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Fri, 20 Jan 2023 08:26:15 -0800 (PST) Date: Fri, 20 Jan 2023 11:27:12 -0500 From: Johannes Weiner To: Brian Foster Cc: Nhat Pham , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, willy@infradead.org, linux-api@vger.kernel.org, kernel-team@meta.com, Yu Zhao Subject: Re: [PATCH v6 1/3] workingset: refactor LRU refault to expose refault recency check Message-ID: References: <20230117195959.29768-1-nphamcs@gmail.com> <20230117195959.29768-2-nphamcs@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 33E8D16000E X-Stat-Signature: yh517765oi4hfzhxak9bj6uywrqgfezh X-Rspam-User: X-HE-Tag: 1674231976-234093 X-HE-Meta: U2FsdGVkX18lG3y95PhvgXH2Gaad8myGtak3wq7GB9fbQea+wKa0Rx3wzFhakWrBBNqWYEYuOWIdHXoufpOv+Xae+FUtHyHNGpX4D20GWfo/9O5OY93C+8h8gZCQO15VdRao06lzCAEONYSIAcNc+QC7N/DgLRG+wR/2Q8UFEyDmlMWNvkXInJKiJ7vPeJtdvGj6C+R8EhFMYWytnUZp/Pj7rnDCl2OdeEOAsQMzFWi+kDXCVbaKcke0RXNyp7NKT6vJRauxDB0oHCpbFW/a6pGnd5q/Uakh6Spzjc4GL4vDUgxABdOIKcvqXjqqhd9f2BDGXJ2jc4zFznkBwfi2Adnxmb/drwUttVQMfWzowOdO/RKgRdINhIa1X4627D21G+MqhFLv6yJp0GukxtGzqUDW3OIo9JhqkSsJq2nr3/dsNQcSJb/1YI4EJiruYuLrhrzi4jSNNBGBfZUw32at772eqStMW/tKi0wsXTJp/Xofyp2+bADnSBHGB/dGD65lcuBByVeopmNCWVjlSGZb2WN/c8Y018cRu3aPDHbvOx08HP5sRLk7n+4eY82QBto2GAg3LKLtSLdxPoYTFY0XM3LtngGN9c6HIJ6VhDo1fDpvGjVLqntXRdXT2GCIgaZjt7cPufOaOjawApGgLYRSI/So8wDHWdpWQp/JT/owv5xfykMmiB4SGuPl+8D7wiqul/h5EqnBHfq5s643yXc7ASc2Iw++zrFcHPqjxfRJ6/Pe75ay0Cen3UfJzn7j7MPydMpAVCqhM6Te8cXY1juvoAfFm4zHRaSsTjNhFOSOAZaW7o2nCX8b7k6ULHmqLkqxpquEntZ4y7QFx+/0a7DVUMdSF4u1cPHrkxsMYuQSIhccbQeSQBDBezs4HhP7+RYQoOUZrGVC2T8Umu4/e34B8OqImZsgcLjN529dejUS5mTo41vEwG8J2ViIYtXtYPSujL/U3i2VcgRgYa/xkoz oYfb8vvD 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000007, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Jan 20, 2023 at 09:34:18AM -0500, Brian Foster wrote: > On Tue, Jan 17, 2023 at 11:59:57AM -0800, Nhat Pham wrote: > > + int memcgid; > > + struct pglist_data *pgdat; > > + unsigned long token; > > + > > + unpack_shadow(shadow, &memcgid, &pgdat, &token, workingset); > > + eviction_memcg = mem_cgroup_from_id(memcgid); > > + > > + lruvec = mem_cgroup_lruvec(eviction_memcg, pgdat); > > + lrugen = &lruvec->lrugen; > > + > > + min_seq = READ_ONCE(lrugen->min_seq[file]); > > + return !((token >> LRU_REFS_WIDTH) != (min_seq & (EVICTION_MASK >> LRU_REFS_WIDTH))); > > I think this might be more readable without the double negative. > > Also it looks like this logic is pulled from lru_gen_refault(). Any > reason the caller isn't refactored to use this helper, similar to how > workingset_refault() is modified? It seems like a potential landmine to > duplicate the logic here for cachestat purposes and somewhere else for > actual workingset management. The initial version was refactored. Yu explicitly requested it be duplicated [1] to cut down on some boiler plate. I have to agree with Brian on this one, though. The factored version is better for maintenance than duplicating the core logic here. Even if it ends up a bit more boiler plate - it's harder to screw that up, and easier to catch at compile time, than the duplicates diverging. [1] https://lore.kernel.org/lkml/CAOUHufZKTqoD2rFwrX9-eCknBmeWqP88rZ7X7A_5KHHbGBUP=A@mail.gmail.com/