[PATCH RFC 6/8] mm/huge_memory: rearrange split routine handling for better optimization

[Kairui Song via B4 Relay]

From: Kairui Song <kasong@xxxxxxxxxxx>

Anonymous folios never use a mapping or an xarray, so combine the is_anon
and xas conditions into a single if/else-if chain.  The compiler cannot do
this on its own because the xarray split calls sit between the two
conditions and the anon mTHP stat update comes after the split helpers.

./scripts/bloat-o-meter on mm/huge_memory.o (x86-64 KVM test config) shows
__split_frozen_folio() shrinking from 1077 to 996 bytes.

Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
---
 mm/huge_memory.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 7270baa20d80..e16b93318613 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3929,13 +3929,17 @@ static int __split_frozen_folio(struct folio *folio, int new_order,
 	for (split_order = start_order;
 	     split_order >= new_order;
 	     split_order--) {
-		int nr_new_folios = 1UL << (old_order - split_order);
+		if (is_anon) {
+			int nr_new_folios = 1UL << (old_order - split_order);
 
-		/* order-1 anonymous folio is not supported */
-		if (is_anon && split_order == 1)
-			continue;
+			/* order-1 anonymous folio is not supported */
+			if (split_order == 1)
+				continue;
 
-		if (xas) {
+			/* Split can't fail at this point, update counters now */
+			mod_mthp_stat(old_order, MTHP_STAT_NR_ANON, -1);
+			mod_mthp_stat(split_order, MTHP_STAT_NR_ANON, nr_new_folios);
+		} else if (xas) {
 			/*
 			 * uniform split has xas_split_alloc() called before
 			 * irq is disabled to allocate enough memory, whereas
@@ -3960,10 +3964,6 @@ static int __split_frozen_folio(struct folio *folio, int new_order,
 		pgalloc_tag_split(folio, old_order, split_order);
 		__split_folio_to_order(folio, old_order, split_order);
 
-		if (is_anon) {
-			mod_mthp_stat(old_order, MTHP_STAT_NR_ANON, -1);
-			mod_mthp_stat(split_order, MTHP_STAT_NR_ANON, nr_new_folios);
-		}
 		/*
 		 * If uniform split, the process is complete.
 		 * If non-uniform, continue splitting the folio at @split_at

-- 
2.56.1