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Howlett" Cc: SeongJae Park , Andrew Morton , maple-tree@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Suren Baghdasaryan , Matthew Wilcox , Sidhartha Kumar , Vlastimil Babka , Alice Ryhl , Kuninori Morimoto , Geert Uytterhoeven , Arnd Bergmann , Christian Kujau Subject: Re: [PATCH v3 21/30] maple_tree: Add cp_is_new_root() helper Date: Mon, 2 Feb 2026 09:53:53 -0800 Message-ID: <20260202175354.39717-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: pekuu3egisgspizqaf9kz5j4oypnt5qw X-Rspamd-Queue-Id: 388781C000C X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1770054837-43705 X-HE-Meta: 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 qHu310k/ pgaElyRm7TAbUhmvZZCTgIBx3PDfqSY8uR/89oWa7a4ZE019uF1ZI/FDC0FHAU0lKxtSWYyKUfTMrl2YGtKndWZz3lLZ3IHSLvotMnv8/zoQS8FaJJuQBZtl1fKhEIjOkE0U2sIqsMG0abLiHt0z/dFQ9uHPPCFoa3w9XVPztNYPI/HZJfV4gIpqyP4oBo9tTGTOzvQD+arBAEKBq3lg746bZ1KHaXe603SVKY5E+6N960iCejWQ7tgi1AdKYb96GMTH9CtfyX1L5Tr0tK/mH8c7ZPh7rI8F1sFE76PXTDrwOZqSXvU1dkyERbQ== 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, 2 Feb 2026 12:01:53 -0500 "Liam R. Howlett" wrote: > * SeongJae Park [260202 10:56]: > > On Mon, 2 Feb 2026 09:58:31 -0500 "Liam R. Howlett" wrote: > > > > > * SeongJae Park [260131 19:10]: > > > > Hello, > > > > > > > > On Fri, 30 Jan 2026 15:59:26 -0500 "Liam R. Howlett" wrote: > > > > > > > > > Add a helper to do what is needed when the maple copy node contains a > > > > > new root node. This is useful for future commits and is > > > > > self-documenting code. > > > > > > > > > > Signed-off-by: Liam R. Howlett > > > > > --- > > > > > lib/maple_tree.c | 70 ++++++++++++++++++++++++++---------------------- > > > > > 1 file changed, 38 insertions(+), 32 deletions(-) > > > > > > > > > > diff --git a/lib/maple_tree.c b/lib/maple_tree.c > > > > > index 5280fa6d2d6ec..42038e42a4c7e 100644 > > > > > --- a/lib/maple_tree.c > > > > > +++ b/lib/maple_tree.c > > > > > @@ -3337,6 +3337,43 @@ static void mas_spanning_rebalance(struct ma_state *mas, > > > > > mas_spanning_rebalance_loop(mas, mast, count); > > > > > } > > > > > > > > > > +static inline bool cp_is_new_root(struct maple_copy *cp, struct ma_state *mas) > > > > > +{ > > > > > + if (cp->min || cp->max != ULONG_MAX) > > > > > + return false; > > > > > + > > > > > + if (cp->d_count != 1) { > > > > > + enum maple_type mt = maple_arange_64; > > > > > + > > > > > + if (!mt_is_alloc(mas->tree)) > > > > > + mt = maple_range_64; > > > > > + > > > > > + cp->data = cp->d_count; > > > > > + cp->s_count = 0; > > > > > + dst_setup(cp, mas, mt); > > > > > + init_cp_src(cp); > > > > > + node_copy(mas, cp->src[0].node, 0, cp->data, cp->max, maple_copy, > > > > > + cp->dst[0].node, 0, mt); > > > > > + node_finalise(cp->dst[0].node, mt, cp->end + 1); > > > > > + /* > > > > > + * Warning, see cp_leaf_init() comment and rcu_assign_pointer() > > > > > + * documentation. Since this is a new root, there are no > > > > > + * read-side operations that can view it until it is insert into > > > > > + * the tree after an rcu_assign_pointer() call. > > > > > + */ > > > > > + RCU_INIT_POINTER(cp->slot[0], mt_mk_node(cp->dst[0].node, mt)); > > > > > > > > I just found the above makes my build test using an old version compiler fails. > > > > Fortunately, seems it is same to the one we discussed before [1], and same > > > > mitigation like below attached patch works, at least for my test setup. > > > > > > Thanks SJ. > > > > My pleasure :) > > > > > > > > This is still with gcc 8.1.0? > > > > Yes. The test code is available at GitHub [1]. > > > > Nonetheless, another test [2] that is using 9.3.0 was also failing. > > You have two failures: one in 8.1 and one in 9.3? Yes. FYI, I picked the compiler versions for no good reason but just because there were reports of DAMON build failures on the compilers in the past. > > I was planning to test 7.5.0 and ensure everything works, but this > implies my plan will not catch everything? >From Documentation/process/changes.rst, I find minimal version of GCC for building kernel is 8.1. So gcc 7.5.0 might not need to be ensured for? I have no good expertise on planning tests, though. Thanks, SJ [...]