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

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

This reverts commit 5a90c155defa684f3a21f68c3f8e40c056e6114c.

Currently, when shmem mounts are initialized, they only use 'sbinfo->huge' to
determine whether the shmem mount supports large folios. However, for anonymous
shmem, whether it supports large folios can be dynamically configured via sysfs
interfaces, so setting or not setting mapping_set_large_folios() during initialization
cannot accurately reflect whether anonymous shmem actually supports large folios,
which has already caused some confusion[1].

Moreover, for tmpfs mounts, relying on 'sbinfo->huge' cannot keep the mapping_set_large_folios()
setting consistent across all mappings in the entire tmpfs mount. In other words,
under the same tmpfs mount, after remount, we might end up with some mappings
supporting large folios (calling mapping_set_large_folios()) while others don't.

After some investigation, I found that the write performance regression addressed
by commit 5a90c155defa has already been fixed by the following commit 665575cff098b
("filemap: move prefaulting out of hot write path"). See the following test data:

Base:
dd if=/dev/zero of=/mnt/tmpfs/test bs=400K count=10485 (3.2 GB/s)
dd if=/dev/zero of=/mnt/tmpfs/test bs=800K count=5242 (3.2 GB/s)
dd if=/dev/zero of=/mnt/tmpfs/test bs=1600K count=2621 (3.1 GB/s)
dd if=/dev/zero of=/mnt/tmpfs/test bs=2200K count=1906 (3.0 GB/s )
dd if=/dev/zero of=/mnt/tmpfs/test bs=3000K count=1398 (3.0 GB/s)
dd if=/dev/zero of=/mnt/tmpfs/test bs=4500K count=932 (3.1 GB/s)

Base + revert 5a90c155defa:
dd if=/dev/zero of=/mnt/tmpfs/test bs=400K count=10485 (3.3 GB/s)
dd if=/dev/zero of=/mnt/tmpfs/test bs=800K count=5242 (3.3 GB/s)
dd if=/dev/zero of=/mnt/tmpfs/test bs=1600K count=2621 (3.2 GB/s)
dd if=/dev/zero of=/mnt/tmpfs/test bs=2200K count=1906 (3.1 GB/s)
dd if=/dev/zero of=/mnt/tmpfs/testbs=3000K count=1398 (3.0 GB/s)
dd if=/dev/zero of=/mnt/tmpfs/test bs=4500K count=932 (3.1 GB/s)

The data is basically consistent with minor fluctuation noise. So we can now
safely revert commit 5a90c155defa to set mapping_set_large_folios() for all
shmem mounts unconditionally.

[1] https://lore.kernel.org/all/ec927492-4577-4192-8fad-85eb1bb43121@linux.alibaba.com/
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
Note: for more investigation and test data, see:
https://lore.kernel.org/all/116df9f9-4db7-40d4-a4a4-30a87c0feffa@linux.alibaba.com/
Thanks Kefeng for confirming the performance issue.
---
 mm/shmem.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 4ecefe02881d..dafbea53b22d 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -3087,10 +3087,7 @@ static struct inode *__shmem_get_inode(struct mnt_idmap *idmap,
 	cache_no_acl(inode);
 	if (sbinfo->noswap)
 		mapping_set_unevictable(inode->i_mapping);
-
-	/* Don't consider 'deny' for emergencies and 'force' for testing */
-	if (sbinfo->huge)
-		mapping_set_large_folios(inode->i_mapping);
+	mapping_set_large_folios(inode->i_mapping);
 
 	switch (mode & S_IFMT) {
 	default:
-- 
2.47.3