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Date: Mon, 22 Nov 2010 14:14:49 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Minchan Kim <minchan.kim@...il.com>
Cc: linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
Peter Zijlstra <peterz@...radead.org>,
Rik van Riel <riel@...hat.com>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Johannes Weiner <hannes@...xchg.org>,
Nick Piggin <npiggin@...nel.dk>
Subject: Re: [RFC 1/2] deactive invalidated pages
On Sun, 21 Nov 2010 23:30:23 +0900
Minchan Kim <minchan.kim@...il.com> 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.
>
>
> ...
>
> +/*
> + * Function used to forecefully demote a page to the head of the inactive
> + * list.
> + */
This comment is wrong? The page gets moved to the _tail_ of the
inactive list?
> +void lru_deactive_page(struct page *page)
Should be "deactivate" throughout the patch. IMO.
> +{
> + 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);
This is the core part of the patch and it needs a code comment to
explain the reasons for doing this.
I wonder about the page_mapped() case. We were unable to invalidate
the page because it was mapped into pagetables. But was it really
appropriate to deactivate the page in that case?
> + count += ret;
> unlock_page(page);
> if (next > end)
> break;
Suggested updates:
include/linux/swap.h | 2 +-
mm/swap.c | 13 ++++++-------
mm/truncate.c | 7 ++++++-
3 files changed, 13 insertions(+), 9 deletions(-)
diff -puN include/linux/swap.h~mm-deactivate-invalidated-pages-fix include/linux/swap.h
--- a/include/linux/swap.h~mm-deactivate-invalidated-pages-fix
+++ a/include/linux/swap.h
@@ -213,7 +213,7 @@ extern void mark_page_accessed(struct pa
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 lru_deactivate_page(struct page *page);
extern void swap_setup(void);
extern void add_page_to_unevictable_list(struct page *page);
diff -puN mm/swap.c~mm-deactivate-invalidated-pages-fix mm/swap.c
--- a/mm/swap.c~mm-deactivate-invalidated-pages-fix
+++ a/mm/swap.c
@@ -39,7 +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_deactive_pvecs);
+static DEFINE_PER_CPU(struct pagevec, lru_deactivate_pvecs);
/*
@@ -334,23 +334,22 @@ static void drain_cpu_pagevecs(int cpu)
local_irq_restore(flags);
}
- pvec = &per_cpu(lru_deactive_pvecs, cpu);
+ pvec = &per_cpu(lru_deactivate_pvecs, cpu);
if (pagevec_count(pvec))
__pagevec_lru_deactive(pvec);
}
/*
- * Function used to forecefully demote a page to the head of the inactive
- * list.
+ * Forecfully demote a page to the tail of the inactive list.
*/
-void lru_deactive_page(struct page *page)
+void lru_deactivate_page(struct page *page)
{
if (likely(get_page_unless_zero(page))) {
- struct pagevec *pvec = &get_cpu_var(lru_deactive_pvecs);
+ struct pagevec *pvec = &get_cpu_var(lru_deactivate_pvecs);
if (!pagevec_add(pvec, page))
__pagevec_lru_deactive(pvec);
- put_cpu_var(lru_deactive_pvecs);
+ put_cpu_var(lru_deactivate_pvecs);
}
}
diff -puN mm/truncate.c~mm-deactivate-invalidated-pages-fix mm/truncate.c
--- a/mm/truncate.c~mm-deactivate-invalidated-pages-fix
+++ a/mm/truncate.c
@@ -361,8 +361,13 @@ unsigned long invalidate_mapping_pages(s
continue;
ret = invalidate_inode_page(page);
+ /*
+ * If the page was dirty or under writeback we cannot
+ * invalidate it now. Move it to the tail of the
+ * inactive LRU so that reclaim will free it promptly.
+ */
if (!ret)
- lru_deactive_page(page);
+ lru_deactivate_page(page);
count += ret;
unlock_page(page);
if (next > end)
_
--
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