On 9/19/2023 1:20 AM, Zi Yan wrote:
On 18 Sep 2023, at 3:34, Baolin Wang wrote:
On 9/13/2023 12:28 AM, Zi Yan wrote:
From: Zi Yan <ziy@xxxxxxxxxx>
During migration in a memory compaction, free pages are placed in an array
of page lists based on their order. But the desired free page order (i.e.,
the order of a source page) might not be always present, thus leading to
migration failures. Split a high order free pages when source migration
page has a lower order to increase migration successful rate.
Note: merging free pages when a migration fails and a lower order free
page is returned via compaction_free() is possible, but there is too much
work. Since the free pages are not buddy pages, it is hard to identify
these free pages using existing PFN-based page merging algorithm.
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
---
mm/compaction.c | 40 +++++++++++++++++++++++++++++++++++++++-
1 file changed, 39 insertions(+), 1 deletion(-)
diff --git a/mm/compaction.c b/mm/compaction.c
index 868e92e55d27..45747ab5f380 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1801,9 +1801,46 @@ static struct folio *compaction_alloc(struct folio *src, unsigned long data)
struct compact_control *cc = (struct compact_control *)data;
struct folio *dst;
int order = folio_order(src);
+ bool has_isolated_pages = false;
+again:
if (!cc->freepages[order].nr_free) {
- isolate_freepages(cc);
+ int i;
+
+ for (i = order + 1; i <= MAX_ORDER; i++) {
+ if (cc->freepages[i].nr_free) {
+ struct page *freepage =
+ list_first_entry(&cc->freepages[i].pages,
+ struct page, lru);
+
+ int start_order = i;
+ unsigned long size = 1 << start_order;
+
+ list_del(&freepage->lru);
+ cc->freepages[i].nr_free--;
+
+ while (start_order > order) {
+ start_order--;
+ size >>= 1;
+
+ list_add(&freepage[size].lru,
+ &cc->freepages[start_order].pages);
+ cc->freepages[start_order].nr_free++;
+ set_page_private(&freepage[size], start_order);
IIUC, these split pages should also call functions to initialize? e.g. prep_compound_page()?
Not at this place. It is done right below and above "done" label. When free pages
are on cc->freepages, we want to keep them without being post_alloc_hook() or
prep_compound_page() processed for a possible future split. A free page is
only initialized when it is returned by compaction_alloc().
Ah, I see. Thanks for explanation.
