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b=XJnsKvWO0+QO80LJM5XIzpjavAEFaK23gF4aRbBGejzwSzWxTVMw1DiDRubaH/zhW DzjVneRMZuMJmYNN4xOxH5C+TyLebDQfGBp2lX4MuuRvggnGNEtGiYgOssQGCOlnvM ax4qJYr/NPXcas8bWv5/dAzJANm6aZ9WGRQm1j5s= Date: Tue, 12 Dec 2023 17:00:48 -0800 From: Andrew Morton To: Matthew Wilcox Cc: Sidhartha Kumar , linux-kernel@vger.kernel.org, linux-mm@kvack.org, maple-tree@lists.infradead.org, liam.howlett@oracle.com, zhangpeng.00@bytedance.com Subject: Re: [PATCH] maple_tree: do not preallocate nodes for slot stores Message-Id: <20231212170048.7c0afab9c0522c7de6067cd7@linux-foundation.org> In-Reply-To: References: <20231212194640.217966-1-sidhartha.kumar@oracle.com> 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-Rspam-User: X-Stat-Signature: c4z9eqk7orijoo7r4cfatocfccu9dmqf X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 793701C0020 X-HE-Tag: 1702429253-949152 X-HE-Meta: U2FsdGVkX1/okUOfuL+2POsgKqYZIrYnMQz9dWupMTnVSYYCm39//bKq9laeMa23yvSl1MSIOSFGU+o+Oq4Nd/CaHVWLjfqJXWm4j6idHE9A9a6p+ri9GLPU/GBz+JxdhYLpwstzKaPOvWcS6MrtS1EkoMciaCj8Qh+Gt52SjR+74vCz0TxwlctGY75FBV9nWlhkfbZgO3ATqll0TAWJioxfFoFIDnAx5dblU/h3bbVRdfi0z8scLwrVhlPY0WLjiTtSFKMSFyKewjYlviyc0eRojxFz8Kx6YeMK9lvrV4I9O0N00/sqOwsdmwvw/Z1lI/pAdmYjMgP5Lim9WpA8zN6jZ6uefn1NZpoj4gRJTM2e9UGjKi+1YLcWsFsYDfi/jan6kE56W7qSQ57Bz8OaW6i8oQ0Rske79nqpmycSZ79kxQPoEZjDLOscQBpoDQJkAYXPI2C3z/OcAMBRH5ewPjwUearQoMQBLvTo/DVAWbTPodQ147SgRTndveO4nnYvr8eO9QYTSF01hvOC1xYqHjXZdHplmmj2tSg/4OOHapzyQ+8+DrBLLvfy9X1hy+LGJsVPyaPsI3DW19rLnIWp8wRi5Yim5cSsvacdTpuuZyFpa4A//dmlIHFz4ma5Gza2geeeNF/cAPm6fKJ2wdudtZOyT1ze4xOpyAlUzn1ag0IOUhsdDIF1GY8EpmxmNSbM8KVU+wVnK9P7vGejPo6DVXmII2UlhRFuggxwvvtG834qxFyqfCSx3j3hB/EVsAFHRM1XQoxlDzTIYxlbzQY5wQpqa53IqthXwDE/R3dv+F5PILe64dNPpYkQo/IdjFpSnd5GHbHkgBxdCEr0Y4XwF2LICiSAHQhYWG3Ps8gEITmmBSrHa19n2JE/T6grQAESr6BjYtq+OuDUWMz/pljRVcXpjncLQR0zdI/3n8fBFy7JqV1gYT1X4uj+WFxjwyp8KlJ3GeA5FZrN0UkRAAZ g6WVWmAR p4DmGPy0sM5s1DuuGb8K2oPwbHBNRQrtweW4tf6uuApckZRDPjbSOLG59VId4MPmFIsVR4pfAhQeWZsS8KxAPykr7xPFMT1leeO5/2W+NsgAve7Uhm8E55QE67zOxRqtiwXbV/x5hFgdkfW2/PXCVQJBTDZFSED+49q8LVawxErP1Nzcvq7hRxE1ggfKPq4APvTmYo2XjUlCnoW4KuCRxkWL4qBcitqd8DDqJtU3ArpT93X1c5r9cd31jHOpLPrRwxNC/5sT1ukKCBRg9PJghz0YKMHoIA4uVt03JQzljEAcseOGxvh3YKzJjioXDU+O154ohYUgTquFfqQ8= 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 Tue, 12 Dec 2023 20:57:48 +0000 Matthew Wilcox wrote: > On Tue, Dec 12, 2023 at 11:46:40AM -0800, Sidhartha Kumar wrote: > > + /* Slot store, does not require additional nodes */ > > + if ((node_size == mas->end) && ((!mt_in_rcu(mas->tree)) > > + || (wr_mas.offset_end - mas->offset == 1))) > > + return 0; > > Should we refactor this into a mas_is_slot_store() predicate? > > A few coding-style problems with it as it's currently written: > > 1. The indentation on the second line is wrong. It makes the > continuation of the condition look like part of the statement. Use > extra whitespace to indent. eg: > > if ((node_size == mas->end) && ((!mt_in_rcu(mas->tree)) > || (wr_mas.offset_end - mas->offset == 1))) > return 0; > > 2. The operator goes last on the line, not at the beginning of the > continuation line. ie: > > if ((node_size == mas->end) && ((!mt_in_rcu(mas->tree)) || > (wr_mas.offset_end - mas->offset == 1))) > return 0; > > 3. You don't need parens around the !mt_in_rcu(mas->tree). There's > no ambiguity to solve here: > > if ((node_size == mas->end) && (!mt_in_rcu(mas->tree) || > (wr_mas.offset_end - mas->offset == 1))) > return 0; > > But I'd write it as: > > if ((node_size == mas->end) && > (!mt_in_rcu(mas->tree) || (wr_mas.offset_end - mas->offset == 1))) > return 0; > > because then the whitespace matches how you're supposed to parse the > condition, and so the next person to read this code will have an easier > time of it. Yup. But I'd suggest going further: /* Slot store, does not require additional nodes */ if (node_size == mas->end) { /* comment goes here */ if (!mt_in_rcu(mas->tree)) return 0; /* and here too */ if (wr_mas.offset_end - mas->offset == 1) return 0; } ie: create space to add those comments explaining the reason for each test.