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

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Message-ID: <aTKDRF2sMdM_5aRB@kernel.org>
Date: Fri, 5 Dec 2025 09:01:24 +0200
From: Mike Rapoport <rppt@...nel.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Shuah Khan <skhan@...uxfoundation.org>, david@...nel.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, Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] Revert "mm: fix MAX_FOLIO_ORDER on powerpc configs with
 hugetlb"

On Thu, Dec 04, 2025 at 01:57:46PM -0800, Andrew Morton wrote:
> On Wed,  3 Dec 2025 19:33:56 -0700 Shuah Khan <skhan@...uxfoundation.org> wrote:
> 
> > This reverts commit 39231e8d6ba7f794b566fd91ebd88c0834a23b98.
> > 
> > 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.
> > 
> > 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
> 
> 39231e8d6ba7 simply shuffles ifdefs and Kconfig items, so I assume it
> exposed a pre-existing bug.
> 
> Reverting 39231e8d6ba7 will re-hide that bug.

Shuah confirmed that the bugs were on v6.18-rc6 and they were fixed in
6.18 [1].

I verified that reverting 39231e8d6ba7 from v6.18-rc6 does not solve
anything, but applying 5bebe8de19264 does [2].

So reverting 39231e8d6ba7 does not change anything and there is no bug it
hides. The bug was introduced by adfb6609c680 ("mm/huge_memory: initialise
the tags of the huge zero folio"), was fixed by 5bebe8de1926
("mm/huge_memory: Fix initialization of huge zero folio") ...

> And that isn't a bad thing.  If we re-hide the bug in 6.18.x and in
> mainline then that relieves the people who are hitting this and it
> takes the pressure off David, Mike and yourself to get the underlying
> bug fixed in a hurry.
> 
> So I think I'll queue this as a hotfix, plan to send it Linuswards in a
> couple of days.
> 
> Or Linus may choose to apply it directly or to do a local revert of
> 39231e8d6ba7.  But I don't see how a local revert will get communicated
> to the 6.18.x maintainers.
> 
> David, Linus, opinions please?
> 
> > Signed-off-by: Shuah Khan <skhan@...uxfoundation.org>
> 
> Let's have a cc:stable here, just to be sure.

... and we can skip all this hassle.

[1] https://lore.kernel.org/all/317deba2-e560-44ed-a9f7-3c6fdc446b6d@linuxfoundation.org
[2] https://lore.kernel.org/linux-mm/aTKAo7JgBX0X_pBl@kernel.org

-- 
Sincerely yours,
Mike.