[PATCH RESEND] avoid swapping out with swappiness==0

[PATCH RESEND] avoid swapping out with swappiness==0

[Satoru Moriya]

Hi Andrew,

This patch has been reviewed for couple of months.

This patch *only* improves the behavior when the kernel has
enough filebacked pages. It means that it does not change
the behavior when kernel has small number of filebacked pages.

Kosaki-san pointed out that the threshold which we use
to decide whether filebacked page is enough or not is not
appropriate(*).

(*) http://www.spinics.net/lists/linux-mm/msg32380.html

As I described in (**), I believe that threshold discussion
should be done in other thread because it affects not only
swappiness=0 case and the kernel behave the same way with
or without this patch below the threshold.

(**) http://www.spinics.net/lists/linux-mm/msg34317.html

The patch may not be perfect but, at least, we can improve
the kernel behavior in the enough filebacked memory case
with this patch. I believe it's better than nothing.

Do you have any comments about it?

NOTE: I updated the patch with Acked-by tags

---
Sometimes we'd like to avoid swapping out anonymous memory
in particular, avoid swapping out pages of important process or
process groups while there is a reasonable amount of pagecache
on RAM so that we can satisfy our customers' requirements.

OTOH, we can control how aggressive the kernel will swap memory pages
with /proc/sys/vm/swappiness for global and
/sys/fs/cgroup/memory/memory.swappiness for each memcg.

But with current reclaim implementation, the kernel may swap out
even if we set swappiness==0 and there is pagecache on RAM.

This patch changes the behavior with swappiness==0. If we set
swappiness==0, the kernel does not swap out completely
(for global reclaim until the amount of free pages and filebacked
pages in a zone has been reduced to something very very small
(nr_free + nr_filebacked < high watermark)).

Any comments are welcome.

Regards,
Satoru Moriya

Signed-off-by: Satoru Moriya <satoru.moriya@hds.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Acked-by: Rik van Riel <riel@redhat.com>

---
 mm/vmscan.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 33dc256..52d64bf 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1983,10 +1983,10 @@ static void get_scan_count(struct mem_cgroup_zone *mz, struct scan_control *sc,
 	 * proportional to the fraction of recently scanned pages on
 	 * each list that were recently referenced and in active use.
 	 */
-	ap = (anon_prio + 1) * (reclaim_stat->recent_scanned[0] + 1);
+	ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
 	ap /= reclaim_stat->recent_rotated[0] + 1;
 
-	fp = (file_prio + 1) * (reclaim_stat->recent_scanned[1] + 1);
+	fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
 	fp /= reclaim_stat->recent_rotated[1] + 1;
 	spin_unlock_irq(&mz->zone->lru_lock);
 
@@ -1999,7 +1999,7 @@ out:
 		unsigned long scan;
 
 		scan = zone_nr_lru_pages(mz, lru);
-		if (priority || noswap) {
+		if (priority || noswap || !vmscan_swappiness(mz, sc)) {
 			scan >>= priority;
 			if (!scan && force_scan)
 				scan = SWAP_CLUSTER_MAX;
--
1.7.6.5

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Re: [PATCH RESEND] avoid swapping out with swappiness==0

[Rik van Riel]

On 05/23/2012 04:41 PM, Satoru Moriya wrote:

> The patch may not be perfect but, at least, we can improve
> the kernel behavior in the enough filebacked memory case
> with this patch. I believe it's better than nothing.

Agreed.

> Do you have any comments about it?

Only one comment, and it's for Andrew :)

> Signed-off-by: Satoru Moriya<satoru.moriya@hds.com>
> Acked-by: Minchan Kim<minchan@kernel.org>
> Acked-by: Rik van Riel<riel@redhat.com>

Andrew, you can turn my Acked-by into a

Reviewed-by: Rik van Riel<riel@redhat.com>

This is functionality that many people seem to want, and
will not break anything current users typically do.

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Re: [PATCH RESEND] avoid swapping out with swappiness==0

[Jerome Marchand]

On 05/23/2012 10:41 PM, Satoru Moriya wrote:
> Hi Andrew,
> 
> This patch has been reviewed for couple of months.
> 
> This patch *only* improves the behavior when the kernel has
> enough filebacked pages. It means that it does not change
> the behavior when kernel has small number of filebacked pages.
> 
> Kosaki-san pointed out that the threshold which we use
> to decide whether filebacked page is enough or not is not
> appropriate(*).
> 
> (*) http://www.spinics.net/lists/linux-mm/msg32380.html
> 
> As I described in (**), I believe that threshold discussion
> should be done in other thread because it affects not only
> swappiness=0 case and the kernel behave the same way with
> or without this patch below the threshold.
> 
> (**) http://www.spinics.net/lists/linux-mm/msg34317.html
> 
> The patch may not be perfect but, at least, we can improve
> the kernel behavior in the enough filebacked memory case
> with this patch. I believe it's better than nothing.
> 
> Do you have any comments about it?
> 
> NOTE: I updated the patch with Acked-by tags
> 
> ---
> Sometimes we'd like to avoid swapping out anonymous memory
> in particular, avoid swapping out pages of important process or
> process groups while there is a reasonable amount of pagecache
> on RAM so that we can satisfy our customers' requirements.
> 
> OTOH, we can control how aggressive the kernel will swap memory pages
> with /proc/sys/vm/swappiness for global and
> /sys/fs/cgroup/memory/memory.swappiness for each memcg.
> 
> But with current reclaim implementation, the kernel may swap out
> even if we set swappiness==0 and there is pagecache on RAM.
> 
> This patch changes the behavior with swappiness==0. If we set
> swappiness==0, the kernel does not swap out completely
> (for global reclaim until the amount of free pages and filebacked
> pages in a zone has been reduced to something very very small
> (nr_free + nr_filebacked < high watermark)).
> 
> Any comments are welcome.
> 
> Regards,
> Satoru Moriya
> 
> Signed-off-by: Satoru Moriya <satoru.moriya@hds.com>
> Acked-by: Minchan Kim <minchan@kernel.org>
> Acked-by: Rik van Riel <riel@redhat.com>
> 

Acked-by: Jerome Marchand <jmarchan@redhat.com>


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