On Wed, Nov 29, 2023 at 09:01:26PM +0800, Zhiguo Jiang wrote: > It is needed to ensure sc->nr.unqueued_dirty > 0, which can avoid to > set PGDAT_DIRTY flag when sc->nr.unqueued_dirty and sc->nr.file_taken > are both zero at the same time. Have you observed this happening, or is this from code review? > It can't be guaranteed for the PGDAT_WRITEBACK flag that only pages > marked for immediate reclaim are on evictable LRUs in other following > shrink processes of the same kswapd shrink recycling. So when both a > small amount of pages marked for immediate reclaim and a large amount > of pages marked for non-immediate reclaim are on evictable LRUs at the > same time, if it's only determined that there is at least a page marked > for immediate reclaim on evictable LRUs, kswapd shrink is throttled to > sleep, which will increase kswapd process consumption. > > It can be fixed to throttle kswapd shrink when sc->nr.immediate is equal > to sc->nr.file_taken. So you're fixing two distinct things in the same patch? > +++ b/mm/vmscan.c > @@ -5915,17 +5915,17 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc) > set_bit(PGDAT_WRITEBACK, &pgdat->flags); > > /* Allow kswapd to start writing pages during reclaim.*/ > - if (sc->nr.unqueued_dirty == sc->nr.file_taken) > + if (sc->nr.unqueued_dirty && sc->nr.unqueued_dirty == sc->nr.file_taken) > set_bit(PGDAT_DIRTY, &pgdat->flags); > > /* > - * If kswapd scans pages marked for immediate > + * If kswapd scans massive pages marked for immediate I don't understand why you've added the word "massive". Do you mean that the pages are large, or that kswapd has scanned a lot of pages? > * reclaim and under writeback (nr_immediate), it > * implies that pages are cycling through the LRU > * faster than they are written so forcibly stall > * until some pages complete writeback. > */ > - if (sc->nr.immediate) > + if (sc->nr.immediate && sc->nr.immediate == sc->nr.file_taken) > reclaim_throttle(pgdat, VMSCAN_THROTTLE_WRITEBACK); > }
