Re: error at compaction (Re: mmotm 2010-04-15-14-42 uploaded

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Mon, 19 Apr 2010 20:39:19 +0100
Mel Gorman <mel@csn.ul.ie> wrote:

> On Mon, Apr 19, 2010 at 07:14:42PM +0100, Mel Gorman wrote:
> > On Mon, Apr 19, 2010 at 07:01:33PM +0900, KAMEZAWA Hiroyuki wrote:
> > > 
> > > mmotm 2010-04-15-14-42 
> > > 
> > > When I tried 
> > >  # echo 0 > /proc/sys/vm/compaction
> > > 
> > > I see following.
> > > 
> > > My enviroment was 
> > >   2.6.34-rc4-mm1+ (2010-04-15-14-42) (x86-64) CPUx8
> > >   allocating tons of hugepages and reduce free memory.
> > > 
> > > What I did was:
> > >   # echo 0 > /proc/sys/vm/compact_memory
> > > 
> > > Hmm, I see this kind of error at migation for the 1st time..
> > > my.config is attached. Hmm... ?
> > > 
> > > (I'm sorry I'll be offline soon.)
> > 
> > That's ok, thanks you for the report. I'm afraid I made little progress
> > as I spent most of the day on other bugs but I do have something for
> > you.
> > 
> > First, I reproduced the problem using your .config. However, the problem does
> > not manifest with the .config I normally use which is derived from the distro
> > kernel configuration (Debian Lenny). So, there is something in your .config
> > that triggers the problem. I very strongly suspect this is an interaction
> > between migration, compaction and page allocation debug.
> 
> I unexpecedly had the time to dig into this. Does the following patch fix
> your problem? It Worked For Me.
> 
Ok, works for me, too.

Tested-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Thank you.
-Kame
> ==== CUT HERE ====
> mm,compaction: Map free pages in the address space after they get split for compaction
> 
> split_free_page() is a helper function which takes a free page from the
> buddy lists and splits it into order-0 pages. It is used by memory
> compaction to build a list of destination pages. If
> CONFIG_DEBUG_PAGEALLOC is set, a kernel paging request bug is triggered
> because split_free_page() did not call the arch-allocation hooks or map
> the page into the kernel address space.
> 
> This patch does not update split_free_page() as it is called with
> interrupts held. Instead it documents that callers of split_free_page()
> are responsible for calling the arch hooks and to map the page and fixes
> compaction.
> 
> This is a fix to the patch mm-compaction-memory-compaction-core.patch.
> 
> Signed-off-by: Mel Gorman <mel@csn.ul.ie>
> ---
>  mm/compaction.c |    6 ++++++
>  mm/page_alloc.c |    3 +++
>  2 files changed, 9 insertions(+), 0 deletions(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 8f4c518..6218e03 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -184,6 +184,12 @@ static void isolate_freepages(struct zone *zone,
>  	}
>  	spin_unlock_irqrestore(&zone->lock, flags);
>  
> +	/* split_free_page does not map the pages */
> +	list_for_each_entry(page, freelist, lru) {
> +		arch_alloc_page(page, 0);
> +		kernel_map_pages(page, 1, 1);
> +	}
> +
>  	cc->free_pfn = high_pfn;
>  	cc->nr_freepages = nr_freepages;
>  }
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 53442fd..b2af4d9 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1211,6 +1211,9 @@ void split_page(struct page *page, unsigned int order)
>  /*
>   * Similar to split_page except the page is already free. As this is only
>   * being used for migration, the migratetype of the block also changes.
> + * As this is called with interrupts disabled, the caller is responsible
> + * for calling arch_alloc_page() and kernel_map_page() after interrupts
> + * are enabled.
>   */
>  int split_free_page(struct page *page)
>  {
> --
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