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Message-ID: <AANLkTikUq60GmqaUNSB8ipxG-+ezu8PYrdokAuAWQs1s@mail.gmail.com>
Date: Tue, 30 Nov 2010 15:18:41 +0900
From: Minchan Kim <minchan.kim@...il.com>
To: Johannes Weiner <hannes@...xchg.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-mm <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>,
Ben Gamari <bgamari.foss@...il.com>,
Peter Zijlstra <peterz@...radead.org>,
Wu Fengguang <fengguang.wu@...el.com>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Nick Piggin <npiggin@...nel.dk>, Mel Gorman <mel@....ul.ie>
Subject: Re: [PATCH v3 1/3] deactivate invalidated pages
Hi Hannes,
On Tue, Nov 30, 2010 at 2:22 PM, Johannes Weiner <hannes@...xchg.org> wrote:
> On Tue, Nov 30, 2010 at 12:23:19AM +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 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 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, 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.
>>
>> Why I need the page to head, 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@...il.com>
>> Signed-off-by: Minchan Kim <minchan.kim@...il.com>
>> Signed-off-by: Peter Zijlstra <peterz@...radead.org>
>> Acked-by: Rik van Riel <riel@...hat.com>
>> Cc: Wu Fengguang <fengguang.wu@...el.com>
>> Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
>> Cc: Johannes Weiner <hannes@...xchg.org>
>> Cc: Nick Piggin <npiggin@...nel.dk>
>> Cc: Mel Gorman <mel@....ul.ie>
>>
>> Adnrew. Before applying this series, please drop below two patches.
>> mm-deactivate-invalidated-pages.patch
>> mm-deactivate-invalidated-pages-fix.patch
>>
>> 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 | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++
>> mm/truncate.c | 16 +++++++--
>> 3 files changed, 93 insertions(+), 4 deletions(-)
>>
>> diff --git a/include/linux/swap.h b/include/linux/swap.h
>> index eba53e7..84375e4 100644
>> --- a/include/linux/swap.h
>> +++ b/include/linux/swap.h
>
> [...]
>
>> @@ -267,6 +270,63 @@ void add_page_to_unevictable_list(struct page *page)
>> }
>>
>> /*
>> + * This function is used by invalidate_mapping_pages.
>> + * If the page can't be invalidated, this function moves the page
>> + * into inative list's head. Because the VM expects the page would
>> + * be writeout by flusher. The flusher's writeout is much effective
>> + * than reclaimer's random writeout.
>
> The wording is a bit confusing, I find. It sounds a bit like the
> flusher's chance is increased by moving it to the inactive list in the
> first place, but the key is that it is moved to the head instead of,
> what one would expect, the tail of the list. How about:
>
> 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.
>
Looks good to me.
I will add your comment instead of my ugly comment.
>> +static void __lru_deactivate(struct page *page, struct zone *zone)
>
> Do you insist on the underscores? :)
Good point.
__lru_deactivate is self-contained.
It is valuable enough using other places.
I will remove underscores.
>
>> +{
>> + int lru, file;
>> + unsigned long vm_flags;
>> +
>> + 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);
>> +}
>> +
>> +/*
>> + * This function must be called with preemption disable.
>
> Why is that? Unless I missed something, the only thing that needs
> protection is the per-cpu pagevec reference the only user of this
> function passes in. But this should be the caller's concern and is
> not really a requirement of this function per-se, is it?
Yes. It's unnecessary.
I didn't consider enoughly.
Will fix.
>
>> +static void __pagevec_lru_deactivate(struct pagevec *pvec)
>
> More underscores!
Will fix.
>
>> +{
>> + 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);
>> + }
>> + __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.
>> @@ -292,6 +352,26 @@ 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);
>> +}
>> +
>> +/*
>> + * Forcefully deactivate a page.
>> + * This function is used for reclaiming the page ASAP when the page
>> + * can't be invalidated by Dirty/Writeback.
>
> How about:
>
> /**
> * lru_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 lru_deactivate_page(struct page *page)
>
> I would love that lru_ prefix for most of the API in this file. In
> fact, the file should probably be called lru.c. But for now, can you
> keep the naming consistent and call it deactivate_page?
No matter. I can change it. but deactivate_page will be asymmetric
about that deactivate_page move active page into inactive
forcefully(two step) while activate_page does one step activation.
That's why I name it.
>
>> + 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)
>
> [...]
>
>> @@ -359,8 +360,15 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping,
>> if (lock_failed)
>> continue;
>>
>> - ret += invalidate_inode_page(page);
>> -
>> + ret = invalidate_inode_page(page);
>> + /*
>> + * If the page was dirty or under writeback we cannot
>> + * invalidate it now. Move it to the head of the
>> + * inactive LRU for using deferred writeback of flusher.
>
> This would also be less confusing if it would say
>
> Move it to the head of the inactive LRU (rather than the tail)
> for using [...]
>
> But I am not sure that this detail is interesting at this point. It
> would be more interesting to name the reasons for why the page is
> moved to the inactive list in the first place:
>
> If the page is dirty or under writeback, we can not invalidate
> it now. But we assume that attempted invalidation is a hint
> that the page is no longer of interest and try to speed up its
> reclaim.
>
Will fix.
I hope listen you guys's opinions about [2/3], too. :)
Thanks, Hannes.
>> + */
>> + if (!ret)
>> + lru_deactivate_page(page);
>> + count += ret;
>> unlock_page(page);
>> if (next > end)
>> break;
>
> Hannes
>
--
Kind regards,
Minchan Kim
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