[PATCH v4 5/6] mm: shmem: add mTHP size alignment in shmem_get_unmapped_area

[Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>]

Although the top-level hugepage allocation can be turned off, anonymous shmem
can still use mTHP by configuring the sysfs interface located at
'/sys/kernel/mm/transparent_hugepage/hugepage-XXkb/shmem_enabled'. Therefore,
add alignment for mTHP size to provide a suitable alignment address in
shmem_get_unmapped_area().

Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Tested-by: Lance Yang <ioworker0@xxxxxxxxx>
---
 mm/shmem.c | 40 +++++++++++++++++++++++++++++++---------
 1 file changed, 31 insertions(+), 9 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 9a8533482208..2ecc41521dbb 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2394,6 +2394,7 @@ unsigned long shmem_get_unmapped_area(struct file *file,
 	unsigned long inflated_len;
 	unsigned long inflated_addr;
 	unsigned long inflated_offset;
+	unsigned long hpage_size;
 
 	if (len > TASK_SIZE)
 		return -ENOMEM;
@@ -2412,8 +2413,6 @@ unsigned long shmem_get_unmapped_area(struct file *file,
 
 	if (shmem_huge == SHMEM_HUGE_DENY)
 		return addr;
-	if (len < HPAGE_PMD_SIZE)
-		return addr;
 	if (flags & MAP_FIXED)
 		return addr;
 	/*
@@ -2425,8 +2424,11 @@ unsigned long shmem_get_unmapped_area(struct file *file,
 	if (uaddr == addr)
 		return addr;
 
+	hpage_size = HPAGE_PMD_SIZE;
 	if (shmem_huge != SHMEM_HUGE_FORCE) {
 		struct super_block *sb;
+		unsigned long __maybe_unused hpage_orders;
+		int order = 0;
 
 		if (file) {
 			VM_BUG_ON(file->f_op != &shmem_file_operations);
@@ -2439,18 +2441,38 @@ unsigned long shmem_get_unmapped_area(struct file *file,
 			if (IS_ERR(shm_mnt))
 				return addr;
 			sb = shm_mnt->mnt_sb;
+
+			/*
+			 * Find the highest mTHP order used for anonymous shmem to
+			 * provide a suitable alignment address.
+			 */
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+			hpage_orders = READ_ONCE(huge_anon_shmem_orders_always);
+			hpage_orders |= READ_ONCE(huge_anon_shmem_orders_within_size);
+			hpage_orders |= READ_ONCE(huge_anon_shmem_orders_madvise);
+			if (SHMEM_SB(sb)->huge != SHMEM_HUGE_NEVER)
+				hpage_orders |= READ_ONCE(huge_anon_shmem_orders_inherit);
+
+			if (hpage_orders > 0) {
+				order = highest_order(hpage_orders);
+				hpage_size = PAGE_SIZE << order;
+			}
+#endif
 		}
-		if (SHMEM_SB(sb)->huge == SHMEM_HUGE_NEVER)
+		if (SHMEM_SB(sb)->huge == SHMEM_HUGE_NEVER && !order)
 			return addr;
 	}
 
-	offset = (pgoff << PAGE_SHIFT) & (HPAGE_PMD_SIZE-1);
-	if (offset && offset + len < 2 * HPAGE_PMD_SIZE)
+	if (len < hpage_size)
+		return addr;
+
+	offset = (pgoff << PAGE_SHIFT) & (hpage_size - 1);
+	if (offset && offset + len < 2 * hpage_size)
 		return addr;
-	if ((addr & (HPAGE_PMD_SIZE-1)) == offset)
+	if ((addr & (hpage_size - 1)) == offset)
 		return addr;
 
-	inflated_len = len + HPAGE_PMD_SIZE - PAGE_SIZE;
+	inflated_len = len + hpage_size - PAGE_SIZE;
 	if (inflated_len > TASK_SIZE)
 		return addr;
 	if (inflated_len < len)
@@ -2463,10 +2485,10 @@ unsigned long shmem_get_unmapped_area(struct file *file,
 	if (inflated_addr & ~PAGE_MASK)
 		return addr;
 
-	inflated_offset = inflated_addr & (HPAGE_PMD_SIZE-1);
+	inflated_offset = inflated_addr & (hpage_size - 1);
 	inflated_addr += offset - inflated_offset;
 	if (inflated_offset > offset)
-		inflated_addr += HPAGE_PMD_SIZE;
+		inflated_addr += hpage_size;
 
 	if (inflated_addr > TASK_SIZE - len)
 		return addr;
-- 
2.39.3