The patch titled
Subject: mm, page_alloc: reset the zone->watermark_boost early
has been added to the -mm tree. Its filename is
mm-page_alloc-reset-the-zone-watermark_boost-early.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-page_alloc-reset-the-zone-watermark_boost-early.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-page_alloc-reset-the-zone-watermark_boost-early.patch
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------------------------------------------------------
From: Charan Teja Reddy <charante@xxxxxxxxxxxxxx>
Subject: mm, page_alloc: reset the zone->watermark_boost early
Updating the zone watermarks by any means, like min_free_kbytes,
water_mark_scale_factor etc, when ->watermark_boost is set will result in
higher low and high watermarks than the user asked.
Below are the steps to reproduce the problem on system setup of Android
kernel running on Snapdragon hardware.
1) Default settings of the system are as below:
#cat /proc/sys/vm/min_free_kbytes = 5162
#cat /proc/zoneinfo | grep -e boost -e low -e "high " -e min -e Node
Node 0, zone Normal
min 797
low 8340
high 8539
2) Monitor the zone->watermark_boost(by adding a debug print in the
kernel) and whenever it is greater than zero value, write the same
value of min_free_kbytes obtained from step 1.
#echo 5162 > /proc/sys/vm/min_free_kbytes
3) Then read the zone watermarks in the system while the
->watermark_boost is zero. This should show the same values of
watermarks as step 1 but shown a higher values than asked.
#cat /proc/zoneinfo | grep -e boost -e low -e "high " -e min -e Node
Node 0, zone Normal
min 797
low 21148
high 21347
These higher values are because of updating the zone watermarks using the
macro min_wmark_pages(zone) which also adds the zone->watermark_boost.
#define min_wmark_pages(z) (z->_watermark[WMARK_MIN] +
z->watermark_boost)
So the steps that lead to the issue are:
1) On the extfrag event, watermarks are boosted by storing the required
value in ->watermark_boost.
2) User tries to update the zone watermarks level in the system through
min_free_kbytes or watermark_scale_factor.
3) Later, when kswapd woke up, it resets the zone->watermark_boost to
zero.
In step 2), we use the min_wmark_pages() macro to store the watermarks
in the zone structure thus the values are always offsetted by
->watermark_boost value. This can be avoided by resetting the
->watermark_boost to zero before it is used.
Link: http://lkml.kernel.org/r/1589457511-4255-1-git-send-email-charante@xxxxxxxxxxxxxx
Signed-off-by: Charan Teja Reddy <charante@xxxxxxxxxxxxxx>
Reviewed-by: Baoquan He <bhe@xxxxxxxxxx>
Cc: Vinayak Menon <vinmenon@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/page_alloc.c~mm-page_alloc-reset-the-zone-watermark_boost-early
+++ a/mm/page_alloc.c
@@ -7780,9 +7780,9 @@ static void __setup_per_zone_wmarks(void
mult_frac(zone_managed_pages(zone),
watermark_scale_factor, 10000));
+ zone->watermark_boost = 0;
zone->_watermark[WMARK_LOW] = min_wmark_pages(zone) + tmp;
zone->_watermark[WMARK_HIGH] = min_wmark_pages(zone) + tmp * 2;
- zone->watermark_boost = 0;
spin_unlock_irqrestore(&zone->lock, flags);
}
_
Patches currently in -mm which might be from charante@xxxxxxxxxxxxxx are
mm-page_alloc-reset-the-zone-watermark_boost-early.patch
