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    SubjectRe: [RFC 1/2] deactive invalidated pages
    On Sun, Nov 21, 2010 at 11:30:23PM +0900, Minchan Kim wrote:
    > 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 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)
    >
    > 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.
    >
    > 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@gmail.com>
    > Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
    > Signed-off-by: Peter Zijlstra <peterz@infradead.org>
    > Cc: Rik van Riel <riel@redhat.com>
    > Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    > Cc: Johannes Weiner <hannes@cmpxchg.org>
    > Cc: Nick Piggin <npiggin@kernel.dk>
    >
    > 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)
    > +{

    Might be worth commenting that this function must be called with pre-emption
    disabled. FWIW, I am reasonably sure your implementation is prefectly safe
    but a note wouldn't hurt.

    > + 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);
    > +

    What about memcg, do we not need to be calling mem_cgroup_add_lru_list() here
    as well? I'm looking at the differences between what move_active_pages_to_lru()
    is doing and this. I'm wondering if it'd be worth your whole building a list
    of active pages that are to be moved to the inactive list and passing them
    to move_active_pages_to_lru() ? I confuess I have not thought about it deeply
    so it might be a terrible suggestion but it might reduce duplication of code.

    > + update_page_reclaim_stat(zone, page, file, 0);
    > + }
    > + }
    > + }
    > + 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.

    s/forecefully/forcefully/

    The comment should also state *why* and under what circumstances we move
    pages to the inactive list like this. Also based on the discussions
    elsewhere in this thread, it'd be nice to include a comment why it's the
    head of the inactive list and not the tail.

    > + */
    > +void lru_deactive_page(struct page *page)
    > +{
    > + if (likely(get_page_unless_zero(page))) {
    > + 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);
    >

    --
    Mel Gorman
    Part-time Phd Student Linux Technology Center
    University of Limerick IBM Dublin Software Lab


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