[PATCH v5 07/14] mm: shmem: allow THP support determination at folio allocation time

[Luiz Capitulino]

In order to enable THP support in shmem today, besides the user
configuration required, the CPU must support PMD-sized pages. This
is the case because of the following has_transparent_hugepage()
usage:

- shmem_parse_one() and shmem_parse_huge(): Check if THP is built-in and
  if the CPU supports PMD-sized pages

- shmem_init(): Since the CONFIG_TRANSPARENT_HUGEPAGE guard is outside
  the code block calling has_transparent_hugepage(), the
  has_transparent_hugepage() call is exclusively checking if the CPU
  supports PMD-sized pages

While it's necessary to check if CONFIG_TRANSPARENT_HUGEPAGE is enabled
in all cases, shmem can determine THP size support at folio allocation
time. Therefore, drop the has_transparent_hugepage() usage listed above
while keeping the CONFIG_TRANSPARENT_HUGEPAGE checks.

Additionally, we need to check if PMD size order is supported in
shmem_getattr(). Use pgtable_has_pmd_leaves() for that.

Signed-off-by: Luiz Capitulino <luizcap@xxxxxxxxxx>
---
 mm/shmem.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 88bc0c292f1a..108dc969b92a 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -689,7 +689,7 @@ static int shmem_parse_huge(const char *str)
 	else
 		return -EINVAL;
 
-	if (!has_transparent_hugepage() &&
+	if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
 	    huge != SHMEM_HUGE_NEVER && huge != SHMEM_HUGE_DENY)
 		return -EINVAL;
 
@@ -1303,6 +1303,8 @@ static int shmem_getattr(struct mnt_idmap *idmap,
 	generic_fillattr(idmap, request_mask, inode, stat);
 
 	orders = shmem_huge_global_enabled(inode, 0, 0, false, NULL, 0);
+	if (!pgtable_has_pmd_leaves())
+		orders &= ~BIT(PMD_ORDER);
 	if (orders)
 		stat->blksize = PAGE_SIZE << highest_order(orders);
 
@@ -4658,8 +4660,7 @@ static int shmem_parse_one(struct fs_context *fc, struct fs_parameter *param)
 	case Opt_huge:
 		ctx->huge = result.uint_32;
 		if (ctx->huge != SHMEM_HUGE_NEVER &&
-		    !(IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
-		      has_transparent_hugepage()))
+		    !IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
 			goto unsupported_parameter;
 		ctx->seen |= SHMEM_SEEN_HUGE;
 		break;
@@ -5451,7 +5452,7 @@ void __init shmem_init(void)
 #endif
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	if (has_transparent_hugepage() && shmem_huge > SHMEM_HUGE_DENY)
+	if (shmem_huge > SHMEM_HUGE_DENY)
 		SHMEM_SB(shm_mnt->mnt_sb)->huge = shmem_huge;
 	else
 		shmem_huge = SHMEM_HUGE_NEVER; /* just in case it was patched */
-- 
2.54.0