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b=rjRg8MmVMQX/cuud2vWEUG7rlEBs5/1tlb4i2HZuNoDMhuoP68UCCkK5SV72FL/dV q8WwTI+FgGEGLrsiIUPywyExff7RJ/vq4H1hb4mpcCxTpSRanZE7ZItuDvsFQbYcOk tLSknkZYN/ep5ULvx4wtEMv9fruY0RZEMYQRhB8w= Date: Tue, 12 May 2026 15:46:28 -0700 From: Andrew Morton To: Joonwon Kang Cc: dennis@kernel.org, tj@kernel.org, cl@gentwo.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, dodam@google.com Subject: Re: [PATCH v5 4/4] percpu: Fix hint invariant breakage Message-Id: <20260512154628.a30e8eb1827c80e0529b672e@linux-foundation.org> In-Reply-To: <20260510072149.1279887-4-joonwonkang@google.com> References: <20260510072149.1279887-1-joonwonkang@google.com> <20260510072149.1279887-4-joonwonkang@google.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 8F039C0009 X-Rspam-User: X-Stat-Signature: g5cnjwkptmjzu4xjxs71xzgh3aewo87n X-HE-Tag: 1778625990-527794 X-HE-Meta: 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 34lQfjWc zQR4UsgUo5Y0I1uxkApiDIpOgC/KgHLHrBvWcPmUbauPTBMsG8TOZQH7n634D8jIuiEubmXtiOp7wBqaPktgNDz8B/YwFRfeNSy2quuO1eXKv1uU5yW4jqm3oDdjNTCD0Cd8AY4W/vo8jlVGVh/vdXrWu+SwrZDXFsg6p1KlpJeGXg1hjJiXY2qrFkA4nsvZzFedI8geztDITUU1y0Xj4I5JFYFZXI3jNlY/zMES7U3Ea+E4+Hv8jcvixJFDfGejpBz/57CHkfpEjr1/Q9zKkhxsKefTqHCPJUiHJfnJOL5eD+2SDvfb5ew7rVkij5duDtMNHn/OYBB5Dm0o= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, 10 May 2026 07:21:49 +0000 Joonwon Kang wrote: > The invariant "scan_hint_start > contig_hint_start if and only if > scan_hint == contig_hint" should be kept for hint management. However, > it could be broken in some cases: > > - if (new contig == contig_hint == scan_hint) && (contig_hint_start < > scan_hint_start < new contig start) && the new contig is to become a > new contig_hint due to its better alignment, then scan_hint should > be invalidated instead of keeping the old value. > > - if (new contig == contig_hint > scan_hint) && (new contig start < > contig_hint_start) && the new contig is not to become a new > contig_hint, then scan_hint should be not updated to the new contig. > > This commit mainly fixes this invariant breakage and includes more: Thanks. AI review asked a single question: https://sashiko.dev/#/patchset/20260510072149.1279887-1-joonwonkang@google.com