Hi Matthew,
On 5/5/2023 1:51 PM, Yin, Fengwei wrote:
> Hi Matthew,
>
> On 4/30/2023 6:35 AM, Matthew Wilcox wrote:
>> On Sat, Apr 29, 2023 at 04:27:59PM +0800, Yin Fengwei wrote:
>>> @@ -22,6 +23,7 @@ struct address_space;
>>> struct pagevec {
>>> unsigned char nr;
>>> bool percpu_pvec_drained;
>>> + unsigned short nr_pages;
>>
>> I still don't like storing nr_pages in the pagevec/folio_batch.
>>
>
> What about the change like following:
Soft ping.
Regards
Yin, Fengwei
>
> diff --git a/mm/swap.c b/mm/swap.c
> index 57cb01b042f6..5e7e9c0734ab 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -228,8 +228,10 @@ static void folio_batch_move_lru(struct folio_batch *fbatch, move_fn_t move_fn)
> static void folio_batch_add_and_move(struct folio_batch *fbatch,
> struct folio *folio, move_fn_t move_fn)
> {
> - if (folio_batch_add(fbatch, folio) && !folio_test_large(folio) &&
> - !lru_cache_disabled())
> + int nr_pages = folio_nr_pages(folio);
> +
> + if (folio_batch_add(fbatch, folio) && !lru_cache_disabled() &&
> + (!folio_test_large(folio) || (nr_pages <= (PAGEVEC_SIZE + 1))))
> return;
> folio_batch_move_lru(fbatch, move_fn);
> }
>
>
> I did testing about the lru lock contention with different folio size
> with will-it-scale + deferred queue lock contention mitigated:
> - If large folio size is 16K (order 2), the lru lock takes 64.31% cpu runtime
> - If large folio size is 64K (order 4), the lru lock takes 24.24% cpu runtime
> This is as our expectation: The larger size of folio, the less lru lock
> contention.
>
> It's acceptable to not batched operate on large folio which is large
> enough. PAGEVEC_SIZE + 1 is chosen here based on following reasons:
> - acceptable max memory size per batch: 15 x 16 x 4096 = 983040 bytes
> - the folios with size larger than it will not apply batched operation.
> But the lru lock contention is not high already.
>
>
> I collected data with lru contention when run will-it-scale.page_fault1:
>
> folio with order 2:
> Without the change:
> - 64.31% 0.23% page_fault1_pro [kernel.kallsyms] [k] folio_lruvec_lock_irqsave
> + 64.07% folio_lruvec_lock_irqsave
>
> With the change:
> - 21.55% 0.21% page_fault1_pro [kernel.kallsyms] [k] folio_lruvec_lock_irqsave
> + 21.34% folio_lruvec_lock_irqsave
>
> folio with order 4:
> Without the change:
> - 24.24% 0.15% page_fault1_pro [kernel.kallsyms] [k] folio_lruvec_lock_irqsave
> + 24.09% folio_lruvec_lock_irqsave
>
> With the change:
> - 2.20% 0.09% page_fault1_pro [kernel.kallsyms] [k] folio_lruvec_lock_irqsave
> + 2.11% folio_lruvec_lock_irqsave
>
> folio with order 5:
> - 8.21% 0.16% page_fault1_pro [kernel.kallsyms] [k] folio_lruvec_lock_irqsave
> + 8.05% folio_lruvec_lock_irqsave
>
>
> Regards
> Yin, Fengwei
>
