Re: [RFC 1/2] deactive invalidated pages

[Minchan Kim]

Hi KOSAKI,

2010/11/23 KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>:
>> By Other approach, app developer uses POSIX_FADV_DONTNEED.
>> But it has a problem. If kernel meets page is writing
>> during invalidate_mapping_pages, it can't work.
>> It is very hard for application programmer to use it.
>> Because they always have to sync data before calling
>> fadivse(..POSIX_FADV_DONTNEED) to make sure the pages could
>> be discardable. At last, they can't use deferred write of kernel
>> so that they could see performance loss.
>> (http://insights.oetiker.ch/linux/fadvise.html)
>
> If rsync use the above url patch, we don't need your patch.
> fdatasync() + POSIX_FADV_DONTNEED should work fine.

It works well. But it needs always fdatasync before calling fadvise.
For small file, it hurt performance since we can't use the deferred write.

>
> So, I think the core worth of previous PeterZ's patch is in readahead
> based heuristics. I'm curious why you drop it.
>

In previous peter's patch, it couldn't move active page into inactive list.
So it's not what i want and I think invalidation is stronger hint than
the readahead heuristic.
But if we need it, I will add it in my series. It can help reclaiming
unnecessary inactive page asap.
but before that, I hope we make sure fadvise works well enough.

>
>> In fact, invalidate is very big hint to reclaimer.
>> It means we don't use the page any more. So let's move
>> the writing page into inactive list's head.
>
> But, I agree this.

Thank you.

>
>
>>
>> If it is real working set, it could have a enough time to
>> activate the page since we always try to keep many pages in
>> inactive list.
>>
>> I reuse lru_demote of Peter with some change.
>>
>> Reported-by: Ben Gamari <bgamari.foss@xxxxxxxxx>
>> Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx>
>> Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>> Cc: Rik van Riel <riel@xxxxxxxxxx>
>> Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
>> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
>> Cc: Nick Piggin <npiggin@xxxxxxxxx>
>>
>> Ben, Remain thing is to modify rsync and use
>> fadvise(POSIX_FADV_DONTNEED). Could you test it?
>> ---
>>  include/linux/swap.h |    1 +
>>  mm/swap.c            |   61 ++++++++++++++++++++++++++++++++++++++++++++++++++
>>  mm/truncate.c        |   11 +++++---
>>  3 files changed, 69 insertions(+), 4 deletions(-)
>>
>> diff --git a/include/linux/swap.h b/include/linux/swap.h
>> index eba53e7..a3c9248 100644
>> --- a/include/linux/swap.h
>> +++ b/include/linux/swap.h
>> @@ -213,6 +213,7 @@ extern void mark_page_accessed(struct page *);
>>  extern void lru_add_drain(void);
>>  extern int lru_add_drain_all(void);
>>  extern void rotate_reclaimable_page(struct page *page);
>> +extern void lru_deactive_page(struct page *page);
>>  extern void swap_setup(void);
>>
>>  extern void add_page_to_unevictable_list(struct page *page);
>> diff --git a/mm/swap.c b/mm/swap.c
>> index 3f48542..56fa298 100644
>> --- a/mm/swap.c
>> +++ b/mm/swap.c
>> @@ -39,6 +39,8 @@ int page_cluster;
>>
>>  static DEFINE_PER_CPU(struct pagevec[NR_LRU_LISTS], lru_add_pvecs);
>>  static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs);
>> +static DEFINE_PER_CPU(struct pagevec, lru_deactive_pvecs);
>> +
>>
>>  /*
>>   * This path almost never happens for VM activity - pages are normally
>> @@ -266,6 +268,45 @@ void add_page_to_unevictable_list(struct page *page)
>>       spin_unlock_irq(&zone->lru_lock);
>>  }
>>
>> +static void __pagevec_lru_deactive(struct pagevec *pvec)
>> +{
>> +     int i, lru, file;
>> +
>> +     struct zone *zone = NULL;
>> +
>> +     for (i = 0; i < pagevec_count(pvec); i++) {
>> +             struct page *page = pvec->pages[i];
>> +             struct zone *pagezone = page_zone(page);
>> +
>> +             if (pagezone != zone) {
>> +                     if (zone)
>> +                             spin_unlock_irq(&zone->lru_lock);
>> +                     zone = pagezone;
>> +                     spin_lock_irq(&zone->lru_lock);
>> +             }
>> +
>> +             if (PageLRU(page)) {
>> +                     if (PageActive(page)) {
>> +                             file = page_is_file_cache(page);
>> +                             lru = page_lru_base_type(page);
>> +                             del_page_from_lru_list(zone, page,
>> +                                             lru + LRU_ACTIVE);
>> +                             ClearPageActive(page);
>> +                             ClearPageReferenced(page);
>> +                             add_page_to_lru_list(zone, page, lru);
>> +                             __count_vm_event(PGDEACTIVATE);
>> +
>> +                             update_page_reclaim_stat(zone, page, file, 0);
>
> When PageActive is unset, we need to change cgroup lru too.

