[PATCH v4] tmpfs: don't enable large folios if not supported

[Kefeng Wang <wangkefeng.wang@huawei.com>]

The tmpfs could support large folio, but there is some configurable
options(mount options and runtime deny/force) to enable/disable large
folio allocation, so there is a performance issue when perform write
without large folio, the issue is similar to commit 4e527d5841e2
("iomap: fault in smaller chunks for non-large folio mappings").

Since 'deny' for emergencies and 'force' for testing, performence issue
should not be a problem in the real production environments, so only
don't call mapping_set_large_folios() in __shmem_get_inode() when
large folio is disabled with mount huge=never option(default policy).

Fixes: 9aac777aaf94 ("filemap: Convert generic_perform_write() to support large folios")
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
---
v4:
- only fix mount huge=never since runtime deny/force just for
  emergencies/testing, suggested by Baolin
v3:
- don't enable large folio suppport in __shmem_get_inode() if disabled,
  suggested by Matthew.
v2:
- Don't use IOCB flags

 mm/shmem.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index e933327d8dac..74ef214dc1a7 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2827,7 +2827,10 @@ static struct inode *__shmem_get_inode(struct mnt_idmap *idmap,
 	cache_no_acl(inode);
 	if (sbinfo->noswap)
 		mapping_set_unevictable(inode->i_mapping);
-	mapping_set_large_folios(inode->i_mapping);
+
+	/* Don't consider 'deny' for emergencies and 'force' for testing */
+	if (sbinfo->huge)
+		mapping_set_large_folios(inode->i_mapping);
 
 	switch (mode & S_IFMT) {
 	default:
-- 
2.27.0