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b=OsQN2JztTjwkSYM58ujeukp87a4ECEkelesp8ge0DINPmvZSy5h/p1xe4h9mURfSv FQiqDNxLHR4XatBx12+aIJ0QPxbZlpILve6PDnMXpemSMLwq91AIpoPya0owAU45WA b9ZaFNFNdB7wMxMhO0pbZYH7WY269Sbd9PMrOpEA= Date: Mon, 15 Sep 2025 20:52:24 -0700 From: Andrew Morton To: SeongJae Park Cc: Joshua Hahn , damon@lists.linux.dev, kernel-team@meta.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 1/6] mm/damon/core: reset age if nr_accesses changes between non-zero and zero Message-Id: <20250915205224.aa2de8de6dad1bb4c048cec8@linux-foundation.org> In-Reply-To: <20250915182652.110173-1-sj@kernel.org> References: <20250915145158.1425390-1-joshua.hahnjy@gmail.com> <20250915182652.110173-1-sj@kernel.org> X-Mailer: Sylpheed 3.8.0beta1 (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-Queue-Id: 67B54140002 X-Stat-Signature: j75hnzhkg9o443kgwwad35m7hyxd5tjn X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1757994746-551468 X-HE-Meta: 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 j3H5I+Jw 6s0/hDMsBOAkeiOTSL7eaD+NYzdl6whSwmlrEIUUuQJR+oVyI9AiBMwrFGJBPoXKNY/AEopLfJS310ILHCMRznc8GzuE/HIl0IuNO9wJfOFY1mLLVOC+xL9JQzFJbJNtMxbo9KHQOgN4xegto9CZsnz6IRM2OrPxtzG4ELvjlTg6JBSl61inB4jW+nML9ndccIKpTlpycMHjKX/1y6u2BAIMgecVIVfYZXVa/YdqFdoPbXBT4YGp87HfJgUMz2kyEmt5+QpOeCm7S1sOWyKH78SeJeVdiN38S+LvyGJG+dA52B+HV9E1xsn1zIjbblaH7RwTOe3VP+NgK4Eqlz9f8stPMe/OPzybjzAR4e5lXpf/ADd6p9XGaIURyMqbEWTsSlrZdT58s3s4oz9s= 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 Mon, 15 Sep 2025 11:26:51 -0700 SeongJae Park wrote: > > Thank you for the patch, I think the goal of the patch makes sesne to me. > > I have a small nit / idea which I think makes the code a bit clearer, at least > > for me. It seems that we basically want to XOR the two values's zero-ness, so > > maybe something like > > > > (!!r->nr_accesses) ^ (!!r->last_nr_access) or > > (r->nr_accesses == 0) ^ (r->last_nr_access == 0) > > > > Can achieve the goal? > > Thank you for the idea, this makes sense! > > > I know bitwise operations are sometimes harder to > > understand, so I am just throwing the idea out there : -) > > To be honest I'm one of people who are not familiar with XOR. I had to spend a > minute to understand the above. Maybe we can replace '^' with '!=', and it is > easier to read for me. If you don't mind, I will use below in the next > version: > > else if ((r->nr_accesses == 0) != (r->last_nr_accesses == 0)) > > Please let me know if I'm missing something or you have other opinions. I have to say, using xor as a shorthand for what-was-really-intended always bursts my brain. I have to stop, think about it and mentally turn the implementation back into what-was-really-intended. Maybe that's just me. Ditto less-than-utterly-trivial :? expressions. Perhaps it's because if-then-else best suits how our minds work.