Doesn't add_page_to_lru_list/del_page_from_lru_list do it?

>
>
>> +                     }
>> +             }
>> +     }
>> +     if (zone)
>> +             spin_unlock_irq(&zone->lru_lock);
>> +
>> +     release_pages(pvec->pages, pvec->nr, pvec->cold);
>> +     pagevec_reinit(pvec);
>> +}
>> +
>>  /*
>>   * Drain pages out of the cpu's pagevecs.
>>   * Either "cpu" is the current CPU, and preemption has already been
>> @@ -292,8 +333,28 @@ static void drain_cpu_pagevecs(int cpu)
>>               pagevec_move_tail(pvec);
>>               local_irq_restore(flags);
>>       }
>> +
>> +     pvec = &per_cpu(lru_deactive_pvecs, cpu);
>> +     if (pagevec_count(pvec))
>> +             __pagevec_lru_deactive(pvec);
>> +}
>> +
>> +/*
>> + * Function used to forecefully demote a page to the head of the inactive
>> + * list.
>> + */
>> +void lru_deactive_page(struct page *page)
>> +{
>> +     if (likely(get_page_unless_zero(page))) {
>
> Probably, we can check PageLRU and PageActive here too. It help to avoid
> unnecessary batching and may slightly increase performance.

Yes. Thanks. Will fix.

>
>
>> +             struct pagevec *pvec = &get_cpu_var(lru_deactive_pvecs);
>> +
>> +             if (!pagevec_add(pvec, page))
>> +                     __pagevec_lru_deactive(pvec);
>> +             put_cpu_var(lru_deactive_pvecs);
>> +     }
>>  }
>>
>> +
>>  void lru_add_drain(void)
>>  {
>>       drain_cpu_pagevecs(get_cpu());
>> diff --git a/mm/truncate.c b/mm/truncate.c
>> index cd94607..c73fb19 100644
>> --- a/mm/truncate.c
>> +++ b/mm/truncate.c
>> @@ -332,7 +332,8 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping,
>>  {
>>       struct pagevec pvec;
>>       pgoff_t next = start;
>> -     unsigned long ret = 0;
>> +     unsigned long ret;
>> +     unsigned long count = 0;
>>       int i;
>>
>>       pagevec_init(&pvec, 0);
>> @@ -359,8 +360,10 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping,
>>                       if (lock_failed)
>>                               continue;
>>
>> -                     ret += invalidate_inode_page(page);
>> -
>> +                     ret = invalidate_inode_page(page);
>> +                     if (!ret)
>> +                             lru_deactive_page(page);
>> +                     count += ret;
>>                       unlock_page(page);
>>                       if (next > end)
>>                               break;
>> @@ -369,7 +372,7 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping,
>>               mem_cgroup_uncharge_end();
>>               cond_resched();
>>       }
>> -     return ret;
>> +     return count;
>>  }
>>  EXPORT_SYMBOL(invalidate_mapping_pages);
>>
>> --
>> 1.7.0.4
>>
>> --
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>
>
>
>



-- 
Kind regards,
Minchan Kim
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