| From: William Lam <william.lam@bytedance.com> |
| Subject: mm: compaction: include compound page count for scanning in pageblock isolation |
| Date: Mon, 11 Jul 2022 21:28:06 +0100 |
| |
| 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. |
| |
| some example output from trace where it shows nr_taken can be greater |
| than nr_scanned: |
| |
| Produced by kernel v5.19-rc6 |
| kcompactd0-42 [001] ..... 1210.268022: mm_compaction_isolate_migratepages: range=(0x107ae4 ~ 0x107c00) nr_scanned=265 nr_taken=255 |
| [...] |
| kcompactd0-42 [001] ..... 1210.268382: mm_compaction_isolate_freepages: range=(0x215800 ~ 0x215a00) nr_scanned=13 nr_taken=128 |
| kcompactd0-42 [001] ..... 1210.268383: mm_compaction_isolate_freepages: range=(0x215600 ~ 0x215680) nr_scanned=1 nr_taken=128 |
| |
| mm_compaction_isolate_migratepages does not seem to have this |
| behaviour, but for the reason of consistency, nr_scanned should also be |
| taken care of in that side. |
| |
| 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. |
| |
| Link: https://lkml.kernel.org/r/20220711202806.22296-1-william.lam@bytedance.com |
| Signed-off-by: William Lam <william.lam@bytedance.com> |
| Reviewed-by: Punit Agrawal <punit.agrawal@bytedance.com> |
| Cc: Mel Gorman <mgorman@techsingularity.net> |
| Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
| --- |
| |
| mm/compaction.c | 3 +++ |
| 1 file changed, 3 insertions(+) |
| |
| --- a/mm/compaction.c~mm-compaction-include-compound-page-count-for-scanning-in-pageblock-isolation |
| +++ a/mm/compaction.c |
| @@ -616,6 +616,7 @@ static unsigned long isolate_freepages_b |
| 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_success: |
| 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_co |
| 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); |
| _ |
