@@ -1882,6 +1882,7 @@ static struct folio *compaction_alloc(struct folio *src, unsigned long data)
if (order)
prep_compound_page(&dst->page, order);
cc->nr_freepages -= 1 << order;
+ cc->nr_migratepages -= 1 << order;
return page_rmappable_folio(&dst->page);
}
@@ -1904,6 +1905,7 @@ static void compaction_free(struct folio *dst, unsigned long data)
list_add(&dst->lru, &cc->freepages[order].pages);
cc->freepages[order].nr_pages++;
cc->nr_freepages += 1 << order;
+ cc->nr_migratepages += 1 << order;
}
/* possible outcome of isolate_migratepages */
Currently we will use 'cc->nr_freepages >= cc->nr_migratepages' comparison to ensure that enough freepages are isolated in isolate_freepages(), however it just decreases the cc->nr_freepages without updating cc->nr_migratepages in compaction_alloc(), which will waste more CPU cycles and cause too many freepages to be isolated. So we should also update the cc->nr_migratepages when allocating or freeing the freepages to avoid isolating excess freepages. And I can see fewer free pages are scanned and isolated when running thpcompact on my Arm64 server: k6.7 k6.7_patched Ops Compaction pages isolated 120692036.00 118160797.00 Ops Compaction migrate scanned 131210329.00 154093268.00 Ops Compaction free scanned 1090587971.00 1080632536.00 Ops Compact scan efficiency 12.03 14.26 Moreover, I did not see an obvious latency improvements, this is likely because isolating freepages is not the bottleneck in the thpcompact test case. k6.7 k6.7_patched Amean fault-both-1 1089.76 ( 0.00%) 1080.16 * 0.88%* Amean fault-both-3 1616.48 ( 0.00%) 1636.65 * -1.25%* Amean fault-both-5 2266.66 ( 0.00%) 2219.20 * 2.09%* Amean fault-both-7 2909.84 ( 0.00%) 2801.90 * 3.71%* Amean fault-both-12 4861.26 ( 0.00%) 4733.25 * 2.63%* Amean fault-both-18 7351.11 ( 0.00%) 6950.51 * 5.45%* Amean fault-both-24 9059.30 ( 0.00%) 9159.99 * -1.11%* Amean fault-both-30 10685.68 ( 0.00%) 11399.02 * -6.68%* Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com> --- Changes from v1: - Rebased on the latest mm-unstable branch. --- mm/compaction.c | 2 ++ 1 file changed, 2 insertions(+)