Mention the trade-off between waiting for writeback and potentially
causing hot cache refaults in the code where we make this decisions
and activate writeback pages.
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---
mm/vmscan.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 70103f411247..ae3d982216b5 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1056,6 +1056,15 @@ static unsigned long shrink_page_list(struct list_head *page_list,
* throttling so we could easily OOM just because too many
* pages are in writeback and there is nothing else to
* reclaim. Wait for the writeback to complete.
+ *
+ * In cases 1) and 2) we activate the pages to get them out of
+ * the way while we continue scanning for clean pages on the
+ * inactive list and refilling from the active list. The
+ * observation here is that waiting for disk writes is more
+ * expensive than potentially causing reloads down the line.
+ * Since they're marked for immediate reclaim, they won't put
+ * memory pressure on the cache working set any longer than it
+ * takes to write them to disk.
*/
if (PageWriteback(page)) {
/* Case 1 above */
--
2.11.0
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