From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [PATCH v3 1/2] mm: introduce page reference manipulation functions Date: Tue, 23 Feb 2016 15:32:44 -0800 Message-ID: <20160223153244.83a5c3ca430c4248a4a34cc0@linux-foundation.org> References: <1456212078-22732-1-git-send-email-iamjoonsoo.kim@lge.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1456212078-22732-1-git-send-email-iamjoonsoo.kim@lge.com> Sender: owner-linux-mm@kvack.org To: js1304@gmail.com Cc: Michal Nazarewicz , Minchan Kim , Mel Gorman , Vlastimil Babka , "Kirill A. Shutemov" , Sergey Senozhatsky , Steven Rostedt , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, Joonsoo Kim List-Id: linux-api@vger.kernel.org On Tue, 23 Feb 2016 16:21:17 +0900 js1304@gmail.com wrote: > From: Joonsoo Kim > > Success of CMA allocation largely depends on success of migration > and key factor of it is page reference count. Until now, page reference > is manipulated by direct calling atomic functions so we cannot follow up > who and where manipulate it. Then, it is hard to find actual reason > of CMA allocation failure. CMA allocation should be guaranteed to succeed > so finding offending place is really important. > > In this patch, call sites where page reference is manipulated are converted > to introduced wrapper function. This is preparation step to add tracepoint > to each page reference manipulation function. With this facility, we can > easily find reason of CMA allocation failure. There is no functional change > in this patch. > > ... > > --- a/arch/mips/mm/gup.c > +++ b/arch/mips/mm/gup.c > @@ -64,7 +64,7 @@ static inline void get_head_page_multiple(struct page *page, int nr) > { > VM_BUG_ON(page != compound_head(page)); > VM_BUG_ON(page_count(page) == 0); > - atomic_add(nr, &page->_count); > + page_ref_add(page, nr); Seems reasonable. Those open-coded refcount manipulations have always bugged me. The patches will be a bit of a pain to maintain but surprisingly they apply OK at present. It's possible that by the time they hit upstream, some direct ->_count references will still be present and it will require a second pass to complete the conversion. After that pass is completed I suggest we rename page._count to something else (page.ref_count_dont_use_this_directly_you_dope?). That way, any attempts to later add direct page._count references will hopefully break, alerting the programmer to the new regime. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org