| Message ID | 20250110122133.423481-1-lizhijian@fujitsu.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [1/2] mm/vmscan: Accumulate nr_demoted for accurate demotion statistics | expand |
On Fri, Jan 10, 2025 at 08:21:32PM +0800, Li Zhijian wrote: > In the shrink_folio_list() function, demote_folio_list() can be called > multiple times, which can lead to inaccurate demotion statistics if the > number of demoted pages is not accumulated correctly. It looks like demotion will only be attempted once. On the second pass, do_demote_pass will be false, demote_folios will be empty and demote_folio_list() will do nothing. But I guess there is no harm in making nr_demoted an accumulation for less confusion in the future...
＞ It looks like demotion will only be attempted once. On the second pass, do_demote_pass will be false, demote_folios will be empty and demote_folio_list() will do nothing. But I guess there is no harm in making nr_demoted an accumulation for less confusion in the future... Emm, after checked the code again, it seems you are right. But this can not explain why i got inaccurate demotion statistics from /proc/vmstat compared to the value i counted in the code myself days ago. thanks for your feedback, i will take a look next week. Get Outlook for Android<https://aka.ms/AAb9ysg>
> Emm, after checked the code again, it seems you are right. But this can not explain why i got inaccurate demotion statistics from /proc/vmstat compared to the value i counted in the code myself days ago.
Well... I know what was going on, the second pass will override stat-＞nr_demoted to be *zero* that makes the first try stat-＞nr_demoted got lost.
Get Outlook for Android<https://aka.ms/AAb9ysg>
> Well... I know what was going on, the second pass will override stat-＞nr_demoted to be *zero* that makes the first try stat-＞nr_demoted got lost. Ah you are right. This is a bug when demotion partially succeeds in the first pass. Thanks for catching it. Acked-by: Kaiyang Zhao <kaiyang2@cs.cmu.edu>
diff --git a/mm/vmscan.c b/mm/vmscan.c index 9a859b7d18d7..430d580e37dd 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1522,7 +1522,7 @@ static unsigned int shrink_folio_list(struct list_head *folio_list, /* 'folio_list' is always empty here */ /* Migrate folios selected for demotion */ - stat->nr_demoted = demote_folio_list(&demote_folios, pgdat); + stat->nr_demoted += demote_folio_list(&demote_folios, pgdat); nr_reclaimed += stat->nr_demoted; /* Folios that could not be demoted are still in @demote_folios */ if (!list_empty(&demote_folios)) {
In the shrink_folio_list() function, demote_folio_list() can be called multiple times, which can lead to inaccurate demotion statistics if the number of demoted pages is not accumulated correctly. Accumulate the nr_demoted count across multiple calls to demote_folio_list(), ensuring accurate reporting of demotion statistics. Fixes: f77f0c751478 ("mm,memcg: provide per-cgroup counters for NUMA balancing operations") Signed-off-by: Li Zhijian <lizhijian@fujitsu.com> --- mm/vmscan.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)