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SubjectRe: [RFC PATCH linux 2/2] fs/proc: use a hash table for the directory entries
Le 02/10/2014 18:46, Stephen Hemminger a écrit :
> On Thu, 2 Oct 2014 17:25:01 +0200
> Nicolas Dichtel <nicolas.dichtel@6wind.com> wrote:
>
>> From: Thierry Herbelot <thierry.herbelot@6wind.com>
>>
>> The current implementation for the directories in /proc is using a single
>> linked list. This is slow when handling directories with large numbers of
>> entries (eg netdevice-related entries when lots of tunnels are opened).
>>
>> This patch enables multiple linked lists. A hash based on the entry name is
>> used to select the linked list for one given entry.
>>
>> The speed creation of netdevices is faster as shorter linked lists must be
>> scanned when adding a new netdevice.
>>
>> Here are some numbers:
>>
>> dummy30000.batch contains 30 000 times 'link add type dummy'.
>>
>> Before the patch:
>> time ip -b dummy30000.batch
>> real 2m32.221s
>> user 0m0.380s
>> sys 2m30.610s
>>
>> After the patch:
>> time ip -b dummy30000.batch
>> real 1m57.190s
>> user 0m0.350s
>> sys 1m56.120s
>>
>> The single 'subdir' list head is replaced by a subdir hash table. The subdir
>> hash buckets are only allocated for directories. The number of hash buckets
>> is a compile-time parameter.
>>
>> For all functions which handle directory entries, an additional check on the
>> directory nature of the dir entry ensures that pde_hash_buckets was allocated.
>> This check was not needed as subdir was present for all dir entries, whether
>> actual directories or simple files.
>>
>> Signed-off-by: Thierry Herbelot <thierry.herbelot@6wind.com>
>> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
>
> I think the speed up is a good idea and makes sense.
> It would be better to use exist hlist macros for hash table rather than
> open coding it.
>
Right, I will rework this after looking at rbtree.
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