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

[Andrew Morton <akpm@linux-foundation.org>]

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.

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