Re: [PATCH v3 17/25] mm: Add __page_cache_alloc_order

[Yang Shi]

On Wed, Apr 29, 2020 at 6:37 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
>
> This new function allows page cache pages to be allocated that are
> larger than an order-0 page.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> ---
>  include/linux/pagemap.h | 24 +++++++++++++++++++++---
>  mm/filemap.c            | 12 ++++++++----
>  2 files changed, 29 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 55199cb5bd66..1169e2428dd7 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -205,15 +205,33 @@ static inline int page_cache_add_speculative(struct page *page, int count)
>         return __page_cache_add_speculative(page, count);
>  }
>
> +static inline gfp_t thp_gfpmask(gfp_t gfp)
> +{
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +       /* We'd rather allocate smaller pages than stall a page fault */
> +       gfp |= GFP_TRANSHUGE_LIGHT;

This looks not correct. GFP_TRANSHUGE_LIGHT may set GFP_FS, but some
filesystem may expect GFP_NOFS, i.e. in readahead path.

> +       gfp &= ~__GFP_DIRECT_RECLAIM;
> +#endif
> +       return gfp;
> +}
> +
>  #ifdef CONFIG_NUMA
> -extern struct page *__page_cache_alloc(gfp_t gfp);
> +extern struct page *__page_cache_alloc_order(gfp_t gfp, unsigned int order);
>  #else
> -static inline struct page *__page_cache_alloc(gfp_t gfp)
> +static inline
> +struct page *__page_cache_alloc_order(gfp_t gfp, unsigned int order)
>  {
> -       return alloc_pages(gfp, 0);
> +       if (order == 0)
> +               return alloc_pages(gfp, 0);
> +       return prep_transhuge_page(alloc_pages(thp_gfpmask(gfp), order));
>  }
>  #endif
>
> +static inline struct page *__page_cache_alloc(gfp_t gfp)
> +{
> +       return __page_cache_alloc_order(gfp, 0);
> +}
> +
>  static inline struct page *page_cache_alloc(struct address_space *x)
>  {
>         return __page_cache_alloc(mapping_gfp_mask(x));
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 23a051a7ef0f..9abba062973a 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -941,24 +941,28 @@ int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
>  EXPORT_SYMBOL_GPL(add_to_page_cache_lru);
>
>  #ifdef CONFIG_NUMA
> -struct page *__page_cache_alloc(gfp_t gfp)
> +struct page *__page_cache_alloc_order(gfp_t gfp, unsigned int order)
>  {
>         int n;
>         struct page *page;
>
> +       if (order > 0)
> +               gfp = thp_gfpmask(gfp);
> +
>         if (cpuset_do_page_mem_spread()) {
>                 unsigned int cpuset_mems_cookie;
>                 do {
>                         cpuset_mems_cookie = read_mems_allowed_begin();
>                         n = cpuset_mem_spread_node();
> -                       page = __alloc_pages_node(n, gfp, 0);
> +                       page = __alloc_pages_node(n, gfp, order);
> +                       prep_transhuge_page(page);
>                 } while (!page && read_mems_allowed_retry(cpuset_mems_cookie));
>
>                 return page;
>         }
> -       return alloc_pages(gfp, 0);
> +       return prep_transhuge_page(alloc_pages(gfp, order));
>  }
> -EXPORT_SYMBOL(__page_cache_alloc);
> +EXPORT_SYMBOL(__page_cache_alloc_order);
>  #endif
>
>  /*
> --
> 2.26.2
>
>