linux-kernel - Re: [PATCH 1/2] mm: Avoid putting a bad page back on the LRU v7

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Message-Id: <200807221242.10552.nickpiggin@yahoo.com.au>
Date:	Tue, 22 Jul 2008 12:42:10 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Russ Anderson <rja@....com>
Cc:	mingo@...e.hu, tglx@...utronix.de, Tony Luck <tony.luck@...el.com>,
	linux-kernel@...r.kernel.org, linux-ia64@...r.kernel.org
Subject: Re: [PATCH 1/2] mm: Avoid putting a bad page back on the LRU v7

On Saturday 19 July 2008 06:36, Russ Anderson wrote:
> [PATCH 1/2] mm: Avoid putting a bad page back on the LRU v7
>
> Prevent a page with a physical memory error from being placed back
> on the LRU.  A new page flag (PG_memerror) is added if
> CONFIG_PAGEFLAGS_EXTENDED is defined.
>
> Signed-off-by: Russ Anderson <rja@....com>
> Reviewed-by: Christoph Lameter <clameter@....com>
>
> ---
>  include/linux/page-flags.h |   18 ++++++++++++++++--
>  mm/migrate.c               |   31 ++++++++++++++++++++++++++++++-
>  mm/page_alloc.c            |   13 ++++++++-----
>  3 files changed, 54 insertions(+), 8 deletions(-)
>
> Index: linux/mm/page_alloc.c
> ===================================================================
> --- linux.orig/mm/page_alloc.c	2008-07-18 15:15:48.000000000 -0500
> +++ linux/mm/page_alloc.c	2008-07-18 15:16:09.000000000 -0500
> @@ -602,10 +602,10 @@ static int prep_new_page(struct page *pa
>  		bad_page(page);
>
>  	/*
> -	 * For now, we report if PG_reserved was found set, but do not
> -	 * clear it, and do not allocate the page: as a safety net.
> +	 * For now, we report if PG_reserved or PG_memerror was found set, but
> +	 * do not clear it, and do not allocate the page: as a safety net.
>  	 */
> -	if (PageReserved(page))
> +	if (PageReserved(page) || PageMemError(page))
>  		return 1;
>
>  	page->flags &= ~(1 << PG_uptodate | 1 << PG_error | 1 << PG_reclaim |
> @@ -2475,8 +2475,11 @@ static void setup_zone_migrate_reserve(s
>  			continue;
>  		page = pfn_to_page(pfn);
>
> -		/* Blocks with reserved pages will never free, skip them. */
> -		if (PageReserved(page))
> +		/*
> +		 * Blocks with reserved pages or memory errors will never
> +		 * free, skip them.
> +		 */
> +		if (PageReserved(page) || PageMemError(page))
>  			continue;
>
>  		block_migratetype = get_pageblock_migratetype(page);

I don't like adding more branches like this into fastpaths like this. It
would make a lot more sense to me if you just had some private module that
does the job of isolating the page from the lru and/or elevating their
refcount so that they do not get put back on freelists.

Migration may need something to perhaps allow migrations of pages not on
LRU lists but have PageMemError set which is OK, but I really don't like
adding code and branches to page_alloc.c if possible....

Thanks,
Nick
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