Messages in this thread | | | Date | Fri, 18 Aug 2023 17:39:53 +0800 | Subject | Re: [PATCH 06/11] maple_tree: Introduce mas_replace_entry() to directly replace an entry | From | Peng Zhang <> |
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在 2023/8/17 01:40, Liam R. Howlett 写道: > * Peng Zhang <zhangpeng.00@bytedance.com> [230816 09:11]: >> >> >> 在 2023/8/1 00:48, Liam R. Howlett 写道: >>> * 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. >> I have implemented a new version of this pachset, and I will post it >> soon. >> >> I tested the benefits of mas_replace_entry() in userspace. >> The test code is attached at the end. >> >> Run three times: >> mas_replace_entry(): 2.7613050s 2.7120030s 2.7274200s >> mas_store(): 3.8451260s 3.8113200s 3.9334160s > > This runtime is too short, we should increase the number of elements or > loops until it is over 10 seconds. This will make the setup time > and other variances less significant and we can use the command run time > as a rough estimate of performance. IIRC 134 was picked for a rough > estimate of an average task size so maybe increase the loops. I changed nr_entries to 1000, and the measured numbers are as follows: mas_replace_entry(): 20.0375820s mas_store(): 28.6175720s It can be seen that mas_store() is still nearly 40% slower. > > I understand the numbers here are from clock recordings to demonstrate > the significance of your change. > >> >> Using mas_store() reduces the performance of duplicating VMAs by about >> 41%. >> >> So I think mas_replace_entry() is necessary. We can describe it in more >> detail in the documentation to prevent users from misusing it. > > I think something is necessary for a quicker replacement, yes. I don't > want to go as far as you did with the lack of checking. > >> >> >> static noinline void __init bench_forking(struct maple_tree *mt) >> { >> struct maple_tree newmt; >> int i, nr_entries = 134, nr_fork = 80000, ret; >> void *val; >> MA_STATE(mas, mt, 0, 0); >> MA_STATE(newmas, &newmt, 0, 0); >> clock_t start; >> clock_t end; >> double cpu_time_used = 0; >> >> for (i = 0; i <= nr_entries; i++) >> mtree_store_range(mt, i*10, i*10 + 5, >> xa_mk_value(i), GFP_KERNEL); >> >> for (i = 0; i < nr_fork; i++) { >> mt_set_non_kernel(99999); >> >> start = clock(); >> mt_init_flags(&newmt, MT_FLAGS_ALLOC_RANGE); >> mas_lock(&newmas); >> mas_lock(&mas); >> ret = __mt_dup(mt, &newmt, GFP_NOWAIT | __GFP_NOWARN); >> if (ret) { >> pr_err("OOM!"); >> BUG_ON(1); >> } >> >> mas_set(&newmas, 0); >> mas_for_each(&newmas, val, ULONG_MAX) { >> mas_replace_entry(&newmas, val); >> } >> >> mas_unlock(&mas); >> mas_unlock(&newmas); >> end = clock(); >> cpu_time_used += ((double) (end - start)); >> >> mas_destroy(&newmas); >> mt_validate(&newmt); >> mt_set_non_kernel(0); >> mtree_destroy(&newmt); >> } >> printf("time consumption:%.7fs\n", cpu_time_used / CLOCKS_PER_SEC); >> } >> >> >>> >>>>> >>>>>> >>>>>> 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 > > CONFIG_DEBUG_MAPLE_TREE is not necessary, MAS_WRAN_ON() will be compiled > out if it's not set. > >>>>>> + 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 >>>>>>
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