From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf1-f200.google.com (mail-pf1-f200.google.com [209.85.210.200]) by kanga.kvack.org (Postfix) with ESMTP id 994A96B02DA for ; Tue, 6 Nov 2018 03:47:51 -0500 (EST) Received: by mail-pf1-f200.google.com with SMTP id 190-v6so3461207pfd.7 for ; Tue, 06 Nov 2018 00:47:51 -0800 (PST) Received: from mga01.intel.com (mga01.intel.com. [192.55.52.88]) by mx.google.com with ESMTPS id z3-v6si45177065pgh.250.2018.11.06.00.47.50 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 06 Nov 2018 00:47:50 -0800 (PST) Date: Tue, 6 Nov 2018 16:47:46 +0800 From: Aaron Lu Subject: Re: [PATCH v2 2/2] mm/page_alloc: use a single function to free page Message-ID: <20181106084746.GA24198@intel.com> References: <20181105085820.6341-1-aaron.lu@intel.com> <20181105085820.6341-2-aaron.lu@intel.com> <20181106053037.GD6203@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Vlastimil Babka Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, Andrew Morton , =?utf-8?B?UGF3ZcWC?= Staszewski , Jesper Dangaard Brouer , Eric Dumazet , Tariq Toukan , Ilias Apalodimas , Yoel Caspersen , Mel Gorman , Saeed Mahameed , Michal Hocko , Dave Hansen , Alexander Duyck On Tue, Nov 06, 2018 at 09:16:20AM +0100, Vlastimil Babka wrote: > On 11/6/18 6:30 AM, Aaron Lu wrote: > > We have multiple places of freeing a page, most of them doing similar > > things and a common function can be used to reduce code duplicate. > > > > It also avoids bug fixed in one function but left in another. > > > > Signed-off-by: Aaron Lu > > Acked-by: Vlastimil Babka Thanks. > I assume there's no arch that would run page_ref_sub_and_test(1) slower > than put_page_testzero(), for the critical __free_pages() case? Good question. I followed the non-arch specific calls and found that: page_ref_sub_and_test() ends up calling atomic_sub_return(i, v) while put_page_testzero() ends up calling atomic_sub_return(1, v). So they should be same for archs that do not have their own implementations. Back to your question: I don't know either. If this is deemed unsafe, we can probably keep the ref modify part in their original functions and only take the free part into a common function. Regards, Aaron > > --- > > v2: move comments close to code as suggested by Dave. > > > > mm/page_alloc.c | 36 ++++++++++++++++-------------------- > > 1 file changed, 16 insertions(+), 20 deletions(-) > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 91a9a6af41a2..4faf6b7bf225 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -4425,9 +4425,17 @@ unsigned long get_zeroed_page(gfp_t gfp_mask) > > } > > EXPORT_SYMBOL(get_zeroed_page); > > > > -void __free_pages(struct page *page, unsigned int order) > > +static inline void free_the_page(struct page *page, unsigned int order, int nr) > > { > > - if (put_page_testzero(page)) { > > + VM_BUG_ON_PAGE(page_ref_count(page) == 0, page); > > + > > + /* > > + * Free a page by reducing its ref count by @nr. > > + * If its refcount reaches 0, then according to its order: > > + * order0: send to PCP; > > + * high order: directly send to Buddy. > > + */ > > + if (page_ref_sub_and_test(page, nr)) { > > if (order == 0) > > free_unref_page(page); > > else > > @@ -4435,6 +4443,10 @@ void __free_pages(struct page *page, unsigned int order) > > } > > } > > > > +void __free_pages(struct page *page, unsigned int order) > > +{ > > + free_the_page(page, order, 1); > > +} > > EXPORT_SYMBOL(__free_pages); > > > > void free_pages(unsigned long addr, unsigned int order) > > @@ -4481,16 +4493,7 @@ static struct page *__page_frag_cache_refill(struct page_frag_cache *nc, > > > > void __page_frag_cache_drain(struct page *page, unsigned int count) > > { > > - VM_BUG_ON_PAGE(page_ref_count(page) == 0, page); > > - > > - if (page_ref_sub_and_test(page, count)) { > > - unsigned int order = compound_order(page); > > - > > - if (order == 0) > > - free_unref_page(page); > > - else > > - __free_pages_ok(page, order); > > - } > > + free_the_page(page, compound_order(page), count); > > } > > EXPORT_SYMBOL(__page_frag_cache_drain); > > > > @@ -4555,14 +4558,7 @@ void page_frag_free(void *addr) > > { > > struct page *page = virt_to_head_page(addr); > > > > - if (unlikely(put_page_testzero(page))) { > > - unsigned int order = compound_order(page); > > - > > - if (order == 0) > > - free_unref_page(page); > > - else > > - __free_pages_ok(page, order); > > - } > > + free_the_page(page, compound_order(page), 1); > > } > > EXPORT_SYMBOL(page_frag_free); > > > > >