mm/khugepaged: remove READ_ONLY_THP_FOR_FS check

Patch series "Remove CONFIG_READ_ONLY_THP_FOR_FS and enable file THP for
writable files", v6.

This patch (of 14):

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_folio_support() for FSes supporting
large folio with at least PMD_ORDER.

Link: https://lore.kernel.org/20260517135416.1434539-1-ziy@nvidia.com
Link: https://lore.kernel.org/20260517135416.1434539-2-ziy@nvidia.com
Signed-off-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Nico Pache <npache@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Mason <clm@fb.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Sterba <dsterba@suse.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Liam Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 1f50991b43e3b3b2d0875417103a38498fb1c343..308d846531d030d7df7a4fbb38787da83b996682 100644 (file)
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -513,6 +513,33 @@ static inline bool mapping_large_folio_support(const struct address_space *mappi
        return mapping_max_folio_order(mapping) > 0;
 }
 
+/**
+ * mapping_pmd_folio_support() - Check if a mapping supports PMD-sized folio
+ * @mapping: The address_space
+ *
+ * While some mappings support large folios, they might not support PMD-sized
+ * folios. This function checks whether a mapping supports PMD-sized folios.
+ * For example, khugepaged needs this information before attempting to
+ * collapsing THPs.
+ *
+ * Return: True if PMD-sized folios are supported, otherwise false.
+ */
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static inline bool mapping_pmd_folio_support(const struct address_space *mapping)
+{
+       /* AS_FOLIO_ORDER is only reasonable for pagecache folios */
+       VM_WARN_ON_ONCE((unsigned long)mapping & FOLIO_MAPPING_ANON);
+
+       return mapping_min_folio_order(mapping) <= PMD_ORDER &&
+              mapping_max_folio_order(mapping) >= PMD_ORDER;
+}
+#else
+static inline bool mapping_pmd_folio_support(const struct address_space *mapping)
+{
+       return false;
+}
+#endif
+
 /* 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 33ab5d12e1bc7f280b3e9daf2d8992ea6a708c7d..06be690fe8d2377d7786272395b11bba695c19b9 100644 (file)
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2246,8 +2246,14 @@ 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
+        *
+        * TODO: once shmem always calls mapping_set_large_folios() on its
+        * mapping, the shmem check can be removed.
+        */
+       VM_WARN_ON_ONCE(!is_shmem && !mapping_pmd_folio_support(mapping));
+       VM_WARN_ON_ONCE(start & (HPAGE_PMD_NR - 1));
 
        result = alloc_charge_folio(&new_folio, mm, cc, HPAGE_PMD_ORDER);
        if (result != SCAN_SUCCEED)