Re: [PATCH 2/2 v4]mm: batch activate_page() to reduce lock contention

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

On Tue, Mar 15, 2011 at 10:53 AM, Shaohua Li <shaohua.li@intel.com> wrote:
> On Mon, 2011-03-14 at 22:45 +0800, Minchan Kim wrote:
>> On Thu, Mar 10, 2011 at 01:30:19PM +0800, Shaohua Li wrote:
>> > The zone->lru_lock is heavily contented in workload where activate_page()
>> > is frequently used. We could do batch activate_page() to reduce the lock
>> > contention. The batched pages will be added into zone list when the pool
>> > is full or page reclaim is trying to drain them.
>> >
>> > For example, in a 4 socket 64 CPU system, create a sparse file and 64 processes,
>> > processes shared map to the file. Each process read access the whole file and
>> > then exit. The process exit will do unmap_vmas() and cause a lot of
>> > activate_page() call. In such workload, we saw about 58% total time reduction
>> > with below patch. Other workloads with a lot of activate_page also benefits a
>> > lot too.
>> >
>> > Andrew Morton suggested activate_page() and putback_lru_pages() should
>> > follow the same path to active pages, but this is hard to implement (see commit
>> > 7a608572a282a). On the other hand, do we really need putback_lru_pages() to
>> > follow the same path? I tested several FIO/FFSB benchmark (about 20 scripts for
>> > each benchmark) in 3 machines here from 2 sockets to 4 sockets. My test doesn't
>> > show anything significant with/without below patch (there is slight difference
>> > but mostly some noise which we found even without below patch before). Below
>> > patch basically returns to the same as my first post.
>> >
>> > I tested some microbenchmarks:
>> > case-anon-cow-rand-mt               0.58%
>> > case-anon-cow-rand          -3.30%
>> > case-anon-cow-seq-mt                -0.51%
>> > case-anon-cow-seq           -5.68%
>> > case-anon-r-rand-mt         0.23%
>> > case-anon-r-rand            0.81%
>> > case-anon-r-seq-mt          -0.71%
>> > case-anon-r-seq                     -1.99%
>> > case-anon-rx-rand-mt                2.11%
>> > case-anon-rx-seq-mt         3.46%
>> > case-anon-w-rand-mt         -0.03%
>> > case-anon-w-rand            -0.50%
>> > case-anon-w-seq-mt          -1.08%
>> > case-anon-w-seq                     -0.12%
>> > case-anon-wx-rand-mt                -5.02%
>> > case-anon-wx-seq-mt         -1.43%
>> > case-fork                   1.65%
>> > case-fork-sleep                     -0.07%
>> > case-fork-withmem           1.39%
>> > case-hugetlb                        -0.59%
>> > case-lru-file-mmap-read-mt  -0.54%
>> > case-lru-file-mmap-read             0.61%
>> > case-lru-file-mmap-read-rand        -2.24%
>> > case-lru-file-readonce              -0.64%
>> > case-lru-file-readtwice             -11.69%
>> > case-lru-memcg                      -1.35%
>> > case-mmap-pread-rand-mt             1.88%
>> > case-mmap-pread-rand                -15.26%
>> > case-mmap-pread-seq-mt              0.89%
>> > case-mmap-pread-seq         -69.72%
>> > case-mmap-xread-rand-mt             0.71%
>> > case-mmap-xread-seq-mt              0.38%
>> >
>> > The most significent are:
>> > case-lru-file-readtwice             -11.69%
>> > case-mmap-pread-rand                -15.26%
>> > case-mmap-pread-seq         -69.72%
>> >
>> > which use activate_page a lot.  others are basically variations because
>> > each run has slightly difference.
>> >
>> > In UP case, 'size mm/swap.o'
>> > before the two patches:
