function is used to add a page to the pagecache. It must be locked. This function does not add the page to the LRU. The caller must do that.