[RFC PATCH 07/12] mm/compaction: optionally use a different isolate function

[Frank van der Linden <fvdl@google.com>]

For CMA balancing, the compaction migration hooks can largely
be reused, except a different function to isolate free pages
is needed.

So, add a pointer to the isolation function in the compact_control
structure. If it's not NULL, use it, else use isolate_freepages as
usual.

No functional change.

Signed-off-by: Frank van der Linden <fvdl@google.com>
---
 mm/compaction.c | 5 ++++-
 mm/internal.h   | 5 +++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index bf021b31c7ec..6a2c06e356c5 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1813,7 +1813,10 @@ static struct folio *compaction_alloc_noprof(struct folio *src, unsigned long da
 	if (start_order == NR_PAGE_ORDERS) {
 		if (has_isolated_pages)
 			return NULL;
-		isolate_freepages(cc);
+		if (cc->isolate_freepages)
+			cc->isolate_freepages(cc);
+		else
+			isolate_freepages(cc);
 		has_isolated_pages = true;
 		goto again;
 	}
diff --git a/mm/internal.h b/mm/internal.h
index 45b725c3dc03..7916d8be8922 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -873,6 +873,11 @@ struct compact_control {
 	unsigned int nr_freepages;	/* Number of isolated free pages */
 	unsigned int nr_migratepages;	/* Number of pages to migrate */
 	unsigned long free_pfn;		/* isolate_freepages search base */
+	/*
+	 * Function to use to isolate free pages, if applicable. If NULL,
+	 * default to isolate_freepages().
+	 */
+	void (*isolate_freepages)(struct compact_control *cc);
 	/*
 	 * Acts as an in/out parameter to page isolation for migration.
 	 * isolate_migratepages uses it as a search base.
-- 
2.51.0.384.g4c02a37b29-goog