Re: [PATCH v5 01/14] mm/khugepaged: remove READ_ONLY_THP_FOR_FS check

[Zi Yan]

On 7 May 2026, at 14:08, Zi Yan wrote:

> On 29 Apr 2026, at 23:29, 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_folio_support() for FSes supporting large
>> folio with at least PMD_ORDER.
>>
>> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
>> Reviewed-by: Lance Yang <lance.yang@xxxxxxxxx>
>> Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
>> ---
>>  include/linux/pagemap.h | 26 ++++++++++++++++++++++++++
>>  mm/khugepaged.c         | 10 ++++++++--
>>  2 files changed, 34 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
>> index 1f50991b43e3b..1fed3414fe9b8 100644
>> --- a/include/linux/pagemap.h
>> +++ b/include/linux/pagemap.h
>> @@ -513,6 +513,32 @@ 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 support PMD-sized folio
>> + * @mapping: The address_space
>> + *
>> + * Some file supports large folio but does not support as large as PMD order.
>> + * If a PMD-sized pagecache folio is attempted to be created on a filesystem,
>> + * this check needs to be performed first.
>> + *
>> + * Return: true - PMD-sized folio is supported, false - PMD-sized folio is not
>> + * supported.
>> + */
>> +#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_max_folio_order(mapping) >= PMD_ORDER;
>
> Hi Andrew,
>
> Can you help apply the fixup below? It addresses the concern raised by
> Nico and Lance[1]. Thanks.
>
> [1] https://lore.kernel.org/all/aa778cfc-b7f8-4100-89bb-d2b2ef8e1138@xxxxxxxxxx/
>

I was missing a semicolon. Here is the right fixup. Sorry for the noise.

From fbd183f7528a3d0bdb421018af4aef45f6366682 Mon Sep 17 00:00:00 2001
From: Zi Yan <ziy@xxxxxxxxxx>
Date: Thu, 7 May 2026 02:02:28 -0400
Subject: [PATCH] fix mapping_pmd_folio_support() to represent its exact
 meaning.

Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
---
 include/linux/pagemap.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index c6a4ecd3d6ed1..41dbb55a47d8e 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -530,7 +530,8 @@ 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_max_folio_order(mapping) >= PMD_ORDER;
+	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)
-- 
2.53.0




Best Regards,
Yan, Zi