| Message ID | 20231129130126.2130-1-justinjiang@vivo.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm:vmscan: fix shrink sc->nr counter values issue | expand |
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); > }
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); >> }
On Thu, Nov 30, 2023 at 09:56:59AM +0800, zhiguojiang wrote: > > > - * 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. Then the word "many" communicates your meaning better. "massive" would mean that each page is very big, while "many" means that there are a lot of pages. It was foolish to send out a v2 so swiftly. Best wait for someone who's familiar with this code to respond to it now that you've clarified what you were doing.
在 2023/11/30 11:29, Matthew Wilcox 写道: > On Thu, Nov 30, 2023 at 09:56:59AM +0800, zhiguojiang wrote: >>>> - * 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. > Then the word "many" communicates your meaning better. "massive" would > mean that each page is very big, while "many" means that there are a > lot of pages. > > It was foolish to send out a v2 so swiftly. Best wait for someone who's > familiar with this code to respond to it now that you've clarified what > you were doing. Thanks for you suggestions, I will update the newer version patch later.
diff --git a/mm/vmscan.c b/mm/vmscan.c index d8c3338fee0f..5723672bbdc2 --- a/mm/vmscan.c +++ 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 * 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); }
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. 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. Signed-off-by: Zhiguo Jiang <justinjiang@vivo.com> --- mm/vmscan.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) mode change 100644 => 100755 mm/vmscan.c