| Message ID | 1589204408-5152-1-git-send-email-charante@codeaurora.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm, page_alloc: reset the zone->watermark_boost early | expand |
On Mon, 11 May 2020 19:10:08 +0530 Charan Teja Reddy <charante@codeaurora.org> wrote: > Updating the zone watermarks by any means, like extra_free_kbytes, > 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 > asks. This can be avoided by resetting the zone->watermark_boost to zero > early. Does this solve some problem which has been observed in testing? > ... > > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -7746,9 +7746,9 @@ 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); > } This could only be a problem if code is accessing these things without holding zone->lock. Is that ever the case?
Thank you Andrew for the reply. On 5/12/2020 1:41 AM, Andrew Morton wrote: > On Mon, 11 May 2020 19:10:08 +0530 Charan Teja Reddy <charante@codeaurora.org> wrote: > >> Updating the zone watermarks by any means, like extra_free_kbytes, >> 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 >> asks. This can be avoided by resetting the zone->watermark_boost to zero >> early. > > Does this solve some problem which has been observed in testing? Sorry, what are those issues observed in testing? It would be helpful If you post them here. > >> ... >> >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -7746,9 +7746,9 @@ 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); >> } > > This could only be a problem if code is accessing these things without > holding zone->lock. Is that ever the case? > This is a problem even when accessing these things with zone->lock held because we are directly using the macro min_wmark_pages(zone) which leads to the issue. Pasting macro here for reference. #define min_wmark_pages(z) (z->_watermark[WMARK_MIN] + z->watermark_boost) Steps that lead to the issue is like below: 1) On the extfrag event, we try to boost the watermark by storing the value in ->watermark_boost. 2) User changes the value of extra|min_free_kbytes or watermark_scale_factor. In __setup_perzone_wmarks, we directly store the user asked watermarks in the zones structure. In this step, the value is always offsets by ->watermark_boost as we use the min_wmark_pages() macro. 3) Later, when kswapd woke up, it resets the zone's watermark_boost to zero. Step 2 from the above is what resulting into the issue.
On 5/12/2020 7:01 PM, Charan Teja Kalla wrote: > > Thank you Andrew for the reply. > > On 5/12/2020 1:41 AM, Andrew Morton wrote: >> On Mon, 11 May 2020 19:10:08 +0530 Charan Teja Reddy <charante@codeaurora.org> wrote: >> >>> Updating the zone watermarks by any means, like extra_free_kbytes, >>> 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 >>> asks. This can be avoided by resetting the zone->watermark_boost to zero >>> early. >> >> Does this solve some problem which has been observed in testing? Sorry that I misunderstood your question. Yes it has solved problem of higher water marks seen in the zone than what I set through min_free_kbytes. Below are the steps I pursued to reproduce the problem 1) My system setup of Android kernel running on snapdragon hardware have the below settings as default: #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 boost 0 // This is the extra print I have added to check the boosting 2) Now I just try to change the zone watermark when the ->watermark_boost is greater than zero. I just write the same value of min_free_kbytes in which case we should have seen the watermarks same as default(I mean of step 1) #echo 5162 > /proc/sys/vm/min_free_kbytes But I have seen very high values of watermarks in the system, # cat /proc/zoneinfo | grep -e boost -e low -e "high " -e min -e Node Node 0, zone Normal min 797 low 21148 high 21347 boost 0 So, yes, this problem is got fixed with the changes made in this patch. > > Sorry, what are those issues observed in testing? It would be helpful > If you post them here. > >> >>> ... >>> >>> --- a/mm/page_alloc.c >>> +++ b/mm/page_alloc.c >>> @@ -7746,9 +7746,9 @@ 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); >>> } >> >> This could only be a problem if code is accessing these things without >> holding zone->lock. Is that ever the case? >> > > This is a problem even when accessing these things with zone->lock > held because we are directly using the macro min_wmark_pages(zone) > which leads to the issue. Pasting macro here for reference. > > #define min_wmark_pages(z) (z->_watermark[WMARK_MIN] + z->watermark_boost) > > Steps that lead to the issue is like below: > 1) On the extfrag event, we try to boost the watermark by storing the > value in ->watermark_boost. > > 2) User changes the value of extra|min_free_kbytes or watermark_scale_factor. > > In __setup_perzone_wmarks, we directly store the user asked > watermarks in the zones structure. In this step, the value > is always offsets by ->watermark_boost as we use the min_wmark_pages() macro. > > 3) Later, when kswapd woke up, it resets the zone's watermark_boost to zero. > > Step 2 from the above is what resulting into the issue. >
On Wed, 13 May 2020 15:16:53 +0530 Charan Teja Kalla <charante@codeaurora.org> wrote:
> So, yes, this problem is got fixed with the changes made in this patch.
OK, thanks.
Could you please prepare a v2 with a changelog which includes the
additional info in your two replies?
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 1b265b09..822e262 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -7746,9 +7746,9 @@ 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); }
Updating the zone watermarks by any means, like extra_free_kbytes, 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 asks. This can be avoided by resetting the zone->watermark_boost to zero early. Signed-off-by: Charan Teja Reddy <charante@codeaurora.org> --- mm/page_alloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)