Re: [PATCH v5 1/4] deactivate invalidated pages

[Minchan Kim <minchan.kim@gmail.com>]

Hi Balbir,

On Fri, Feb 18, 2011 at 3:29 PM, Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> * MinChan Kim <minchan.kim@gmail.com> [2011-02-18 00:08:19]:
>
>> Recently, there are reported problem about thrashing.
>> (http://marc.info/?l=rsync&m=128885034930933&w=2)
>> It happens by backup workloads(ex, nightly rsync).
>> That's because the workload makes just use-once pages
>> and touches pages twice. It promotes the page into
>> active list so that it results in working set page eviction.
>>
>> Some app developer want to support POSIX_FADV_NOREUSE.
>> But other OSes don't support it, either.
>> (http://marc.info/?l=linux-mm&m=128928979512086&w=2)
>>
>> By other approach, app developers use POSIX_FADV_DONTNEED.
>> But it has a problem. If kernel meets page is writing
>> during invalidate_mapping_pages, it can't work.
>> It makes for application programmer to use it since 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)
>>
>> In fact, invalidation 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 if we can't truncate
>> it right now.
>>
>> Why I move page to head of lru on this patch, Dirty/Writeback page
>> would be flushed sooner or later. It can prevent writeout of pageout
>> which is less effective than flusher's writeout.
>>
>> Originally, I reused lru_demote of Peter with some change so added
>> his Signed-off-by.
>>
>> Reported-by: Ben Gamari <bgamari.foss@gmail.com>
>> Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
>> Signed-off-by: Peter Zijlstra <peterz@infradead.org>
>> Acked-by: Rik van Riel <riel@redhat.com>
>> Acked-by: Mel Gorman <mel@csn.ul.ie>
>> Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
>> Cc: Wu Fengguang <fengguang.wu@intel.com>
>> Cc: Johannes Weiner <hannes@cmpxchg.org>
>> Cc: Nick Piggin <npiggin@kernel.dk>
>> Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
>> ---
>> Changelog since v4:
>>  - Change function comments - suggested by Johannes
>>  - Change function name - suggested by Johannes
>>  - Drop only dirty/writeback pages to deactive pagevec - suggested by Johannes
>>  - Add acked-by
>>
>> Changelog since v3:
>>  - Change function comments - suggested by Johannes
>>  - Change function name - suggested by Johannes
>>  - add only dirty/writeback pages to deactive pagevec
>>
>> Changelog since v2:
>>  - mapped page leaves alone - suggested by Mel
>>  - pass part related PG_reclaim in next patch.
>>
>> Changelog since v1:
>>  - modify description
>>  - correct typo
>>  - add some comment
>>
>>  include/linux/swap.h |    1 +
>>  mm/swap.c            |   78 ++++++++++++++++++++++++++++++++++++++++++++++++++
>>  mm/truncate.c        |   17 ++++++++---
>>  3 files changed, 91 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/linux/swap.h b/include/linux/swap.h
>> index 4d55932..c335055 100644
>> --- a/include/linux/swap.h
>> +++ b/include/linux/swap.h
>> @@ -215,6 +215,7 @@ 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 deactivate_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 c02f936..4aea806 100644
>> --- a/mm/swap.c
>> +++ b/mm/swap.c
>> @@ -39,6 +39,7 @@ 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_deactivate_pvecs);
>>
>>  /*
>>   * This path almost never happens for VM activity - pages are normally
>> @@ -347,6 +348,60 @@ void add_page_to_unevictable_list(struct page *page)
>>  }
>>
>>  /*
>> + * If the page can not be invalidated, it is moved to the
>> + * inactive list to speed up its reclaim.  It is moved to the
>> + * head of the list, rather than the tail, to give the flusher
>> + * threads some time to write it out, as this is much more
>> + * effective than the single-page writeout from reclaim.
>> + */
>> +static void lru_deactivate(struct page *page, struct zone *zone)
>> +{
>> +     int lru, file;
>> +
>> +     if (!PageLRU(page) || !PageActive(page))
>> +             return;
>> +
>> +     /* Some processes are using the page */
>> +     if (page_mapped(page))
>> +             return;
>> +
>> +     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);
>> +}
>> +
>> +static void ____pagevec_lru_deactivate(struct pagevec *pvec)
>> +{
>> +     int i;
>> +     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);
>> +             }
>
> The optimization to avoid taking locks if the zone does not change is
> quite subtle

I just used it without big considering as it's a normal technique of
page array handling we have been used. So I want to keep it if it
doesn't make big overhead.

>
>> +             lru_deactivate(page, zone);
>> +     }
>> +     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
>>   * disabled; or "cpu" is being hot-unplugged, and is already dead.
>> @@ -372,6 +427,29 @@ static void drain_cpu_pagevecs(int cpu)
>>               pagevec_move_tail(pvec);
>>               local_irq_restore(flags);
>>       }
>> +
>> +     pvec = &per_cpu(lru_deactivate_pvecs, cpu);
>> +     if (pagevec_count(pvec))
>> +             ____pagevec_lru_deactivate(pvec);
>> +}
>> +
>> +/**
>> + * deactivate_page - forcefully deactivate a page
>> + * @page: page to deactivate
>> + *
>> + * This function hints the VM that @page is a good reclaim candidate,
>> + * for example if its invalidation fails due to the page being dirty
>> + * or under writeback.
>> + */
>> +void deactivate_page(struct page *page)
>> +{
>> +     if (likely(get_page_unless_zero(page))) {
>> +             struct pagevec *pvec = &get_cpu_var(lru_deactivate_pvecs);
>> +
>> +             if (!pagevec_add(pvec, page))
>> +                     ____pagevec_lru_deactivate(pvec);
>> +             put_cpu_var(lru_deactivate_pvecs);
>> +     }
>>  }
>>
>>  void lru_add_drain(void)
>> diff --git a/mm/truncate.c b/mm/truncate.c
>> index 4d415b3..9ec7bc5 100644
>> --- a/mm/truncate.c
>> +++ b/mm/truncate.c
>> @@ -328,11 +328,12 @@ EXPORT_SYMBOL(truncate_inode_pages);
>>   * pagetables.
>>   */
>>  unsigned long invalidate_mapping_pages(struct address_space *mapping,
>> -                                    pgoff_t start, pgoff_t end)
>> +             pgoff_t start, pgoff_t end)
>>  {
>>       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 +360,14 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping,
>>                       if (lock_failed)
>>                               continue;
>>
>> -                     ret += invalidate_inode_page(page);
>> -
>> +                     ret = invalidate_inode_page(page);
>> +                     /*
>> +                      * Invalidation is a hint that the page is no longer
>> +                      * of interest and try to speed up its reclaim.
>> +                      */
>> +                     if (!ret)
>> +                             deactivate_page(page);
>
> Do we need to do this under page_lock? Is there scope for us to reuse
> rotate_reclaimable_page() logic?

Good point.
I think we don't need page_lock. will fix.
About rotate_reclaimable_page, it has little bit similar logic but
several page flags test and irq disable are different so it would
result in ugly shape as far as I think.

I hope if you have a good idea, please, do refactoring after merging.

Thanks for the review, Balbir.

-- 
Kind regards,
Minchan Kim

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