Hi William,
William Lam <william.lam@xxxxxxxxxxxxx> writes:
> The number of scanned pages can be lower than the number of isolated
> pages when isolating mirgratable or free pageblock. The metric is being
> reported in trace event and also used in vmstat.
>
> This behaviour is confusing since currently the count for isolated pages
> takes account of compound page but not for the case of scanned pages.
> And given that the number of isolated pages(nr_taken) reported in
> mm_compaction_isolate_template trace event is on a single-page basis,
> the ambiguity when reporting the number of scanned pages can be removed
> by also including compound page count.
A minor suggestion - It maybe useful to include an example trace output
to highlight the issue.
>
> Signed-off-by: William Lam <william.lam@xxxxxxxxxxxxx>
> ---
> mm/compaction.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 1f89b969c12b..1b51cf2d32b6 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -616,6 +616,7 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
> break;
> set_page_private(page, order);
>
> + nr_scanned += isolated - 1;
> total_isolated += isolated;
> cc->nr_freepages += isolated;
> list_add_tail(&page->lru, freelist);
> @@ -1101,6 +1102,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> isolate_success_no_list:
> cc->nr_migratepages += compound_nr(page);
> nr_isolated += compound_nr(page);
> + nr_scanned += compound_nr(page) - 1;
>
> /*
> * Avoid isolating too much unless this block is being
> @@ -1504,6 +1506,7 @@ fast_isolate_freepages(struct compact_control *cc)
> if (__isolate_free_page(page, order)) {
> set_page_private(page, order);
> nr_isolated = 1 << order;
> + nr_scanned += nr_isolated - 1;
> cc->nr_freepages += nr_isolated;
> list_add_tail(&page->lru, &cc->freepages);
> count_compact_events(COMPACTISOLATED, nr_isolated);
Regardless of the comment above -
Reviewed-by: Punit Agrawal <punit.agrawal@xxxxxxxxxxxxx>
