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Message-ID: <20130121015222.GA3666@blaptop>
Date: Mon, 21 Jan 2013 10:52:22 +0900
From: Minchan Kim <minchan@...nel.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
Dan Magenheimer <dan.magenheimer@...cle.com>,
Sonny Rao <sonnyrao@...gle.com>,
Bryan Freed <bfreed@...gle.com>,
Hugh Dickins <hughd@...gle.com>,
Rik van Riel <riel@...hat.com>,
Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH 1/2] mm: prevent to add a page to swap if may_writepage
is unset
Hi,
On Fri, Jan 18, 2013 at 08:36:42AM +0900, Minchan Kim wrote:
> On Thu, Jan 17, 2013 at 02:22:38PM -0800, Andrew Morton wrote:
> > On Thu, 17 Jan 2013 09:53:14 +0900
> > Minchan Kim <minchan@...nel.org> wrote:
> >
> > > Recently, Luigi reported there are lots of free swap space when
> > > OOM happens. It's easily reproduced on zram-over-swap, where
> > > many instance of memory hogs are running and laptop_mode is enabled.
> > > He said there was no problem when he disabled laptop_mode.
> > >
> > > The problem when I investigate problem is following as.
> > >
> > > Assumption for easy explanation: There are no page cache page in system
> > > because they all are already reclaimed.
> > >
> > > 1. try_to_free_pages disable may_writepage when laptop_mode is enabled.
> > > 2. shrink_inactive_list isolates victim pages from inactive anon lru list.
> > > 3. shrink_page_list adds them to swapcache via add_to_swap but it doesn't
> > > pageout because sc->may_writepage is 0 so the page is rotated back into
> > > inactive anon lru list. The add_to_swap made the page Dirty by SetPageDirty
> > > 4. 3 couldn't reclaim any pages so do_try_to_free_pages increase priority and
> > > retry reclaim with higher priority.
> > > 5. shrink_inactlive_list try to isolate victim pages from inactive anon lru list
> > > but got failed because it try to isolate pages with ISOLATE_CLEAN mode but
> > > inactive anon lru list is full of dirty pages by 3 so it just returns
> > > without any reclaim progress.
> > > 6. do_try_to_free_pages doesn't set may_write due to zero total_scanned.
> >
> > s/may_write/may_writepage/
>
> Thanks!
>
> >
> > > Because sc->nr_scanned is increased by shrink_page_list but we don't call
> > > shrink_page_list in 5 due to short of isolated pages.
> >
> > This is the bug, is it not?
> >
> > In laptop mode, we still need to write out dirty swapcache at some
> > point. An appropriate time to do this is when the scanning priority is
>
> Yes and when to some point is really important. Now, the point for that is
> depends on on the number of scanned pages by shrink_page_list. It means we
> must isolate victim pages from inactive LRU list and call shrink_page_list
> to increase sc->nr_scanned but unfortunately, we have various filters to
> decrease CPU consumption and LRU churning when VM try to isolate victim pages
> so it could prevent isolating victim pages from LRU list.
>
> > getting high. But it seems that this ISOLATE_CLEAN->total_scanned
>
> Yes. I absolutely agree on that some point should depend on priority, NOT
> the number of scanned pages. And I already said to you about that.
> https://lkml.org/lkml/2013/1/10/643
>
> We used to use such heuristic in several places in VM, ie DEF_PRIORITY - 2
> But why I hesitate with the patch is that I think this patch should go to
> stable tree so the patch should be really small and have no side effect so
> I don't wanted to change laptop_mode behavior heavily caused by changing
> condition for may_writepage trigger point.
>
> > interaction is preventing that.
> >
> > (An enhancement to laptop mode would be to opportunistically write out
> > dirty swapcache in or around laptop_mode_timer_fn()).
>
> It could but it should be another patch and VM shouldn't rely on ONLY
> laptop_mode_timer_fn, IMHO. VM should have own rule to reclaim pages
> regardless of laptop_mode's help to prevent OOM kill.
>
> >
> > > Above loop is continued until OOM happens.
> > > The problem didn't happen before [1] was merged because old logic's isolatation
> > > in shrink_inactive_list was successful and tried to call shrink_page_list
> > > to pageout them but it still ends up failed to page out by may_writepage.
