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

From: Minchan Kim
Date: Tue Jul 25 2017 - 03:26:56 EST


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!