Re: [PATCH] mm/page_alloc.c: drop dead destroy_compound_page()

["Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>]

Andrew Morton wrote:
> On Mon,  5 Jan 2015 13:46:22 +0200 "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> wrote:
> 
> > The only caller is __free_one_page(). By the time we should have
> > page->flags to be cleared already:
> > 
> >  - for 0-order pages though PCP list:
> > 	free_hot_cold_page()
> > 		free_pages_prepare()
> > 			free_pages_check()
> > 				page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
> > 		<put the page to PCP list>
> > 
> > 	free_pcppages_bulk()
> > 		page = <withdraw pages from PCP list>
> > 		__free_one_page(page)
> > 
> >  - for non-0-order pages:
> > 	__free_pages_ok()
> > 		free_pages_prepare()
> > 			free_pages_check()
> > 				page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
> > 		free_one_page()
> > 			__free_one_page()
> > 
> > So there's no way PageCompound() will return true in __free_one_page().
> > Let's remove dead destroy_compound_page() and put assert for page->flags
> > there instead.
> 
> Well.  An alternative would be to fix up the call site so those
> useful-looking checks actually get to check things.  Perhaps under
> CONFIG_DEBUG_VM.

Something like this?