Messages in this thread Patch in this message | | | Date | Wed, 16 Aug 2023 21:11:15 +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 2023/8/1 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
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.
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 >>>> + 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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