Re: [PATCH 1/3] mm: Add __page_cache_alloc_order

From: Song Liu <songliubraving@fb.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Linux MM <linux-mm@kvack.org>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	Kirill Shutemov <kirill@shutemov.name>,
	William Kucharski <william.kucharski@oracle.com>,
	Johannes Weiner <jweiner@fb.com>
Subject: Re: [PATCH 1/3] mm: Add __page_cache_alloc_order
Date: Thu, 5 Sep 2019 18:58:53 +0000	[thread overview]
Message-ID: <75104154-A1A4-4FE3-920C-0069E1B5848D@fb.com> (raw)
In-Reply-To: <20190905182348.5319-2-willy@infradead.org>

> On Sep 5, 2019, at 11:23 AM, Matthew Wilcox <willy@infradead.org> wrote:
> 
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> 
> 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@infradead.org>
> ---
> include/linux/pagemap.h | 14 +++++++++++---
> mm/filemap.c            | 11 +++++++----
> 2 files changed, 18 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 103205494ea0..d2147215d415 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -208,14 +208,22 @@ static inline int page_cache_add_speculative(struct page *page, int count)
> }
> 
> #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);

I guess we need __page_cache_alloc(gfp_t gfp) here for CONFIG_NUMA. 

> #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)
> +		gfp |= __GFP_COMP;
> +	return alloc_pages(gfp, order);
> }
> #endif
> 
> +static inline struct page *__page_cache_alloc(gfp_t gfp)
> +{
> +	return __page_cache_alloc_order(gfp, 0);

Maybe "return alloc_pages(gfp, 0);" here to avoid checking "order > 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 05a5aa82cd32..041c77c4ca56 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -957,24 +957,27 @@ 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 |= __GFP_COMP;
> +

I think it will be good to have separate __page_cache_alloc() for order 0, 
so that we avoid checking "order > 0", but that may require too much 
duplication. So I am on the fence for this one. 

Thanks,
Song

> 	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);
> 		} while (!page && read_mems_allowed_retry(cpuset_mems_cookie));
> 
> 		return page;
> 	}
> -	return alloc_pages(gfp, 0);
> +	return alloc_pages(gfp, order);
> }
> -EXPORT_SYMBOL(__page_cache_alloc);
> +EXPORT_SYMBOL(__page_cache_alloc_order);
> #endif
> 
> /*
> -- 
> 2.23.0.rc1
> 