在 2023/11/29 23:17, Matthew Wilcox 写道:
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?
Found in code review. The other sc->nr parameters are also judged whether they themselves are zero first in shrink_node.
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?
It can be understood as two issues, and I will submit them separately.
+++ 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?
The added "massive" means that there are a large number of pages marked
for immediate reclaim on evictable LRUs.
The added "massive" is relative to the situation that there is only a
small amount of pages marked for immediate reclaim or even only one page
marked for immediate reclaim on the evictable LRUs for throttle kswapd,
and I think this situation don't need to throttle, because there may be
other types of pages on evictable LRUs.
* 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);
}
