Messages in this thread | | | Date | Tue, 11 Feb 2020 10:42:23 +0000 | From | Mel Gorman <> | Subject | Re: [RFC Patch] mm/vmscan.c: not inherit classzone_idx from previous reclaim |
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On Sun, Feb 09, 2020 at 03:41:45PM +0800, Wei Yang wrote: > Before commit e716f2eb24de ("mm, vmscan: prevent kswapd sleeping > prematurely due to mismatched classzone_idx"), classzone_idx could have > two possibilities on a new loop based on whether there is a wakeup > during reclaiming: > > * 0 if no wakeup > * the classzone_idx request by wakeup > > As described in the changelog, this commit is willing to change the > first case to (MAX_NR_ZONES - 1) to avoid some premature sleep. But it > does not achieve the goal. > > There are two versions of kswapd_classzone_idx() since this change: > > * commit e716f2eb24de ("mm, vmscan: prevent kswapd sleeping > prematurely due to mismatched classzone_idx") > * commit dffcac2cb88e ("mm/vmscan.c: prevent useless kswapd loops") > > Both of them would return the classzone_idx we passed as the 2nd > parameter when (pgdat->kswapd_classzone_idx == MAX_NR_ZONES). This > means if there is no wakeup during reclaiming, we would use > classzone_idx in previous round to sleep. >
This is somewhat intended.
> This patch fixes the logic by using (MAX_NR_ZONES - 1) for the first > case. >
Ok, what is the user-visible impact that is fixed by this patch or is this based on code review only? Please describe the test case exactly and the before and after results. I ask because this area is a magnet for regressions and intuitive ideas often lead to counter-intuitive results.
-- Mel Gorman SUSE Labs
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