[v3 PATCH 3/5] mm: migrate: skip shared exec THP for NUMA balancing

[Yang Shi]

The NUMA balancing skip shared exec base page.  Since
CONFIG_READ_ONLY_THP_FOR_FS was introduced, there are probably shared
exec THP, so skip such THPs for NUMA balancing as well.

And Willy's regular filesystem THP support patches could create shared
exec THP wven without that config.

In addition, the page_is_file_lru() is used to tell if the page is file
cache or not, but it filters out shmem page.  It sounds like a typical
usecase by putting executables in shmem to achieve performance gain via
using shmem-THP, so it sounds worth skipping migration for such case too.

Signed-off-by: Yang Shi <shy828301@xxxxxxxxx>
---
 mm/migrate.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index d7167f7107bd..18cc1ef0e447 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2069,6 +2069,17 @@ bool pmd_trans_migrating(pmd_t pmd)
 	return PageLocked(page);
 }
 
+static inline bool is_shared_exec_page(struct vm_area_struct *vma,
+				       struct page *page)
+{
+	if (page_mapcount(page) != 1 &&
+	    (page_is_file_lru(page) || vma_is_shmem(vma)) &&
+	    (vma->vm_flags & VM_EXEC))
+		return true;
+
+	return false;
+}
+
 /*
  * Attempt to migrate a misplaced page to the specified destination
  * node. Caller is expected to have an elevated reference count on
@@ -2086,8 +2097,7 @@ int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
 	 * Don't migrate file pages that are mapped in multiple processes
 	 * with execute permissions as they are probably shared libraries.
 	 */
-	if (page_mapcount(page) != 1 && page_is_file_lru(page) &&
-	    (vma->vm_flags & VM_EXEC))
+	if (is_shared_exec_page(vma, page))
 		goto out;
 
 	/*
@@ -2142,6 +2152,9 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
 	int page_lru = page_is_file_lru(page);
 	unsigned long start = address & HPAGE_PMD_MASK;
 
+	if (is_shared_exec_page(vma, page))
+		goto out;
+
 	new_page = alloc_pages_node(node,
 		(GFP_TRANSHUGE_LIGHT | __GFP_THISNODE),
 		HPAGE_PMD_ORDER);
@@ -2253,6 +2266,7 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
 
 out_unlock:
 	unlock_page(page);
+out:
 	put_page(page);
 	return 0;
 }
-- 
2.26.2