On Fri, Feb 16, 2024 at 2:24 AM Byungchul Park <byungchul@xxxxxx> wrote: > > On Fri, Feb 16, 2024 at 12:55:17AM -0500, Yu Zhao wrote: > > On Thu, Feb 8, 2024 at 1:18 AM Byungchul Park <byungchul@xxxxxx> wrote: > > > > > > With cache_trim_mode on, reclaim logic doesn't bother reclaiming anon > > > pages. However, it should be more careful to turn on the mode because > > > it's going to prevent anon pages from reclaimed even if there are huge > > > ammount of anon pages that are very cold so should be reclaimed. Even > > > worse, that can lead kswapd_failures to be MAX_RECLAIM_RETRIES and stop > > > until direct reclaim eventually works to resume kswapd. > > > > Is a theory or something observed in the real world? If it's the > > former, would this change risk breaking existing use cases? It's the > > I faced the latter case. > > > latter, where are the performance numbers to show what it looks like > > before and after this patch? Let me ask again: where are the performance numbers to show what it looks like before and after this patch? > Before: > > Whenever the system meets the condition to turn on cache_trim_mode but > few cache pages to trim, kswapd fails without scanning anon pages that > are plenty and cold for sure and it retries 8 times and looks *stopped > for ever*. > > After: > > When the system meets the condition to turn on cache_trim_mode but few > cache pages to trim, kswapd finally works at the highest scan priority. > So kswap looks working well even in the same condition. These are not performance numbers -- what test cases can prove what's described here? > > > Signed-off-by: Byungchul Park <byungchul@xxxxxx> > > > --- > > > mm/vmscan.c | 3 ++- > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > > index bba207f41b14..25b55fdc0d41 100644 > > > --- a/mm/vmscan.c > > > +++ b/mm/vmscan.c > > > @@ -2268,7 +2268,8 @@ static void prepare_scan_control(pg_data_t *pgdat, struct scan_control *sc) > > > * anonymous pages. > > > */ > > > file = lruvec_page_state(target_lruvec, NR_INACTIVE_FILE); > > > - if (file >> sc->priority && !(sc->may_deactivate & DEACTIVATE_FILE)) > > > + if (sc->priority != 1 && file >> sc->priority & > > > > Why 1? > > It means the highest scan priority. The priority goes from DEF_PRIORITY > to 1. This is not true -- sc->priority can go all the way to zero. > Byungchul > > > > + !(sc->may_deactivate & DEACTIVATE_FILE)) > > > sc->cache_trim_mode = 1; > > > else > > > sc->cache_trim_mode = 0;
