From: Peter Zijlstra <peterz@infradead.org>
To: Mike Rapoport <rppt@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
linux-kernel@vger.kernel.org, Andy Lutomirski <luto@kernel.org>,
Borislav Petkov <bp@alien8.de>,
David Hildenbrand <david@kernel.org>,
Ingo Molnar <mingo@redhat.com>, Jason Gunthorpe <jgg@ziepe.ca>,
Juergen Gross <jgross@suse.com>,
Kevin Tian <kevin.tian@intel.com>,
Kiryl Shutsemau <kas@kernel.org>,
"Liam R. Howlett" <liam@infradead.org>,
Lorenzo Stoakes <ljs@kernel.org>,
Lu Baolu <baolu.lu@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Shakeel Butt <shakeel.butt@linux.dev>,
Suren Baghdasaryan <surenb@google.com>,
Thomas Gleixner <tglx@kernel.org>,
Toshi Kani <toshi.kani@hpe.com>,
Vlastimil Babka <vbabka@kernel.org>,
Will Deacon <will@kernel.org>,
linux-mm@kvack.org, x86@kernel.org
Subject: Re: [PATCH 3/3] x86/mm: Fix and document DEBUG_PAGEALLOC
Date: Thu, 30 Jul 2026 12:43:33 +0200 [thread overview]
Message-ID: <20260730104333.GE751831@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <ampPb0o0T_JdxrMx@kernel.org>
On Wed, Jul 29, 2026 at 10:07:27PM +0300, Mike Rapoport wrote:
> > > I like my version with your comments added there more as it localizes the
> > > DEBUG_PAGEALLOC exception in the lock wrappers.
> >
> > So I don't like removing cpa_lock entirely; it is still serializing cpa
>
> I meant static inline cpa_lock(), not removing it entirely.
> With your comment why DEBUG_PAGEALLOC is special.
That is, I despise the whole:
if (!debug_pagealloc_enabled())
spin_lock(&cpa_lock);
with a passion. It blanked kills cpa_lock as whole and changes the rules
for everyone when debug_pagealloc is on.
cpa_lock ensures that concurrent cpa() calls on an overlapping region
have a well defined outcome. By removing it entirely you can get random
state.
In practise this isn't likely to matter, but relaxing this for a debug
option is insane. Debug stuff should tighten rules, not relax them.
next prev parent reply other threads:[~2026-07-30 10:43 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-29 11:08 [PATCH 0/3] x86/mm: DEBUG_PAGEALLOC musings Peter Zijlstra
2026-07-29 11:08 ` [PATCH 1/3] x86/mm: Use guard() in cpa_collapse_large_pages() Peter Zijlstra
2026-07-29 11:08 ` [PATCH 2/3] x86/mm: Use guard() for pgd_lock Peter Zijlstra
2026-07-29 11:08 ` [PATCH 3/3] x86/mm: Fix and document DEBUG_PAGEALLOC Peter Zijlstra
2026-07-29 14:13 ` Mike Rapoport
2026-07-29 14:48 ` Peter Zijlstra
2026-07-29 19:07 ` Mike Rapoport
2026-07-30 10:43 ` Peter Zijlstra [this message]
2026-07-30 11:17 ` Mike Rapoport
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