Messages in this thread | | | Date | Mon, 6 Feb 2017 14:24:11 +0100 | From | Michal Hocko <> | Subject | Re: [PATCH 2/2 RESEND] mm: vmpressure: fix sending wrong events on underflow |
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On Mon 06-02-17 18:39:03, vinayak menon wrote: > On Mon, Feb 6, 2017 at 6:10 PM, Michal Hocko <mhocko@kernel.org> wrote: > > On Mon 06-02-17 17:54:10, Vinayak Menon wrote: > > [...] > >> diff --git a/mm/vmpressure.c b/mm/vmpressure.c > >> index 149fdf6..3281b34 100644 > >> --- a/mm/vmpressure.c > >> +++ b/mm/vmpressure.c > >> @@ -112,8 +112,10 @@ static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned, > >> unsigned long reclaimed) > >> { > >> unsigned long scale = scanned + reclaimed; > >> - unsigned long pressure; > >> + unsigned long pressure = 0; > >> > >> + if (reclaimed >= scanned) > >> + goto out; > > > > This deserves a comment IMHO. Besides that, why shouldn't we normalize > > the result already in vmpressure()? Please note that the tree == true > > path will aggregate both scanned and reclaimed and that already skews > > numbers. > Sure. Will add a comment. > IIUC, normalizing in vmpressure() means something like this which you > mentioned in one > of your previous emails right ? > > + if (reclaimed > scanned) > + reclaimed = scanned;
yes or scanned = reclaimed.
> Considering a scan window of 512 pages and without above piece of > code, if the first scanning is of a THP page > Scan=1,Reclaimed=512 > If the next 511 scans results in 0 reclaimed pages > total_scan=512,Reclaimed=512 => vmpressure 0
I am not sure I understand. What do you mean by next scans? We do not modify counters outside of vmpressure? If you mean next iteration of shrink_node's loop then this changeshouldn't make a difference, no?
> > Now with the above piece of code in place > Scan=1,Reclaimed=1, then > Scan=511, Reclaimed=0 > total_scan=512,Reclaimed=1 => critical vmpressure
-- Michal Hocko SUSE Labs
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