Re: [PATCH] zsmalloc: zs_page_migrate: skip unnecessary loops but not return -EBUSY if zspage is not inuse

[Minchan Kim]

On Mon, Jul 24, 2017 at 05:45:35PM +0800, Hui Zhu wrote:
> The first version is in [1].
> 
> Got -EBUSY from zs_page_migrate will make migration
> slow (retry) or fail (zs_page_putback will schedule_work free_work,
> but it cannot ensure the success).
> 
> I noticed this issue because my Kernel patched [2]
> that will remove retry in __alloc_contig_migrate_range.
> This retry willhandle the -EBUSY because it will re-isolate the page
> and re-call migrate_pages.
> Without it will make cma_alloc fail at once with -EBUSY.
> 
> According to the review from Minchan Kim in [3], I update the patch
> to skip unnecessary loops but not return -EBUSY if zspage is not inuse.
> 
> Following is what I got with highalloc-performance in a vbox with 2
> cpu 1G memory 512 zram as swap.  And the swappiness is set to 100.
>                                    ori          ne
>                                   orig         new
> Minor Faults                  50805113    50830235
> Major Faults                     43918       56530
> Swap Ins                         42087       55680
> Swap Outs                        89718      104700
> Allocation stalls                    0           0
> DMA allocs                       57787       52364
> DMA32 allocs                  47964599    48043563
> Normal allocs                        0           0
> Movable allocs                       0           0
> Direct pages scanned             45493       23167
> Kswapd pages scanned           1565222     1725078
> Kswapd pages reclaimed         1342222     1503037
> Direct pages reclaimed           45615       25186
> Kswapd efficiency                  85%         87%
> Kswapd velocity               1897.101    1949.042
> Direct efficiency                 100%        108%
> Direct velocity                 55.139      26.175
> Percentage direct scans             2%          1%
> Zone normal velocity          1952.240    1975.217
> Zone dma32 velocity              0.000       0.000
> Zone dma velocity                0.000       0.000
> Page writes by reclaim       89764.000  105233.000
> Page writes file                    46         533
> Page writes anon                 89718      104700
> Page reclaim immediate           21457        3699
> Sector Reads                   3259688     3441368
> Sector Writes                  3667252     3754836
> Page rescued immediate               0           0
> Slabs scanned                  1042872     1160855
> Direct inode steals               8042       10089
> Kswapd inode steals              54295       29170
> Kswapd skipped wait                  0           0
> THP fault alloc                    175         154
> THP collapse alloc                 226         289
> THP splits                           0           0
> THP fault fallback                  11          14
> THP collapse fail                    3           2
> Compaction stalls                  536         646
> Compaction success                 322         358
> Compaction failures                214         288
> Page migrate success            119608      111063
> Page migrate failure              2723        2593
> Compaction pages isolated       250179      232652
> Compaction migrate scanned     9131832     9942306
> Compaction free scanned        2093272     2613998
> Compaction cost                    192         189
> NUMA alloc hit                47124555    47193990
> NUMA alloc miss                      0           0
> NUMA interleave hit                  0           0
> NUMA alloc local              47124555    47193990
> NUMA base PTE updates                0           0
> NUMA huge PMD updates                0           0
> NUMA page range updates              0           0
> NUMA hint faults                     0           0
> NUMA hint local faults               0           0
> NUMA hint local percent            100         100
> NUMA pages migrated                  0           0
> AutoNUMA cost                       0%          0%
> 
> [1]: https://lkml.org/lkml/2017/7/14/93
> [2]: https://lkml.org/lkml/2014/5/28/113
> [3]: https://lkml.org/lkml/2017/7/21/10
> 
> Signed-off-by: Hui Zhu <zhuhui@xxxxxxxxxx>
> ---
>  mm/zsmalloc.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index d41edd2..c2c7ba9 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1997,8 +1997,11 @@ int zs_page_migrate(struct address_space *mapping, struct page *newpage,
>  
>  	spin_lock(&class->lock);
>  	if (!get_zspage_inuse(zspage)) {
> -		ret = -EBUSY;
> -		goto unlock_class;
> +		/*
> +		 * Set "offset" to end of the page so that every loops
> +		 * skips unnecessary object scanning.
> +		 */
> +		offset = PAGE_SIZE;
>  	}
>  
>  	pos = offset;
> @@ -2066,7 +2069,7 @@ int zs_page_migrate(struct address_space *mapping, struct page *newpage,
>  		}
>  	}
>  	kunmap_atomic(s_addr);
> -unlock_class:
> +

Unncessary newline.

Other than that, Looks good to me.

Acked-by: Minchan Kim <minchan@xxxxxxxxxx>

Thanks!