On 2026/4/23 10:51, Zi Yan wrote:
On 22 Apr 2026, at 22:43, Lance Yang wrote:
On Fri, Apr 17, 2026 at 10:44:18PM -0400, Zi Yan wrote:
collapse_file() requires FSes supporting large folio with at least
PMD_ORDER, so replace the READ_ONLY_THP_FOR_FS check with that.
MADV_COLLAPSE ignores shmem huge config, so exclude the check for shmem.
While at it, replace VM_BUG_ON with VM_WARN_ON_ONCE.
Add a helper function mapping_pmd_thp_support() for FSes supporting large
folio with at least PMD_ORDER.
Signed-off-by: Zi Yan <[email protected]>
---
include/linux/pagemap.h | 10 ++++++++++
mm/khugepaged.c | 5 +++--
2 files changed, 13 insertions(+), 2 deletions(-)
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index ec442af3f886..c3cb1ec982cd 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -524,6 +524,16 @@ static inline bool mapping_large_folio_support(const
struct address_space *mappi
return mapping_max_folio_order(mapping) > 0;
}
+static inline bool mapping_pmd_thp_support(const struct address_space *mapping)
+{
+ /* AS_FOLIO_ORDER is only reasonable for pagecache folios */
+ VM_WARN_ONCE((unsigned long)mapping & FOLIO_MAPPING_ANON,
+ "Anonymous mapping always supports PMD THP");
Nit: afraid not, at least when running on architectures without PMD leaf
entries ...
Maybe better to say this helper is only meaningful for pagecache-backed
mappings. Anonymous mappings should not reach here.
Good suggestion. Will fix it.
+
+ return mapping_max_folio_order(mapping) >= PMD_ORDER;
+}
+
+
/* Return the maximum folio size for this pagecache mapping, in bytes. */
static inline size_t mapping_max_folio_size(const struct address_space *mapping)
{
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index b8452dbdb043..3eb5d982d3d3 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1892,8 +1892,9 @@ static enum scan_result collapse_file(struct mm_struct
*mm, unsigned long addr,
int nr_none = 0;
bool is_shmem = shmem_file(file);
- VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
- VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
+ /* MADV_COLLAPSE ignores shmem huge config, so do not check shmem */
+ VM_WARN_ON_ONCE(!is_shmem && !mapping_pmd_thp_support(mapping));
With [1], can we drop !is_shmem here as well? shmem would then always
call mapping_set_large_folios(inode->i_mapping):
---8<---
diff --git a/mm/shmem.c b/mm/shmem.c
index 4ecefe02881d..dafbea53b22d 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -3087,10 +3087,7 @@ static struct inode *__shmem_get_inode(struct mnt_idmap
*idmap,
cache_no_acl(inode);
if (sbinfo->noswap)
mapping_set_unevictable(inode->i_mapping);
-
- /* Don't consider 'deny' for emergencies and 'force' for testing */
- if (sbinfo->huge)
- mapping_set_large_folios(inode->i_mapping);
+ mapping_set_large_folios(inode->i_mapping);
switch (mode & S_IFMT) {
default:
--
But we can do that in a follow-up, once the revert lands :)
Right. That would make this patchset depend on Baolin’s fix. A follow-up
patch is easier for managing these patches. I will add a TODO in the
comment, so that we will not forget. Thank you for the suggestion.
OK. With the changes above,
Reviewed-by: Lance Yang <[email protected]>
