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

[Hiroyuki Kamezawa]

2011/2/18 Minchan Kim <minchan.kim@xxxxxxxxx>:
> On Fri, Feb 18, 2011 at 12:50 AM, KAMEZAWA Hiroyuki
> <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
>> On Fri, 18 Feb 2011 00:08:19 +0900
>> Minchan Kim <minchan.kim@xxxxxxxxx> 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 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@xxxxxxxxx>
>>> Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx>
>>> Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>>> Acked-by: Rik van Riel <riel@xxxxxxxxxx>
>>> Acked-by: Mel Gorman <mel@xxxxxxxxx>
>>> Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
>>> Cc: Wu Fengguang <fengguang.wu@xxxxxxxxx>
>>> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
>>> Cc: Nick Piggin <npiggin@xxxxxxxxx>
>>> Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx>
>>
>>
>> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
>>
>> One question is ....it seems there is no flush() code for percpu pagevec
>> in this patch. Is it safe against cpu hot plug ?
>>
>> And from memory hot unplug point of view, I'm grad if pagevec for this
>> is flushed at the same time as when we clear other per-cpu lru pagevecs.
>> (And compaction will be affected by the page_count() magic by pagevec
>>  which is flushed only when FADVISE is called.)
>>
>> Could you add add-on patches for flushing and hooks ?
>
> Isn't it enough in my patch? If I miss your point, Could you elaborate please?
>
>  * 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);
> +}
>

I'm sorry that I missed this line. It seems I was wrong.

Regards,
-Kame
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