[PATCH] mm: shmem: fix too little space for tmpfs only fallback 4KB

[Vernon Yang <vernon2gm@gmail.com>]

From: Vernon Yang <yanglincheng@kylinos.cn>

When the system memory is sufficient, allocating memory is always
successful, but when tmpfs size is low (e.g. 1MB), it falls back
directly from 2MB to 4KB, and other small granularity (8KB ~ 1024KB)
will not be tried.

Therefore add check whether the remaining space of tmpfs is sufficient
for allocation. If there is too little space left, try smaller large
folio.

Fixes: acd7ccb284b8 ("mm: shmem: add large folio support for tmpfs")
Signed-off-by: Vernon Yang <yanglincheng@kylinos.cn>
---
 mm/shmem.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/mm/shmem.c b/mm/shmem.c
index 8c592c6db2a0..b20affd57b23 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1820,6 +1820,7 @@ static unsigned long shmem_suitable_orders(struct inode *inode, struct vm_fault
 					   unsigned long orders)
 {
 	struct vm_area_struct *vma = vmf ? vmf->vma : NULL;
+	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
 	pgoff_t aligned_index;
 	unsigned long pages;
 	int order;
@@ -1835,6 +1836,18 @@ static unsigned long shmem_suitable_orders(struct inode *inode, struct vm_fault
 	while (orders) {
 		pages = 1UL << order;
 		aligned_index = round_down(index, pages);
+
+		/*
+		 * Check whether the remaining space of tmpfs is sufficient for
+		 * allocation. If there is too little space left, try smaller
+		 * large folio.
+		 */
+		if (sbinfo->max_blocks && percpu_counter_read(&sbinfo->used_blocks)
+						+ pages > sbinfo->max_blocks) {
+			order = next_order(&orders, order);
+			continue;
+		}
+
 		/*
 		 * Check for conflict before waiting on a huge allocation.
 		 * Conflict might be that a huge page has just been allocated
-- 
2.51.0