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Peter Anvin" , Shakeel Butt , Suren Baghdasaryan , Thomas Gleixner , Toshi Kani , Vlastimil Babka , Will Deacon , linux-mm@kvack.org, x86@kernel.org Subject: Re: [PATCH 3/3] x86/mm: Fix and document DEBUG_PAGEALLOC Message-ID: <20260730104333.GE751831@noisy.programming.kicks-ass.net> References: <20260729110807.797920433@infradead.org> <20260729111119.604452135@infradead.org> <20260729144838.GM651302@noisy.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: C108F14000F X-Stat-Signature: 43u4tq3wyznqhexod9gcnzpe4yjkcx5w X-Rspam-User: X-HE-Tag: 1785408224-314500 X-HE-Meta: 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 EmpGbgNB aTs+4C45SvnexIJLmVGhuxTnvigv3OtMOBiuv8XU53wpu7V3lz9kGqc+L9WfZ7c3lcq/kT+hAQXf9AwEGdcdf0qhN15XuJlpKTwWKP5N+oJX/VfDAlQl6GU51AQFfHe5GpNVD0L5da14N4ffIBAPFBDZZhEO7Baa1sHyt8kC4NiCMiT276Xg/XKIg1nunR9i4SRnr50xmHQw9rrDi/aQBfo+adX3zb/wW7XBNs+gyKLrJgIqYD3cKYH5L+rLpAa38+DF1 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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.