Not Initialize the shrinker->list after kmalloc() in mm/vmscan.c(V2.6.12)?

Not Initialize the shrinker->list after kmalloc() in mm/vmscan.c(V2.6.12)?

[qingxiaoming]

Dear all:
I am reading the function set_shrinker() in mm/vmscan.c of V2.6.12, and I
have a question about the not initialization of list_head,

/*
 * Add a shrinker callback to be called from the vm
 */
struct shrinker *set_shrinker(int seeks, shrinker_t theshrinker)
{
        struct shrinker *shrinker;

        shrinker = kmalloc(sizeof(*shrinker), GFP_KERNEL);
        if (shrinker) {
	        shrinker->shrinker = theshrinker;
	        shrinker->seeks = seeks;
	        shrinker->nr = 0;
	        down_write(&shrinker_rwsem);
	        list_add_tail(&shrinker->list, &shrinker_list);
	        up_write(&shrinker_rwsem);
	}
	return shrinker;
}

As above, the shrinker is allocated from kmalloc, coming from slab
allocator,the list in shrinker is not initialized, directly list_add_tail()
to shrinker_list, don't need to INIT_LIST_HEAD(shrinker->list)?

Thanks,
Best Regards!
Xiaoming.Qing

Why is Linux not RTOS?

[Rick Brown]

Hi,

Why is Linux kernel considered a (hard) realtime OS? I already
understand the basic reason is that the linux kernel does not
guarantee that a task will be completed on time. But I would
appreciate answers in terms of more of kernel jargons.

What stops us from classifying kernel as hard RTOS? Is it because at
times the kernel is non-preemptive (for e.g. while holding spinlocks)?
Has it got something to do with interrupt latency / scheduling latency
etc?

Is the behaviour of the kernel (when it is preemptive) similar to hard
real time OS ??

Thanks,

Rick
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Not Initialize the shrinker->list after kmalloc() in mm/vmscan.c(V2.6.12)?

[qingxiaoming]

Dear all:
I am reading the function set_shrinker() in mm/vmscan.c of V2.6.12, and I
have a question about the not initialization of list_head,

/*
 * Add a shrinker callback to be called from the vm
 */
struct shrinker *set_shrinker(int seeks, shrinker_t theshrinker)
{
        struct shrinker *shrinker;

        shrinker = kmalloc(sizeof(*shrinker), GFP_KERNEL);
        if (shrinker) {
	        shrinker->shrinker = theshrinker;
	        shrinker->seeks = seeks;
	        shrinker->nr = 0;
	        down_write(&shrinker_rwsem);
	        list_add_tail(&shrinker->list, &shrinker_list);
	        up_write(&shrinker_rwsem);
	}
	return shrinker;
}

As above, the shrinker is allocated from kmalloc, coming from slab
allocator,the list in shrinker is not initialized, directly list_add_tail()
to shrinker_list, don't need to INIT_LIST_HEAD(shrinker->list)?

Thanks,
Best Regards!
Xiaoming.Qing


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Re: Not Initialize the shrinker->list after kmalloc() in mm/vmscan.c(V2.6.12)?

[Rajat Jain]

Hi Qing,

On 4/5/07, qingxiaoming <qing_xiaoming@anyka.com> wrote:
> Dear all:
> I am reading the function set_shrinker() in mm/vmscan.c of V2.6.12, and I
> have a question about the not initialization of list_head,
>
> /*
>  * Add a shrinker callback to be called from the vm
>  */
> struct shrinker *set_shrinker(int seeks, shrinker_t theshrinker)
> {
>        struct shrinker *shrinker;
>
>        shrinker = kmalloc(sizeof(*shrinker), GFP_KERNEL);
>        if (shrinker) {
>                shrinker->shrinker = theshrinker;
>                shrinker->seeks = seeks;
>                shrinker->nr = 0;
>                down_write(&shrinker_rwsem);
>                list_add_tail(&shrinker->list, &shrinker_list);
>                up_write(&shrinker_rwsem);
>        }
>        return shrinker;
> }
>
> As above, the shrinker is allocated from kmalloc, coming from slab
> allocator,the list in shrinker is not initialized, directly list_add_tail()
> to shrinker_list, don't need to INIT_LIST_HEAD(shrinker->list)?
>

IMHO, the linked list is not headed by shrinker->list, rather by
shrinker_list. So the statement

list_add_tail(&shrinker->list, &shrinker_list);

is actually adding shrinker to the list shrinker_list. The shrinker->
list is merely a pointer to help in atttaching the node to the list.

Thanks,

Rajat
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