From: Max Kellermann <max.kellermann@ionos.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: david@redhat.com, lorenzo.stoakes@oracle.com, ziy@nvidia.com,
baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com,
npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com,
baohua@kernel.org, shikemeng@huaweicloud.com,
kasong@tencent.com, nphamcs@gmail.com, bhe@redhat.com,
chrisl@kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] huge_mm.h: disallow is_huge_zero_folio(NULL)
Date: Thu, 28 Aug 2025 07:17:35 +0200 [thread overview]
Message-ID: <CAKPOu+_EfTBxh7xpaRdypD-hnqAbgj-bSdMTZE4uafqMudxBRg@mail.gmail.com> (raw)
In-Reply-To: <20250827165309.44e465ff214e45f1a6665b24@linux-foundation.org>
On Thu, Aug 28, 2025 at 1:53 AM Andrew Morton <akpm@linux-foundation.org> wrote:
> OK, but it remains the case that we have seen code which calls
> is_huge_zero_folio() prior to the initialization of huge_zero_folio.
>
> Is this a bug? I think so. Should we be checking for recurrences of
> this bug?
Why do you believe it's a bug? To me, as a newbie here, such a call
seems perfectly fine; please explain.
> Also, sigh. I do dislike seeing VM_WARN_ON_ONCE() in an inline
> function - heaven knows how much bloat that adds. Defconfig
> mm/huge_memory.o (which has three calls) grows by 80 bytes so I guess
> that's livable with.
Oh, how is this possible? defconfig has CONFIG_DEBUG_VM=n and that
means VM_WARN_ON_ONCE() is just BUILD_BUG_ON_INVALID() which should
generate no code at all.
Here on my computer (aarch64 with GCC 14), the size (and the
disassembly) is exactly the same. This confirms what David Hildenbrand
predicted.
Are you seeing some compiler weirdness, maybe?
next prev parent reply other threads:[~2025-08-28 5:17 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-08-26 23:16 [PATCH 1/2] huge_mm.h: is_huge_zero_folio(NULL) should return false Max Kellermann
2025-08-26 23:16 ` [PATCH 2/2] mm/swap: add BUG_ON(folio==NULL) to folios_put_refs() Max Kellermann
2025-08-27 1:42 ` Zi Yan
2025-08-27 2:12 ` Chris Li
2025-08-27 9:38 ` David Hildenbrand
2025-08-27 1:19 ` [PATCH 1/2] huge_mm.h: is_huge_zero_folio(NULL) should return false Zi Yan
2025-08-27 1:55 ` Andrew Morton
2025-08-27 4:39 ` Max Kellermann
2025-08-27 9:36 ` David Hildenbrand
2025-08-27 10:13 ` Max Kellermann
2025-08-27 11:56 ` David Hildenbrand
2025-08-27 13:06 ` Max Kellermann
2025-08-27 14:34 ` David Hildenbrand
2025-08-27 15:03 ` [PATCH v2] huge_mm.h: disallow is_huge_zero_folio(NULL) Max Kellermann
2025-08-27 15:16 ` Lorenzo Stoakes
2025-08-27 15:38 ` Max Kellermann
2025-08-27 20:01 ` David Hildenbrand
2025-08-27 20:26 ` David Hildenbrand
2025-08-27 20:44 ` Lorenzo Stoakes
2025-08-28 8:48 ` [PATCH v3] " Max Kellermann
2025-08-28 9:35 ` Lorenzo Stoakes
2025-08-29 1:25 ` Zi Yan
2025-08-27 23:53 ` [PATCH v2] " Andrew Morton
2025-08-28 5:17 ` Max Kellermann [this message]
2025-08-28 7:57 ` David Hildenbrand
2025-08-27 15:05 ` [PATCH 1/2] huge_mm.h: is_huge_zero_folio(NULL) should return false Max Kellermann
2025-08-27 9:35 ` David Hildenbrand
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