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dkim=none (message not signed) header.d=none;kvack.org; dmarc=none action=none header.from=oracle.com; Received: from BYAPR10MB3077.namprd10.prod.outlook.com (2603:10b6:a03:8c::12) by BY5PR10MB3970.namprd10.prod.outlook.com (2603:10b6:a03:1ff::31) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3825.20; Thu, 4 Feb 2021 11:27:20 +0000 Received: from BYAPR10MB3077.namprd10.prod.outlook.com ([fe80::74a8:8649:e20b:d571]) by BYAPR10MB3077.namprd10.prod.outlook.com ([fe80::74a8:8649:e20b:d571%7]) with mapi id 15.20.3805.024; Thu, 4 Feb 2021 11:27:20 +0000 Subject: Re: [PATCH 1/4] mm/gup: add compound page list iterator To: John Hubbard Cc: linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org, Andrew Morton , Jason Gunthorpe , Doug Ledford , Matthew Wilcox , linux-mm@kvack.org References: <20210203220025.8568-1-joao.m.martins@oracle.com> <20210203220025.8568-2-joao.m.martins@oracle.com> <955dbe68-7302-a8bc-f0b5-e9032d7f190e@nvidia.com> From: Joao Martins Message-ID: Date: Thu, 4 Feb 2021 11:27:12 +0000 In-Reply-To: <955dbe68-7302-a8bc-f0b5-e9032d7f190e@nvidia.com> Content-Type: text/plain; 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It >> essentially counts the tails until the next page to process has a >> different head that the current. This is going to be used by >> unpin_user_pages() family of functions, to batch the head page refcount >> updates once for all passed consecutive tail pages. >> >> Suggested-by: Jason Gunthorpe >> Signed-off-by: Joao Martins >> --- >> mm/gup.c | 29 +++++++++++++++++++++++++++++ >> 1 file changed, 29 insertions(+) >> >> diff --git a/mm/gup.c b/mm/gup.c >> index d68bcb482b11..4f88dcef39f2 100644 >> --- a/mm/gup.c >> +++ b/mm/gup.c >> @@ -215,6 +215,35 @@ void unpin_user_page(struct page *page) >> } >> EXPORT_SYMBOL(unpin_user_page); >> >> +static inline unsigned int count_ntails(struct page **pages, unsigned long npages) > > Silly naming nit: could we please name this function count_pagetails()? count_ntails > is a bit redundant, plus slightly less clear. > Hmm, pagetails is also a tiny bit redundant. Perhaps count_subpages() instead? count_ntails is meant to be 'count number of tails' i.e. to align terminology with head + tails which was also suggested over the other series. >> +{ >> + struct page *head = compound_head(pages[0]); >> + unsigned int ntails; >> + >> + for (ntails = 1; ntails < npages; ntails++) { >> + if (compound_head(pages[ntails]) != head) >> + break; >> + } >> + >> + return ntails; >> +} >> + >> +static inline void compound_next(unsigned long i, unsigned long npages, >> + struct page **list, struct page **head, >> + unsigned int *ntails) >> +{ >> + if (i >= npages) >> + return; >> + >> + *ntails = count_ntails(list + i, npages - i); >> + *head = compound_head(list[i]); >> +} >> + >> +#define for_each_compound_head(i, list, npages, head, ntails) \ > > When using macros, which are dangerous in general, you have to worry about > things like name collisions. I really dislike that C has forced this unsafe > pattern upon us, but of course we are stuck with it, for iterator helpers. > /me nods > Given that we're stuck, you should probably use names such as __i, __list, etc, > in the the above #define. Otherwise you could stomp on existing variables. Will do. Joao