* Peng Zhang <zhangpeng.00@xxxxxxxxxxxxx> [230731 08:39]: > > > 在 2023/7/27 00:08, Liam R. Howlett 写道: > > * Peng Zhang <zhangpeng.00@xxxxxxxxxxxxx> [230726 04:10]: > > > If mas has located a specific entry, it may be need to replace this > > > entry, so introduce mas_replace_entry() to do this. mas_replace_entry() > > > will be more efficient than mas_store*() because it doesn't do many > > > unnecessary checks. > > > > > > This function should be inline, but more functions need to be moved to > > > the header file, so I didn't do it for the time being. > > > > I am really nervous having no checks here. I get that this could be > > used for duplicating the tree more efficiently, but having a function > > that just swaps a value in is very dangerous - especially since it is > > decoupled from the tree duplication code. > I've thought about this, and I feel like this is something the user > should be guaranteed. If the user is not sure whether to use it, > mas_store() can be used instead. Documentation often isn't up to date and even more rarely read. mas_replace_entry() does not give a hint of a requirement for a specific state to the mas. This is not acceptable. The description of the function also doesn't say anything about a requirement of the maple state, just that it replaces an already existing entry. You have to read the notes to find out that 'mas must already locate an existing entry'. >And we should provide this interface > because it has better performance. How much better is the performance? There's always a trade off but without numbers, this is hard to justify. > > > > > > > > Signed-off-by: Peng Zhang <zhangpeng.00@xxxxxxxxxxxxx> > > > --- > > > include/linux/maple_tree.h | 1 + > > > lib/maple_tree.c | 25 +++++++++++++++++++++++++ > > > 2 files changed, 26 insertions(+) > > > > > > diff --git a/include/linux/maple_tree.h b/include/linux/maple_tree.h > > > index 229fe78e4c89..a05e9827d761 100644 > > > --- a/include/linux/maple_tree.h > > > +++ b/include/linux/maple_tree.h > > > @@ -462,6 +462,7 @@ struct ma_wr_state { > > > void *mas_walk(struct ma_state *mas); > > > void *mas_store(struct ma_state *mas, void *entry); > > > +void mas_replace_entry(struct ma_state *mas, void *entry); > > > void *mas_erase(struct ma_state *mas); > > > int mas_store_gfp(struct ma_state *mas, void *entry, gfp_t gfp); > > > void mas_store_prealloc(struct ma_state *mas, void *entry); > > > diff --git a/lib/maple_tree.c b/lib/maple_tree.c > > > index efac6761ae37..d58572666a00 100644 > > > --- a/lib/maple_tree.c > > > +++ b/lib/maple_tree.c > > > @@ -5600,6 +5600,31 @@ void *mas_store(struct ma_state *mas, void *entry) > > > } > > > EXPORT_SYMBOL_GPL(mas_store); > > > +/** > > > + * mas_replace_entry() - Replace an entry that already exists in the maple tree > > > + * @mas: The maple state > > > + * @entry: The entry to store > > > + * > > > + * Please note that mas must already locate an existing entry, and the new entry > > > + * must not be NULL. If these two points cannot be guaranteed, please use > > > + * mas_store*() instead, otherwise it will cause an internal error in the maple > > > + * tree. This function does not need to allocate memory, so it must succeed. > > > + */ > > > +void mas_replace_entry(struct ma_state *mas, void *entry) > > > +{ > > > + void __rcu **slots; > > > + > > > +#ifdef CONFIG_DEBUG_MAPLE_TREE > > > + MAS_WARN_ON(mas, !mte_is_leaf(mas->node)); > > > + MAS_WARN_ON(mas, !entry); > > > + MAS_WARN_ON(mas, mas->offset >= mt_slots[mte_node_type(mas->node)]); > > > +#endif > > > + > > > + slots = ma_slots(mte_to_node(mas->node), mte_node_type(mas->node)); > > > + rcu_assign_pointer(slots[mas->offset], entry); > > > +} > > > +EXPORT_SYMBOL_GPL(mas_replace_entry); > > > + > > > /** > > > * mas_store_gfp() - Store a value into the tree. > > > * @mas: The maple state > > > -- > > > 2.20.1 > > >