> > > But important point is that sc->nr_scanned was increased althoug we couldn't
> > > swap out them so do_try_to_free_pages could set may_writepages.
> > > So this patch need to go stable tree althoug it's a band-aid.
> > > Then, for latest linus tree, we should fix laptop_mode's fundamental
> > > problem.
> >
> > Well. Perhaps we can do that now.
>
> Okay. If you don't object my suggestion, I will send patches next week.
> Thanks for the review, Andrew!
Andrew, If nobody objects, I would like to drop [1] and add ths patch instead of [1].
Luigi, below patch passed my test. If anybody doesn't object, could you test this
patch?
Thanks!
[1] mm: prevent addition of pages to swap if may_writepage is unset
-------------- &< --------------------
>From 94086dc7152359d052802c55c82ef19509fe8cce Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@...nel.org>
Date: Mon, 21 Jan 2013 10:43:43 +0900
Subject: [PATCH] mm: Use up free swap space before reaching OOM kill
Recently, Luigi reported there are lots of free swap space when
OOM happens. It's easily reproduced on zram-over-swap, where
many instance of memory hogs are running and laptop_mode is enabled.
He said there was no problem when he disabled laptop_mode.
The problem when I investigate problem is following as.
Assumption for easy explanation: There are no page cache page in system
because they all are already reclaimed.
1. try_to_free_pages disable may_writepage when laptop_mode is enabled.
2. shrink_inactive_list isolates victim pages from inactive anon lru list.
3. shrink_page_list adds them to swapcache via add_to_swap but it doesn't
pageout because sc->may_writepage is 0 so the page is rotated back into
inactive anon lru list. The add_to_swap made the page Dirty by SetPageDirty.
4. 3 couldn't reclaim any pages so do_try_to_free_pages increase priority and
retry reclaim with higher priority.
5. shrink_inactlive_list try to isolate victim pages from inactive anon lru list
but got failed because it try to isolate pages with ISOLATE_CLEAN mode but
inactive anon lru list is full of dirty pages by 3 so it just returns
without any reclaim progress.
6. do_try_to_free_pages doesn't set may_writepage due to zero total_scanned.
Because sc->nr_scanned is increased by shrink_page_list but we don't call
shrink_page_list in 5 due to short of isolated pages.
Above loop is continued until OOM happens.
The problem didn't happen before [1] was merged because old logic's
isolatation in shrink_inactive_list was successful and tried to call
shrink_page_list to pageout them but it still ends up failed to page out
by may_writepage. But important point is that sc->nr_scanned was increased
although we couldn't swap out them so do_try_to_free_pages could set
may_writepages.
Since [1] was introduced, it's not a good idea any more to depends on
only the number of scanned pages for setting may_writepage. So this patch
adds new trigger point of setting may_writepage as below DEF_PRIOIRTY - 2
which is used to show the significant memory pressure in VM so it's good
fit for our purpose which would be better to lose power saving or clickety
rather than OOM killing.
[1] f80c067[mm: zone_reclaim: make isolate_lru_page() filter-aware]
Reported-by: Luigi Semenzato <semenzato@...gle.com>
Signed-off-by: Minchan Kim <minchan@...nel.org>
---
mm/vmscan.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 740bad9..d333df0 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2204,6 +2204,13 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
goto out;
/*
+ * If we're getting trouble reclaiming, start doing
+ * writepage even in laptop mode.
+ */
+ if (sc->priority < DEF_PRIORITY - 2)
+ sc->may_writepage = 1;
+
+ /*
* Try to write back as many pages as we just scanned. This
* tends to cause slow streaming writers to write data to the
* disk smoothly, at the dirtying rate, which is nice. But
@@ -2774,12 +2781,10 @@ loop_again:
}
/*
- * If we've done a decent amount of scanning and
- * the reclaim ratio is low, start doing writepage
- * even in laptop mode
+ * If we're getting trouble reclaiming, start doing
+ * writepage even in laptop mode.
*/
- if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
- total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
+ if (sc.priority < DEF_PRIORITY - 2)
sc.may_writepage = 1;
if (zone->all_unreclaimable) {
--
1.7.9.5
>-
Kind regards,
Minchan Kim
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