Messages in this thread | | | Date | Tue, 23 Feb 2016 15:32:44 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH v3 1/2] mm: introduce page reference manipulation functions |
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On Tue, 23 Feb 2016 16:21:17 +0900 js1304@gmail.com wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@lge.com> > > 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.
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