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Howlett" , Brendan Jackman , David Hildenbrand , Lorenzo Stoakes , Michal Hocko , Mike Rapoport , Suren Baghdasaryan , Vlastimil Babka , Zi Yan , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel-team@meta.com Subject: Re: [PATCH v2 1/4] mm/page_alloc/vmstat: Simplify refresh_cpu_vm_stats change detection Date: Fri, 26 Sep 2025 11:33:43 -0700 Message-Id: <20250926183343.54956-1-sj@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250926182438.3108364-1-joshua.hahnjy@gmail.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: F25C21A000E X-Stat-Signature: nhedokyub6t91rnz8geuugupyx1go4rm X-Rspam-User: X-HE-Tag: 1758911626-633032 X-HE-Meta: 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 ajwFPefw RSBwo7U0+d074WTaZ0A5cMGU6JraEmRR3kMxaLMadseuvkMnEvRLKHz8UKj0zHV93r3JrMWogHgVwIw01Cj4ta4pNqolRyiFHr0KTU3dVpIfmL2p7cLJbyr+5775V/Ac3QugeNXVTlZuVqB490BMvWiVdeDtOOK0GdVnCEYu5eLYIOjtz+B3hDZ7dOGTnSsvDTRygfHpHDX9Fr4ZzGvZBFH6M1b8FzIb76pEOMp+4dhLkD5MwQCIAO3Q+1UoMVcK9BFM87Cy5OlWYGspDXnurcaoORMu7Rkt8PiDHlVJXPs3VcCwA/FPkc9B45ZMQjjdB2FEt X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 26 Sep 2025 11:24:37 -0700 Joshua Hahn wrote: [...] > > > @@ -839,7 +839,7 @@ static int refresh_cpu_vm_stats(bool do_pagesets) > > > if (do_pagesets) { > > > cond_resched(); > > > > > > - changes += decay_pcp_high(zone, this_cpu_ptr(pcp)); > > > + changed |= decay_pcp_high(zone, this_cpu_ptr(pcp)); > > > > I'm not a fan of bit operations unless it provides clear benefits. > > What about below? > > > > if (decay_pcp_high(zone, this_cpu_ptr(pcp)) && !changed) > > changed = truee; > > Here, what if I change it to just: > > if (decay_pcp_high(zone, this_cpu_ptr(pcp)) > changed = true; Looks nice to me! :) > > Since even if changed == true already, this will be a no-op. I was thinking the compiler might or might not emit unnecessary writes, but I don't really care that. Your suggested version looks good to me :) > > > Just a personal and trivial taste. No strong opinion. If you don't strongly > > feel my suggestion is better, please keep the original code. > > I feel like if someone (you) feels like bitwise operations here makes it > less clear what the code is doing, others may feel the same way as well! > Happy to make the change to hopefully make it more easily understandable > what is happening. Thank you Joshua! [...] > Thanks SJ, I hope you have a great day! You too! Plus, great weekend! Thanks, SJ [...]