On Mon, Mar 15, 2004 at 10:37:21 +0300, Ruslan U. Zakirov wrote:
> Zeeshan Ali wrote:
> >Hello,
> >
> >
> >>The linked list implementation is generic, and it is
> >>not kernel-oriented as you claimed.
> >
It is generic (can be used for any list) and not kernel-oriented (you
can include linux/list.h to user-space application and use it).
> >
> > It certainly is, as it requires the list_head to
> >be the part of the data. Please correct me if i am
> >wrong.
Yes, it requires so. But of course, you are free to build external list
on top of it:
struct ext_list {
list_head list;
void * data;
};
> You are wrong because I think that it's benefit of kernel indirect(with
> magic) lists, it saves memory. I don't know place where it's better to
> use direct pointer in list element. Do you know?
>
> Why it's benefit? Because if you want list of 'XObj' then often(allways)
> have more(or equal) list elements then 'XObj' instances altogether.So
> memory usage for current kernel lists:
> sizeof(pointer)*(2*"NumberOfListElements"+"NumberOfXObj")
>
> in case of GList:
> sizeof(pointer)*(3*"NumberOfListElements")
>
> I think that at least one time you have to put any 'XObj' instance in
> some list so we got equality of memory usage, but if we want more
> ocurances of instance then GList loose on memory.
Internal linked lists (with next/prev as part of data) only allows the
structure to be part of one list. Of course, you can have more than one
list_head included, but they can't be used interchangeably. In kernel,
it turns out that most object are on exactly one list of a kind. Eg.
dentry is in a hash (global) and in children list of exactly one parent.
For this, internal lists use less memory and are a little bit faster
(one indirection less).
On the other hand, when you need to put arbitrary stuff on temporary
lists, usualy on more than one at a time, as is often done in glib,
external lists are the only way.
OT:
> Yes, hashes are good. Simplify programming a lot.
> I know only Perl language which support hashes in core, but it's on
> arrays so perfomance isn't as good as wanted.
Python does too. As does tcl. Most scripting languages do. C++ does too
(there are hashes in STL (standard template library)).
Yes, perl's performance on hashes is poor -- it's the only think where
it's slower than python.
-------------------------------------------------------------------------------
Jan 'Bulb' Hudec <bulb@ucw.cz>
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