>> >    text    data     bss     dec     hex filename
>> >    6466     896       4    7366    1cc6 mm/swap.o
>> > after the two patches:
>> >    text    data     bss     dec     hex filename
>> >    6343     896       4    7243    1c4b mm/swap.o
>> >
>> > Signed-off-by: Shaohua Li <shaohua.li@intel.com>
>> >
>> > ---
>> >  mm/swap.c |   45 ++++++++++++++++++++++++++++++++++++++++-----
>> >  1 file changed, 40 insertions(+), 5 deletions(-)
>> >
>> > Index: linux/mm/swap.c
>> > ===================================================================
>> > --- linux.orig/mm/swap.c    2011-03-09 12:56:09.000000000 +0800
>> > +++ linux/mm/swap.c 2011-03-09 12:56:46.000000000 +0800
>> > @@ -272,14 +272,10 @@ static void update_page_reclaim_stat(str
>> >             memcg_reclaim_stat->recent_rotated[file]++;
>> >  }
>> >
>> > -/*
>> > - * FIXME: speed this up?
>> > - */
>> > -void activate_page(struct page *page)
>> > +static void __activate_page(struct page *page, void *arg)
>> >  {
>> >     struct zone *zone = page_zone(page);
>> >
>> > -   spin_lock_irq(&zone->lru_lock);
>> >     if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
>> >             int file = page_is_file_cache(page);
>> >             int lru = page_lru_base_type(page);
>> > @@ -292,8 +288,45 @@ void activate_page(struct page *page)
>> >
>> >             update_page_reclaim_stat(zone, page, file, 1);
>> >     }
>> > +}
>> > +
>> > +#ifdef CONFIG_SMP
>> > +static DEFINE_PER_CPU(struct pagevec, activate_page_pvecs);
>> > +
>> > +static void activate_page_drain(int cpu)
>> > +{
>> > +   struct pagevec *pvec = &per_cpu(activate_page_pvecs, cpu);
>> > +
>> > +   if (pagevec_count(pvec))
>> > +           pagevec_lru_move_fn(pvec, __activate_page, NULL);
>> > +}
>> > +
>> > +void activate_page(struct page *page)
>> > +{
>> > +   if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
>> > +           struct pagevec *pvec = &get_cpu_var(activate_page_pvecs);
>> > +
>> > +           page_cache_get(page);
>> > +           if (!pagevec_add(pvec, page))
>> > +                   pagevec_lru_move_fn(pvec, __activate_page, NULL);
>> > +           put_cpu_var(activate_page_pvecs);
>> > +   }
>> > +}
>> > +
>> > +#else
>> > +static inline void activate_page_drain(int cpu)
>> > +{
>> > +}
>> > +
>> > +void activate_page(struct page *page)
>> > +{
>> > +   struct zone *zone = page_zone(page);
>> > +
>> > +   spin_lock_irq(&zone->lru_lock);
>> > +   __activate_page(page, NULL);
>> >     spin_unlock_irq(&zone->lru_lock);
>> >  }
>> > +#endif
>>
>> Why do we need CONFIG_SMP in only activate_page_pvecs?
>> The per-cpu of activate_page_pvecs consumes lots of memory in UP?
>> I don't think so. But if it consumes lots of memory, it's a problem
>> of per-cpu.
> No, not too much memory.
>
>> I can't understand why we should hanlde activate_page_pvecs specially.
>> Please, enlighten me.
> Not it's special. akpm asked me to do it this time. Reducing little
> memory is still worthy anyway, so that's it. We can do it for other
> pvecs too, in separate patch.

Understandable but I don't like code separation by CONFIG_SMP for just
little bit enhance of memory usage. In future, whenever we use percpu,
do we have to implement each functions for both SMP and non-SMP?
Is it desirable?
Andrew, Is it really valuable?

If everybody agree, I don't oppose such way.
But now I vote code cleanness than reduce memory footprint.

>
> Thanks,
> Shaohua
>
>



-- 
Kind regards,
Minchan Kim

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