[RFC PATCH] mm: khugepaged: decouple SHMEM and file folios' collapse

[Baolin Wang <baolin.wang@linux.alibaba.com>]

Originally, the file pages collapse was intended for tmpfs/shmem to merge
into THP in the background. However, now not only tmpfs/shmem can support
large folios, but some other file systems (such as XFS, erofs ...) also
support large folios. Therefore, it is time to decouple the support of
file folios collapse from SHMEM.

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
 mm/Kconfig      |  2 +-
 mm/khugepaged.c | 13 ++-----------
 2 files changed, 3 insertions(+), 12 deletions(-)

diff --git a/mm/Kconfig b/mm/Kconfig
index 713b29232e94..42be19d82c7f 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -898,7 +898,7 @@ config THP_SWAP
 
 config READ_ONLY_THP_FOR_FS
 	bool "Read-only THP for filesystems (EXPERIMENTAL)"
-	depends on TRANSPARENT_HUGEPAGE && SHMEM
+	depends on TRANSPARENT_HUGEPAGE
 
 	help
 	  Allow khugepaged to put read-only file-backed pages in THP.
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index ebcd7c8a4b44..cdf5a581368b 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1464,7 +1464,6 @@ static void collect_mm_slot(struct khugepaged_mm_slot *mm_slot)
 	}
 }
 
-#ifdef CONFIG_SHMEM
 /* folio must be locked, and mmap_lock must be held */
 static int set_huge_pmd(struct vm_area_struct *vma, unsigned long addr,
 			pmd_t *pmdp, struct folio *folio, struct page *page)
@@ -2353,14 +2352,6 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
 	trace_mm_khugepaged_scan_file(mm, folio, file, present, swap, result);
 	return result;
 }
-#else
-static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
-				    struct file *file, pgoff_t start,
-				    struct collapse_control *cc)
-{
-	BUILD_BUG();
-}
-#endif
 
 static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
 					    struct collapse_control *cc)
@@ -2436,7 +2427,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
 			VM_BUG_ON(khugepaged_scan.address < hstart ||
 				  khugepaged_scan.address + HPAGE_PMD_SIZE >
 				  hend);
-			if (IS_ENABLED(CONFIG_SHMEM) && !vma_is_anonymous(vma)) {
+			if (!vma_is_anonymous(vma)) {
 				struct file *file = get_file(vma->vm_file);
 				pgoff_t pgoff = linear_page_index(vma,
 						khugepaged_scan.address);
@@ -2782,7 +2773,7 @@ int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev,
 		mmap_assert_locked(mm);
 		memset(cc->node_load, 0, sizeof(cc->node_load));
 		nodes_clear(cc->alloc_nmask);
-		if (IS_ENABLED(CONFIG_SHMEM) && !vma_is_anonymous(vma)) {
+		if (!vma_is_anonymous(vma)) {
 			struct file *file = get_file(vma->vm_file);
 			pgoff_t pgoff = linear_page_index(vma, addr);
 
-- 
2.43.5