linux-kernel - Re: [PATCH] Revert "mm: fix MAX_FOLIO_ORDER on powerpc configs with hugetlb"

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Message-ID: <78af7da4-d213-42c6-8ca6-c2bdca81f233@linuxfoundation.org>
Date: Thu, 4 Dec 2025 10:03:09 -0700
From: Shuah Khan <skhan@...uxfoundation.org>
To: Mike Rapoport <rppt@...nel.org>,
 "David Hildenbrand (Red Hat)" <david@...nel.org>
Cc: akpm@...ux-foundation.org, maddy@...ux.ibm.com, mpe@...erman.id.au,
 npiggin@...il.com, christophe.leroy@...roup.eu, lorenzo.stoakes@...cle.com,
 Liam.Howlett@...cle.com, vbabka@...e.cz, surenb@...gle.com, mhocko@...e.com,
 masahiroy@...nel.org, linuxppc-dev@...ts.ozlabs.org,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH] Revert "mm: fix MAX_FOLIO_ORDER on powerpc configs with
 hugetlb"

On 12/3/25 23:35, Mike Rapoport wrote:
> On Thu, Dec 04, 2025 at 07:17:06AM +0100, David Hildenbrand (Red Hat) wrote:
>> Hi,
>>
>> On 12/4/25 03:33, Shuah Khan wrote:
>>> This reverts commit 39231e8d6ba7f794b566fd91ebd88c0834a23b98.
>>
>> That was supposed to fix powerpc handling though. So I think we have to
>> understand what is happening here.

This patch changes include/linux/mm.h and mm/Kconfig in addition to
arch/powerpc/Kconfig and arch/powerpc/platforms/Kconfig.cputype

With this patch HAVE_GIGANTIC_FOLIOS is enabled on x86_64 config

The following mm/Kconfig isn't arch specific. This makes this
not powerpc specific and this is enabled on x86_64

+#
+# We can end up creating gigantic folio.
+#
+config HAVE_GIGANTIC_FOLIOS
+       def_bool (HUGETLB_PAGE && ARCH_HAS_GIGANTIC_PAGE) || \
+                (ZONE_DEVICE && HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
+

The following change in include/linux/mm.h is also generic
and applies to x86_64 as well.

-#if !defined(CONFIG_ARCH_HAS_GIGANTIC_PAGE)
+#if !defined(CONFIG_HAVE_GIGANTIC_FOLIOS)

Is this not intended on all architectures?

>>
>>>
>>> Enabling HAVE_GIGANTIC_FOLIOS broke kernel build and git clone on two
>>> systems. git fetch-pack fails when cloning large repos and make hangs
>>> or errors out of Makefile.build with Error: 139. These failures are
>>> random with git clone failing after fetching 1% of the objects, and
>>> make hangs while compiling random files.
>>
>> On which architecture do we see these issues and with which kernel configs?
>> Can you share one?

Config attached.

>>
>>>
>>> The blow is is one of the git clone failures:
>>>
>>> git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git linux_6.19
>>> Cloning into 'linux_6.19'...
>>> remote: Enumerating objects: 11173575, done.
>>> remote: Counting objects: 100% (785/785), done.
>>> remote: Compressing objects: 100% (373/373), done.
>>> remote: Total 11173575 (delta 534), reused 505 (delta 411), pack-reused 11172790 (from 1)
>>> Receiving objects: 100% (11173575/11173575), 3.00 GiB | 7.08 MiB/s, done.
>>> Resolving deltas: 100% (9195212/9195212), done.
>>> fatal: did not receive expected object 0002003e951b5057c16de5a39140abcbf6e44e50
>>> fatal: fetch-pack: invalid index-pack output
>>
>> If I would have to guess, these symptoms match what we saw between commit
>> adfb6609c680 ("mm/huge_memory: initialise the tags of the huge zero folio")
>> and commit 5bebe8de1926 ("mm/huge_memory: Fix initialization of huge zero folio").
>>
>> 5bebe8de1926 went into v6.18-rc7.
>>
>> Just to be sure, are you sure we were able to reproduce this issue with a
>> v6.18-rc7 or even v6.18 that contains 5bebe8de1926?
>>
>> Bisecting might give you wrong results, as the problems of adfb6609c680 do not
>> reproduce reliably.
>   
> I can confirm that bisecting gives odd results between v6.18-rc5 and
> v6.18-rc6. I was seeing failures in some tests, bisected a few times and
> got a bunch of bogus commits including 3470715e5c22 ("MAINTAINERS: update
> David Hildenbrand's email address") :)

I am sure this patch is the cause oh the problems I have seen on my two
systems. Reverting this commit solved issues since this commit does
impact all architectures enabling HAVE_GIGANTIC_FOLIOS if the conditions
are right.

> 
> And 5bebe8de1926 actually solved the issue for me.

Were you seeing the problems I reported without 5bebe8de1926?
Is 5bebe8de1926 is 6.18?

I can try this commit with 39231e8d6ba7f794b566fd91ebd88c0834a23b98
and see what happens on my system.

thanks,
-- Shuah

View attachment "config_6.18" of type "text/plain" (220419 bytes)