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Message-ID: <205f093a-8b43-5b3b-7e87-2dcbe434f519@oracle.com>
Date:   Tue, 10 Oct 2023 17:17:06 -0700
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Subject: Re: [PATCH 2/3] maple_tree: use preallocations in mas_store_gfp()
To:     Peng Zhang <zhangpeng.00@bytedance.com>
Cc:     akpm@linux-foundation.org, willy@infradead.org,
        liam.howlett@oracle.com, linux-kernel@vger.kernel.org,
        maple-tree@lists.infradead.org, linux-mm@kvack.org
References: <20231009201639.920512-1-sidhartha.kumar@oracle.com>
 <20231009201639.920512-3-sidhartha.kumar@oracle.com>
 <d6182b74-5879-4e5a-8605-abd55542215d@bytedance.com>
Content-Language: en-US
From:   Sidhartha Kumar <sidhartha.kumar@oracle.com>
In-Reply-To: <d6182b74-5879-4e5a-8605-abd55542215d@bytedance.com>
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On 10/9/23 8:03 PM, Peng Zhang wrote:
> Hi,
> 
> 在 2023/10/10 04:16, Sidhartha Kumar 写道:
>> Preallocate maple nodes before call to mas_wr_store_entry(). If a new
>> node is not needed, go directly to mas_wr_store_entry(), otherwise
>> allocate the needed nodes and set the MA_STATE_PREALLOC flag.
>>
>> Signed-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
>> ---
>>   lib/maple_tree.c | 22 +++++++++++++++++++---
>>   1 file changed, 19 insertions(+), 3 deletions(-)
>>
>> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
>> index e239197a57fc..25ae66e585f4 100644
>> --- a/lib/maple_tree.c
>> +++ b/lib/maple_tree.c
>> @@ -5478,17 +5478,33 @@ int mas_prealloc_calc(struct ma_wr_state *wr_mas)
>>   int mas_store_gfp(struct ma_state *mas, void *entry, gfp_t gfp)
>>   {
>>       MA_WR_STATE(wr_mas, mas, entry);
>> +    int request;
>>       mas_wr_store_setup(&wr_mas);
>> -    trace_ma_write(__func__, mas, 0, entry);
>> -retry:
>> +    wr_mas.content = mas_start(mas);
>> +
>> +    request = mas_prealloc_calc(&wr_mas);
> mas_wr_store_entry() does something similar to mas_prealloc_calc().
> Now, making it do it twice would incur additional overhead.
> We encountered this issue while optimizing preallocation, but it
> hasn't been resolved yet. Previously, this problem only occurred
> when using mas_preallocate(). Now, this change would bring this
> impact to all write operations on maple tree. What do you think
> about it?
> 

After talking to Liam, I will have to implement the store type enum 
feature on the Maple Tree Work list so that mas_prealloc_calc() can 
start a partial walk and write that information to the enum. 
mas_wr_store_entry() can then read that enum to continue the walk that 
was already started rather than having to redo the whole walk. This 
could also be used in mas_preallocate(). Do you have any suggestions for 
the implementation of this enum?

Thanks,
Sid

> Thanks,
> Peng
>> +    if (!request)
>> +        goto store_entry;
>> +
>> +    mas_node_count_gfp(mas, request, gfp);
>> +    if (unlikely(mas_is_err(mas))) {
>> +        mas_set_alloc_req(mas, 0);
>> +        mas_destroy(mas);
>> +        mas_reset(mas);
>> +        return xa_err(mas->node);
>> +    }
>> +    mas->mas_flags |= MA_STATE_PREALLOC;
>> +
>> +store_entry:
>>       mas_wr_store_entry(&wr_mas);
>>       if (unlikely(mas_nomem(mas, gfp)))
>> -        goto retry;
>> +        goto store_entry;
>>       if (unlikely(mas_is_err(mas)))
>>           return xa_err(mas->node);
>> +    trace_ma_write(__func__, mas, 0, entry);
>>       return 0;
>>   }
>>   EXPORT_SYMBOL_GPL(mas_store_gfp);
>