[question] how to increase the number of object on cache?

[question] how to increase the number of object on cache?

[Shawn Joo]

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Dear Experts,

I would like to know a mechanism, how to increase the number of object and where the memory is from.

(because when cache is created by "kmem_cache_create", there is only object size, but no number of the object)
For example, "size-65536" does not have available memory from below dump.
In that state, if memory allocation is requested to "size-65536",

1.     How to allocate/increase the number of object on "size-65536"?

2.     Where is the new allocated memory from? (from buddy?)

I believe it is hard to explain with simple word, any advice will be very helpful.

cat /proc/buddyinfo
Node 0, zone   Normal    949      0      0      2      3      3      0      0      1      1      0

cat /proc/slabinfo
slabinfo - version: 2.1
# name            <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab> : tunables <limit> <batchcount> <sharedfactor> : slabdata <active_slabs> <num_slabs> <sharedavail>
size-4194304           0      0 4194304    1 1024 : tunables    1    1    0 : slabdata      0      0      0
size-2097152           0      0 2097152    1  512 : tunables    1    1    0 : slabdata      0      0      0
size-1048576           0      0 1048576    1  256 : tunables    1    1    0 : slabdata      0      0      0
size-524288            0      0 524288    1  128 : tunables    1    1    0 : slabdata      0      0      0
size-262144            0      0 262144    1   64 : tunables    1    1    0 : slabdata      0      0      0
size-131072            1      1 131072    1   32 : tunables    8    4    0 : slabdata      1      1      0
size-65536             4      4  65536    1   16 : tunables    8    4    0 : slabdata      4      4      0




Thanks,
Seongho(Shawn)


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Re: [question] how to increase the number of object on cache?

[Glauber Costa]

On 08/02/2012 04:20 PM, Shawn Joo wrote:
> Dear Experts,
> 
>  
> 
> I would like to know a mechanism, how to increase the number of object
> and where the memory is from.
> 
> (because when cache is created by "kmem_cache_create", there is only
> object size, but no number of the object)
> 
> For example, “size-65536” does not have available memory from below dump.
> 
> In that state, if memory allocation is requested to “size-65536”,
> 
> 1.     How to allocate/increase the number of object on “size-65536”?
> 
> 2.     Where is the new allocated memory from? (from buddy?)
> 
>  

I am not sure I fully understand your question. But if you refer to
something like "from where does the object allocators get their memory
when more is needed", then yes, they will allocate the necessary number
of pages from the standard page allocator.

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RE: [question] how to increase the number of object on cache?

[Shawn Joo]

>> then yes, they will allocate the necessary number of pages from the standard page allocator.
Who is "the standard page allocator" for cache in /proc/slabinfo, e.g. "size-65536" ?
I believe one of allocator is buddy. who else?

Thanks,
Seongho(Shawn)


-----Original Message-----
From: Glauber Costa [mailto:glommer@parallels.com] 
Sent: Thursday, August 02, 2012 9:51 PM
To: Shawn Joo
Cc: cl@linux-foundation.org; penberg@kernel.org; mpm@selenic.com; linux-mm@kvack.org
Subject: Re: [question] how to increase the number of object on cache?

On 08/02/2012 04:20 PM, Shawn Joo wrote:
> Dear Experts,
> 
>  
> 
> I would like to know a mechanism, how to increase the number of object 
> and where the memory is from.
> 
> (because when cache is created by "kmem_cache_create", there is only 
> object size, but no number of the object)
> 
> For example, "size-65536" does not have available memory from below dump.
> 
> In that state, if memory allocation is requested to "size-65536",
> 
> 1.     How to allocate/increase the number of object on "size-65536"?
> 
> 2.     Where is the new allocated memory from? (from buddy?)
> 
>  

I am not sure I fully understand your question. But if you refer to something like "from where does the object allocators get their memory when more is needed", then yes, they will allocate the necessary number of pages from the standard page allocator.

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-----------------------------------------------------------------------------------

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Re: [question] how to increase the number of object on cache?

[Glauber Costa]

On 08/02/2012 04:55 PM, Shawn Joo wrote:
>>> then yes, they will allocate the necessary number of pages from the standard page allocator.
> Who is "the standard page allocator" for cache in /proc/slabinfo, e.g. "size-65536" ?
> I believe one of allocator is buddy. who else?
> 
The generic and algorithm-neutral answer to this is "whoever would
handle alloc_pages()".
In the specific case, yes, this is the buddy allocator.

Take a look at mm/slab.c, for instance:

When a cache can't service an allocation, it does:

  cache_grow()
  -> kmem_getpages()
    -> alloc_pages_exact_node()


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Re: [question] how to increase the number of object on cache?

[Michal Hocko]

On Thu 02-08-12 20:20:25, Shawn Joo wrote:
> Dear Experts,
> 
> I would like to know a mechanism, how to increase the number of object and where the memory is from.
> 
> (because when cache is created by "kmem_cache_create", there is only object size, but no number of the object)
> For example, "size-65536" does not have available memory from below dump.
> In that state, if memory allocation is requested to "size-65536",

Is this a follow up for
http://www.spinics.net/lists/linux-mm/msg39252.html? It would be better
to follow the thread in that case.

> 1.     How to allocate/increase the number of object on "size-65536"?

Object count is increased automatically and transparently for the cache
users. Why would you want to control its size from the outside?

> 2.     Where is the new allocated memory from? (from buddy?)

page allocator when it cannot find any room in the internally available
space. Have a look at [1] if you want to learn more about the slab
allocator (the code has changed since then but the princibles are still
valid).

[1] http://kernel.org/doc/gorman/html/understand/understand011.html

-- 
Michal Hocko
SUSE Labs

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Re: [question] how to increase the number of object on cache?

[Christoph Lameter]

On Thu, 2 Aug 2012, Shawn Joo wrote:

> 1.     How to allocate/increase the number of object on "size-65536"?

I would suggest to use the page allocator directly for large allocations
like this. The slab allocators specialize in cutting 4k pages up in
smaller units and serving those units effectively.

> 2.     Where is the new allocated memory from? (from buddy?)

Ultimately yes but the slab allocators may have their own caching layer on
top given the slow as molasses page allocator. The caching effect is
excellent for small objects but not for large objects such as yours.

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