Re: [lc-devel] Chunk list issues

[Nitin G. <nit...@gm...>]

Hi Mauricio,

Mauricio Lin wrote:
> On 6/21/06, Nitin Gupta <nit...@gm...> wrote:
>> Mauricio Lin wrote:
>> > Regarding the master chunk list (chunks) in the struct chunk, does it
>> > store the chunks of one page cache or several page caches? Will be
>> > there one master chunk list per page cache radix tree?
>>
>> 'master chunk list' is list of all chunks -- these chunks may be part 
>> of a file,
>> part of anon page, or free chunks. Its there to easily merge 
>> physically adjacent
>> chunks when a chunk is freed.
> 
> You mean there will be one master chunk list for several page cache
> radix tree, right?
> 

Yes.
In other words: nodes of several page cache radix trees will be replaces by 
chunk_head's. These chunk_head's point to corres. list of chunks. And all these 
chunks are linked together by master chunk list (MCL).

>>
>> >
>> > I also wonder where the chunk list header will be stored. For instance
>> > the list header of task_struct is stored in the tasks field of
>> > init_task, so when an insertion happens in the list of task_struct,
>> > something like that is used:
>> >
>> > list_add_tail(&p->tasks, &init_task.tasks);
>> >
>> > where the first argument is the element to be inserted and the second
>> > argument corresponds the list header of task_struct.
>> > Thus where the list header of chunks will be stored? Any idea?
>> >
>>
>> A compressed page is stored in many chunks. chunk_head->chunk_list is 
>> made to
>> point to first of these chunks and these 'related' chunks are linked 
>> together
>> using chunk->next
> 
> OK, I know about the chunk_list purpose, but chunk_list is not the
> header of master chunk list, since it is not a list_head. What I am
> trying to say is if you want to add something in the master chunk
> list, you have to use a function as list_add_tail() (or similar one in
> include/linux/list.h) and a header list is needed for representing and
> manipulating the master chunk list. If you are going to add something
> in the master chunk list, certainly functions in include/linux/list.h
> need be used. Let's suppose that list_add_tail() function is used to
> insert a chunk in the list, so in this way something like this is
> used:
> 
> list_add_tail(&chk->chunks, chunk_list_head);
> 
> chk is a instance of struct chunk, where the field "chunks" is used to
> link to the list.
> chunk_list_head is the header of chunk list of type 'list_head'
> (because every list has a header)
> 
> Such can be declared and initiliazed as:
> static LIST_HEAD(chunk_list_head);
> 
> The chunk_list_head  (header of master chunk list) must be stored in
> some place. So my question is where it is going to be stored ?
> 

I was still stuck with 'related chunk list' (ok, RCL) while answering you :)
All these lists: MCL, LRU_{page_cache_clean,page_cache_dirty,anon}, 
Free_{good,bad,ugly} will have their heads as globals in mm/ccache.c

Of these:
MCL lists use chunk->chunks (doubly linked)
LRU lists use chunk_head->lru (doubly linked)
Free lists use chunk->next (singly linked)


Cheers,
Nitin Gupta