PATCH : talloc-2.0.1 to add support for static talloc pools

[Karthick A R]

Hi Matthias,

On Tue, Jan 18, 2011 at 11:21 PM, Matthias Dieter Wallnöfer
<mdw at samba.org>wrote:

> Hi Kathick,
>
> small question to your patch:
>
>> +static inline int talloc_pool_map_get(struct talloc_chunk *tc)
>> +{
>> +    unsigned int *map = TALLOC_POOL_MAP(tc);
>> +    unsigned int count = *talloc_cache_objectcount(tc);
>> +    unsigned int map_words = TALLOC_POOL_MAP_WORDS(count);
>> +    static int ffz_map[16] = { 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1,
>> 0, -1 };
>> +    int i;
>> +    for(i = 0; i<  map_words; ++i) {
>> +        unsigned int offset = 0;
>> +        unsigned int mask = map[i]&  0xffffffffU;
>> +        if(mask == 0xffffffffU) continue;
>>
>>
> Why is "i" signed here? Is it since "talloc_pool_map_get" returns "-1" on
> error conditions?
>

Yes.


> I would transform "i" to unsigned and return it like this: return (int) i;
>
> Sure. Will do. Let me know if these changes are a candidate for talloc and
I would update and send probably a final patch with the review feedback.

Regards,
-Karthick


>
> Karthick A R wrote:
>
>> Hi,
>>  Please find attached a patch that would apply clean on top of talloc
>> 2.0.1
>> that adds support for static talloc pools.
>>  I introduced a simple talloc static pool which creates a static pool of
>> fixed object sizes for a reclaimable object cache.
>>  The current talloc_pool is a variable sized pool where frees just
>> decrement
>> the object count which is good if one wants to preallocate a large pool
>> for
>> faster allocations.
>>  But I thought of adding another api that allows us to create a fixed size
>> cache. When all allocations are granted, it would fail instead of falling
>> back to malloc.(like the current pool)
>>
>>  This enables one to create a talloc pool cache and then just use the
>> context pointer to allocate fixed size objects from the
>>  pre-created static cache. Because its a fixed-size pool cache, it
>> supports
>> freeing objects to the pool as well.
>>  Allocations and free from the static pool add a bitmap overhead to keep
>> track of objects allocations and frees.
>>  But the existing talloc_pool header overhead remains unchanged. The
>> following apis were added:
>>
>> +void *talloc_pool_cache(const void *context, size_t size, size_t
>> objsize);
>> +void *talloc_cache(const void *context);
>> +void *talloc_cache_zero(const void *context);
>>
>> talloc_cache just passed the context and expects to grab the static object
>> size for the pool. I haven't added any overhead to the talloc_chunk struct
>> as well to avoid impacting the current use-case on top of the
>> talloc_pools.
>> A new TALLOC_FLAG_POOLCACHE has been added to track the allocations to the
>> static pool. This adds an extra bit the flag bit and hence also adjusts
>> the
>> talloc magic base which currently has a 4 bit flag space accordingly.
>>
>> Apart from the api additions, I have also fixed a crash when trying to use
>> nested talloc pools as currently that tries to free(tc) in case the tc or
>> the pool itself was allocated from another parent pool.
>>
>> Eg:
>>    void *poolfoo = talloc_pool(parent, sizeof(struct foo) * 1024);
>>    void *poolbar = talloc_pool(poolfoo, sizeof(struct bar) * 100); /*
>> subpool*/
>>
>> Trying to talloc_free(poolbar) would cause a crash currently. The patch
>> also
>> addresses this by trying to trace the parent of the subpool to free the
>> subpool to the parent pool context.
>>
>> Alternatively I have also forked the talloc 2.0.1 code base with the above
>> changes at my github repo:
>> https://github.com/karthick18/talloc
>>
>> You can also trace the diff over 2.0.1 here :
>>
>> https://github.com/karthick18/talloc/commit/d19bf7d298c276e38b988d00234ca8a8606db6e3
>>
>> <
>> https://github.com/karthick18/talloc/commit/d19bf7d298c276e38b988d00234ca8a8606db6e3
>> >A
>> simple usage eg: for talloc in general which also includes usage for the
>> newly added apis can be traced here:
>> https://github.com/karthick18/talloc/blob/master/talloc_test.c
>>
>> If you guys are ok with the patch, then maybe I can patch it on top of the
>> latest 2.0.5 talloc. This won't be required to get into Samba talloc
>> anyway
>> but might be a good candidate to consider for the standalone LGPL
>> super-COOL
>> talloc!
>>
>> Regards,
>> -Karthick
>>
>> <https://github.com/karthick18/talloc/blob/master/talloc_test.c>
>>
>>
>
>


-- 
-- 
Software is like sex: it's better when it's free.
-Linus Torvalds

A.R.Karthick
http://github.com/karthick18