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Some entries in memory_idle_ms_percentiles then keep their old values instead of being updated. For example, a 256 MiB i386 QEMU guest reported p0=19200 ms, but p50 and p100 were both zero. Cast accounted_bytes to u64 before multiplying and use div64_ul() for the division. Compute the percentage once per region. Link: https://lore.kernel.org/r/CANOyQmHad1vamnZT12M5yPrJ69==Pt1U0+MGw6u0MuNtr-DRCw@mail.gmail.com Signed-off-by: Aveline Noir --- This is against mm-new ad9f2d463666. With the fix, the original test reports p0=p50=p100=19200 ms. The i386 kernel build, x86_64 W=1 stat.o build and external arithmetic checks passed. I also ran 38 before/after VM tests and 20 same-image controls. Throughput was close overall, but median kdamond CPU rose by 0.0053 and 0.0221 percentage points of one guest CPU for stream and sparse, respectively. Some pairs had 5.91% lower throughput or 15.49% higher scan P99. So I can't yet tell whether these differences come from the patch. mm/damon/stat.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/mm/damon/stat.c b/mm/damon/stat.c index b05b68f73e10..eccd372810d0 100644 --- a/mm/damon/stat.c +++ b/mm/damon/stat.c @@ -114,7 +114,7 @@ static void damon_stat_set_idletime_percentiles(struct damon_ctx *c) { struct damon_region **sorted_regions, *region; int nr_regions; - unsigned long total_sz, accounted_bytes = 0; + unsigned long total_sz, accounted_bytes = 0, percentile; int err, i, next_percentile = 0; err = damon_stat_sort_regions(c, &sorted_regions, &nr_regions, @@ -124,7 +124,8 @@ static void damon_stat_set_idletime_percentiles(struct damon_ctx *c) for (i = 0; i < nr_regions; i++) { region = sorted_regions[i]; accounted_bytes += region->ar.end - region->ar.start; - while (next_percentile <= accounted_bytes * 100 / total_sz) + percentile = div64_ul((u64)accounted_bytes * 100, total_sz); + while (next_percentile <= percentile) memory_idle_ms_percentiles[next_percentile++] = damon_stat_idletime(region) * (long)c->attrs.aggr_interval / USEC_PER_MSEC;