Re: [RFC 0/3] reduce latency of direct async compaction

[Aaron Lu]

On Tue, Dec 08, 2015 at 09:41:18AM +0900, Joonsoo Kim wrote:
> On Mon, Dec 07, 2015 at 04:59:56PM +0800, Aaron Lu wrote:
> > On Mon, Dec 07, 2015 at 04:35:24PM +0900, Joonsoo Kim wrote:
> > > It looks like overhead still remain. I guess that migration scanner
> > > would call pageblock_pfn_to_page() for more extended range so
> > > overhead still remain.
> > > 
> > > I have an idea to solve his problem. Aaron, could you test following patch
> > > on top of base? It tries to skip calling pageblock_pfn_to_page()
> > 
> > It doesn't apply on top of 25364a9e54fb8296837061bf684b76d20eec01fb
> > cleanly, so I made some changes to make it apply and the result is:
> > https://github.com/aaronlu/linux/commit/cb8d05829190b806ad3948ff9b9e08c8ba1daf63
> 
> Yes, that's okay. I made it on my working branch but it will not result in
> any problem except applying.
> 
> > 
> > There is a problem occured right after the test starts:
> > [   58.080962] BUG: unable to handle kernel paging request at ffffea0082000018
> > [   58.089124] IP: [<ffffffff81193f29>] compaction_alloc+0xf9/0x270
> > [   58.096109] PGD 107ffd6067 PUD 207f7d5067 PMD 0
> > [   58.101569] Oops: 0000 [#1] SMP 
> 
> I did some mistake. Please test following patch. It is also made
> on my working branch so you need to resolve conflict but it would be
> trivial.
> 
> I inserted some logs to check whether zone is contiguous or not.
> Please check that normal zone is set to contiguous after testing.

Yes it is contiguous, but unfortunately, the problem remains:
[   56.536930] check_zone_contiguous: Normal
[   56.543467] check_zone_contiguous: Normal: contiguous
[   56.549640] BUG: unable to handle kernel paging request at ffffea0082000018
[   56.557717] IP: [<ffffffff81193f29>] compaction_alloc+0xf9/0x270
[   56.564719] PGD 107ffd6067 PUD 207f7d5067 PMD 0

Full dmesg attached.

Thanks,
Aaron

> 
> Thanks.
> 
> ------>8------
> From 4a1a08d8ab3fb165b87ad2ec0a2000ff6892330f Mon Sep 17 00:00:00 2001
> From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> Date: Mon, 7 Dec 2015 14:51:42 +0900
> Subject: [PATCH] mm/compaction: Optimize pageblock_pfn_to_page() for
>  contiguous zone
> 
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> ---
>  include/linux/mmzone.h |  1 +
>  mm/compaction.c        | 54 +++++++++++++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 54 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index e23a9e7..573f9a9 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -521,6 +521,7 @@ struct zone {
>  #endif
>  
>  #if defined CONFIG_COMPACTION || defined CONFIG_CMA
> +       int                     contiguous;
>         /* Set to true when the PG_migrate_skip bits should be cleared */
>         bool                    compact_blockskip_flush;
>  #endif
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 67b8d90..cb5c7a2 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -88,7 +88,7 @@ static inline bool migrate_async_suitable(int migratetype)
>   * the first and last page of a pageblock and avoid checking each individual
>   * page in a pageblock.
>   */
> -static struct page *pageblock_pfn_to_page(unsigned long start_pfn,
> +static struct page *__pageblock_pfn_to_page(unsigned long start_pfn,
>                                 unsigned long end_pfn, struct zone *zone)
>  {
>         struct page *start_page;
> @@ -114,6 +114,56 @@ static struct page *pageblock_pfn_to_page(unsigned long start_pfn,
>         return start_page;
>  }
>  
> +static inline struct page *pageblock_pfn_to_page(unsigned long start_pfn,
> +                               unsigned long end_pfn, struct zone *zone)
> +{
> +       if (zone->contiguous == 1)
> +               return pfn_to_page(start_pfn);
> +
> +       return __pageblock_pfn_to_page(start_pfn, end_pfn, zone);
> +}
> +
> +static void check_zone_contiguous(struct zone *zone)
> +{
> +       unsigned long block_start_pfn = zone->zone_start_pfn;
> +       unsigned long block_end_pfn;
> +       unsigned long pfn;
> +
> +       /* Already checked */
> +       if (zone->contiguous)
> +               return;
> +
> +       printk("%s: %s\n", __func__, zone->name);
> +       block_end_pfn = ALIGN(block_start_pfn + 1, pageblock_nr_pages);
> +       for (; block_start_pfn < zone_end_pfn(zone);
> +               block_start_pfn = block_end_pfn,
> +               block_end_pfn += pageblock_nr_pages) {
> +
> +               block_end_pfn = min(block_end_pfn, zone_end_pfn(zone));
> +
> +               if (!__pageblock_pfn_to_page(block_start_pfn,
> +                                       block_end_pfn, zone)) {
> +                       /* We have hole */
> +                       zone->contiguous = -1;
> +                       printk("%s: %s: uncontiguous\n", __func__, zone->name);
> +                       return;
> +               }
> +
> +               /* Check validity of pfn within pageblock */
> +               for (pfn = block_start_pfn; pfn < block_end_pfn; pfn++) {
> +                       if (!pfn_valid_within(pfn)) {
> +                               zone->contiguous = -1;
> +                               printk("%s: %s: uncontiguous\n", __func__, zone->name);
> +                               return;
> +                       }
> +               }
> +       }
> +
> +       /* We don't have hole */
> +       zone->contiguous = 1;
> +       printk("%s: %s: contiguous\n", __func__, zone->name);
> +}
> +
>  #ifdef CONFIG_COMPACTION
>  
>  /* Do not skip compaction more than 64 times */
> @@ -1353,6 +1403,8 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
>                 ;
>         }
>  
> +       check_zone_contiguous(zone);
> +
>         /*
>          * Clear pageblock skip if there were failures recently and compaction
>          * is about to be retried after being deferred. kswapd does not do
> -- 
> 1.9.1
>

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