linux-kernel - Re: [PATCH v3 2/8] mm/debug-pagealloc: prepare boottime configurable on/off

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Date:	Thu, 27 Nov 2014 13:35:39 +0100
From:	Paul Bolle <pebolle@...cali.nl>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	Valentin Rothberg <valentinrothberg@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan@...nel.org>, Dave Hansen <dave@...1.net>,
	Michal Nazarewicz <mina86@...a86.com>,
	Jungsoo Son <jungsoo.son@....com>,
	Ingo Molnar <mingo@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/8] mm/debug-pagealloc: prepare boottime
 configurable on/off

Joonsoo,

On Mon, 2014-11-24 at 17:15 +0900, Joonsoo Kim wrote:
> Until now, debug-pagealloc needs extra flags in struct page, so we need
> to recompile whole source code when we decide to use it. This is really
> painful, because it takes some time to recompile and sometimes rebuild is
> not possible due to third party module depending on struct page.
> So, we can't use this good feature in many cases.
> 
> Now, we have the page extension feature that allows us to insert
> extra flags to outside of struct page. This gets rid of third party module
> issue mentioned above. And, this allows us to determine if we need extra
> memory for this page extension in boottime. With these property, we can
> avoid using debug-pagealloc in boottime with low computational overhead
> in the kernel built with CONFIG_DEBUG_PAGEALLOC. This will help our
> development process greatly.
> 
> This patch is the preparation step to achive above goal. debug-pagealloc
> originally uses extra field of struct page, but, after this patch, it
> will use field of struct page_ext. Because memory for page_ext is
> allocated later than initialization of page allocator in CONFIG_SPARSEMEM,
> we should disable debug-pagealloc feature temporarily until initialization
> of page_ext. This patch implements this.
> 
> v2: fix compile error on CONFIG_PAGE_POISONING
> 
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>

This patch is included in today's linux-next (ie, next-2o0141127) as
commit 1e491e9be4c9 ("mm/debug-pagealloc: prepare boottime configurable
on/off").

> [...]
> 
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 33a8acf..c7b22e7 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -10,7 +10,6 @@
>  #include <linux/rwsem.h>
>  #include <linux/completion.h>
>  #include <linux/cpumask.h>
> -#include <linux/page-debug-flags.h>
>  #include <linux/uprobes.h>
>  #include <linux/page-flags-layout.h>
>  #include <asm/page.h>
> @@ -186,9 +185,6 @@ struct page {
>  	void *virtual;			/* Kernel virtual address (NULL if
>  					   not kmapped, ie. highmem) */
>  #endif /* WANT_PAGE_VIRTUAL */
> -#ifdef CONFIG_WANT_PAGE_DEBUG_FLAGS
> -	unsigned long debug_flags;	/* Use atomic bitops on this */
> -#endif
>  
>  #ifdef CONFIG_KMEMCHECK
>  	/*
> diff --git a/include/linux/page-debug-flags.h b/include/linux/page-debug-flags.h
> deleted file mode 100644
> index 22691f61..0000000
> --- a/include/linux/page-debug-flags.h
> +++ /dev/null
> @@ -1,32 +0,0 @@
> -#ifndef LINUX_PAGE_DEBUG_FLAGS_H
> -#define  LINUX_PAGE_DEBUG_FLAGS_H
> -
> -/*
> - * page->debug_flags bits:
> - *
> - * PAGE_DEBUG_FLAG_POISON is set for poisoned pages. This is used to
> - * implement generic debug pagealloc feature. The pages are filled with
> - * poison patterns and set this flag after free_pages(). The poisoned
> - * pages are verified whether the patterns are not corrupted and clear
> - * the flag before alloc_pages().
> - */
> -
> -enum page_debug_flags {
> -	PAGE_DEBUG_FLAG_POISON,		/* Page is poisoned */
> -	PAGE_DEBUG_FLAG_GUARD,
> -};
> -
> -/*
> - * Ensure that CONFIG_WANT_PAGE_DEBUG_FLAGS reliably
> - * gets turned off when no debug features are enabling it!
> - */
> -
> -#ifdef CONFIG_WANT_PAGE_DEBUG_FLAGS
> -#if !defined(CONFIG_PAGE_POISONING) && \
> -    !defined(CONFIG_PAGE_GUARD) \
> -/* && !defined(CONFIG_PAGE_DEBUG_SOMETHING_ELSE) && ... */
> -#error WANT_PAGE_DEBUG_FLAGS is turned on with no debug features!
> -#endif
> -#endif /* CONFIG_WANT_PAGE_DEBUG_FLAGS */
> -
> -#endif /* LINUX_PAGE_DEBUG_FLAGS_H */

This remove all uses of CONFIG_WANT_PAGE_DEBUG_FLAGS and
CONFIG_PAGE_GUARD. So the Kconfig symbols WANT_PAGE_DEBUG_FLAGS and
PAGE_GUARD are now unused.

Should I submit the trivial patch to remove these symbols or is a patch
that does that queued already?


Paul Bolle

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