On 05/14/20 at 05:28pm, Charan Teja Reddy wrote: > Updating the zone watermarks by any means, like min_free_kbytes, > water_mark_scale_factor e.t.c, when ->watermark_boost is set will result > into the higher low and high watermarks than the user asked. > > Below are the steps pursued 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 is like below: > 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. > > Signed-off-by: Charan Teja Reddy <charante@xxxxxxxxxxxxxx> > --- > > v2: Improve the commit message > > v1: (https://patchwork.kernel.org/patch/11540751/) > > mm/page_alloc.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index cef05d3..d001d61 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -7761,9 +7761,9 @@ 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; Yeah, watermark_boost is a temporary value which is used for reclaim, and will be reset after reclaim finished. Here we should respect the watermark setting from user. This fix looks good to me. Reviewed-by: Baoquan He <bhe@xxxxxxxxxx> > > spin_unlock_irqrestore(&zone->lock, flags); > } > -- > QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a > member of the Code Aurora Forum, hosted by The Linux Foundation >
