From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>
To: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: avagin@gmail.com, npiggin@gmail.com,
mathieu.desnoyers@efficios.com, peterz@infradead.org,
michael.christie@oracle.com, surenb@google.com,
brauner@kernel.org, willy@infradead.org,
akpm@linux-foundation.org, corbet@lwn.net,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-mm@kvack.org, linux-doc@vger.kernel.org
Subject: Re: [PATCH 06/11] maple_tree: Introduce mas_replace_entry() to directly replace an entry
Date: Mon, 31 Jul 2023 12:48:54 -0400 [thread overview]
Message-ID: <20230731164854.vbndc2z2mqpw53in@revolver> (raw)
In-Reply-To: <20aab1af-c183-db94-90d7-5e5425e3fd80@bytedance.com>
* Peng Zhang <zhangpeng.00@bytedance.com> [230731 08:39]:
>
>
> 在 2023/7/27 00:08, Liam R. Howlett 写道:
> > * Peng Zhang <zhangpeng.00@bytedance.com> [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@bytedance.com>
> > > ---
> > > 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
> > >
next prev parent reply other threads:[~2023-07-31 16:49 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-26 8:09 [PATCH 00/11] Introduce mt_dup() to improve the performance of fork() Peng Zhang
2023-07-26 8:09 ` [PATCH 01/11] maple_tree: Introduce ma_nonleaf_data_end{_nocheck}() Peng Zhang
2023-07-26 14:58 ` Liam R. Howlett
2023-07-31 9:52 ` Peng Zhang
2023-07-31 16:08 ` Liam R. Howlett
2023-07-26 8:09 ` [PATCH 02/11] maple_tree: Validate MAPLE_ENODE and ma_nonleaf_data_end() Peng Zhang
2023-07-26 8:09 ` [PATCH 03/11] maple_tree: Add some helper functions Peng Zhang
2023-07-26 15:02 ` Liam R. Howlett
2023-07-26 15:08 ` Matthew Wilcox
2023-07-31 11:45 ` Peng Zhang
2023-08-11 17:28 ` Liam R. Howlett
2023-07-31 11:40 ` Peng Zhang
2023-07-26 8:09 ` [PATCH 04/11] maple_tree: Introduce interfaces __mt_dup() and mt_dup() Peng Zhang
2023-07-26 16:03 ` Liam R. Howlett
2023-07-31 12:24 ` Peng Zhang
2023-07-31 16:27 ` Liam R. Howlett
2023-08-16 13:41 ` Peng Zhang
2023-08-16 18:30 ` Liam R. Howlett
2023-08-18 11:53 ` Peng Zhang
2023-08-18 16:13 ` Liam R. Howlett
2023-07-26 8:09 ` [PATCH 05/11] maple_tree: Add test for mt_dup() Peng Zhang
2023-07-26 16:06 ` Liam R. Howlett
2023-07-31 12:32 ` Peng Zhang
2023-07-31 16:41 ` Liam R. Howlett
2023-07-26 8:09 ` [PATCH 06/11] maple_tree: Introduce mas_replace_entry() to directly replace an entry Peng Zhang
2023-07-26 16:08 ` Liam R. Howlett
2023-07-31 12:39 ` Peng Zhang
2023-07-31 16:48 ` Liam R. Howlett [this message]
2023-08-16 13:11 ` Peng Zhang
2023-08-16 17:40 ` Liam R. Howlett
2023-08-18 9:39 ` Peng Zhang
2023-08-18 16:15 ` Liam R. Howlett
2023-07-26 8:09 ` [PATCH 07/11] maple_tree: Update the documentation of maple tree Peng Zhang
2023-07-26 8:09 ` [PATCH 08/11] maple_tree: Skip other tests when BENCH is enabled Peng Zhang
2023-07-26 8:09 ` [PATCH 09/11] maple_tree: Update check_forking() and bench_forking() Peng Zhang
2023-07-26 8:09 ` [PATCH 10/11] MAINTAINERS: Add co-maintainer for maple tree Peng Zhang
2023-07-26 16:39 ` Liam R. Howlett
2023-07-31 12:55 ` Peng Zhang
2023-07-31 20:55 ` Liam R. Howlett
2023-07-26 8:09 ` [PATCH 11/11] fork: Use __mt_dup() to duplicate maple tree in dup_mmap() Peng Zhang
2023-07-26 17:06 ` Liam R. Howlett
2023-07-31 12:59 ` Peng Zhang
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