linux-kernel - [PATCH 2/2] mm: shmem: disallow hugepages if the system-wide shmem THP sysfs settings are disabled

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Message-ID: <c1a6fe55f668cfe87ad113faa49120f049ba9cb5.1748506520.git.baolin.wang@linux.alibaba.com>
Date: Thu, 29 May 2025 16:23:55 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: akpm@...ux-foundation.org,
	hughd@...gle.com,
	david@...hat.com
Cc: lorenzo.stoakes@...cle.com,
	Liam.Howlett@...cle.com,
	npache@...hat.com,
	ryan.roberts@....com,
	dev.jain@....com,
	ziy@...dia.com,
	baolin.wang@...ux.alibaba.com,
	linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] mm: shmem: disallow hugepages if the system-wide shmem THP sysfs settings are disabled

The MADV_COLLAPSE will ignore the system-wide shmem THP sysfs settings, which
means that even though we have disabled the shmem THP configuration, MADV_COLLAPSE
will still attempt to collapse into a shmem THP. This violates the rule we have
agreed upon: never means never.

Then the current strategy is:
For shmem, if none of always, madvise, within_size, and inherit have enabled
PMD-sized mTHP, then MADV_COLLAPSE will be prohibited from collapsing PMD-sized mTHP.

For tmpfs, if the mount option is set with the 'huge=never' parameter, then
MADV_COLLAPSE will be prohibited from collapsing PMD-sized mTHP.

Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
---
 mm/huge_memory.c |  2 +-
 mm/shmem.c       | 12 ++++++------
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index d3e66136e41a..a8cfa37cae72 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -166,7 +166,7 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,
 	 * own flags.
 	 */
 	if (!in_pf && shmem_file(vma->vm_file))
-		return shmem_allowable_huge_orders(file_inode(vma->vm_file),
+		return orders & shmem_allowable_huge_orders(file_inode(vma->vm_file),
 						   vma, vma->vm_pgoff, 0,
 						   !enforce_sysfs);
 
diff --git a/mm/shmem.c b/mm/shmem.c
index 4b42419ce6b2..4dbb28d85cd9 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -613,7 +613,7 @@ static unsigned int shmem_get_orders_within_size(struct inode *inode,
 }
 
 static unsigned int shmem_huge_global_enabled(struct inode *inode, pgoff_t index,
-					      loff_t write_end, bool shmem_huge_force,
+					      loff_t write_end,
 					      struct vm_area_struct *vma,
 					      unsigned long vm_flags)
 {
@@ -625,7 +625,7 @@ static unsigned int shmem_huge_global_enabled(struct inode *inode, pgoff_t index
 		return 0;
 	if (shmem_huge == SHMEM_HUGE_DENY)
 		return 0;
-	if (shmem_huge_force || shmem_huge == SHMEM_HUGE_FORCE)
+	if (shmem_huge == SHMEM_HUGE_FORCE)
 		return maybe_pmd_order;
 
 	/*
@@ -860,7 +860,7 @@ static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo,
 }
 
 static unsigned int shmem_huge_global_enabled(struct inode *inode, pgoff_t index,
-					      loff_t write_end, bool shmem_huge_force,
+					      loff_t write_end,
 					      struct vm_area_struct *vma,
 					      unsigned long vm_flags)
 {
@@ -1261,7 +1261,7 @@ static int shmem_getattr(struct mnt_idmap *idmap,
 			STATX_ATTR_NODUMP);
 	generic_fillattr(idmap, request_mask, inode, stat);
 
-	if (shmem_huge_global_enabled(inode, 0, 0, false, NULL, 0))
+	if (shmem_huge_global_enabled(inode, 0, 0, NULL, 0))
 		stat->blksize = HPAGE_PMD_SIZE;
 
 	if (request_mask & STATX_BTIME) {
@@ -1768,7 +1768,7 @@ unsigned long shmem_allowable_huge_orders(struct inode *inode,
 		return 0;
 
 	global_orders = shmem_huge_global_enabled(inode, index, write_end,
-						  shmem_huge_force, vma, vm_flags);
+						  vma, vm_flags);
 	/* Tmpfs huge pages allocation */
 	if (!vma || !vma_is_anon_shmem(vma))
 		return global_orders;
@@ -1790,7 +1790,7 @@ unsigned long shmem_allowable_huge_orders(struct inode *inode,
 	/* Allow mTHP that will be fully within i_size. */
 	mask |= shmem_get_orders_within_size(inode, within_size_orders, index, 0);
 
-	if (vm_flags & VM_HUGEPAGE)
+	if (shmem_huge_force || (vm_flags & VM_HUGEPAGE))
 		mask |= READ_ONCE(huge_shmem_orders_madvise);
 
 	if (global_orders > 0)
-- 
2.43.5