Subject: Re: "filtered" shared libraries
To: None <,>
From: der Mouse <mouse@Rodents.Montreal.QC.CA>
List: current-users
Date: 11/01/2001 20:54:01
>>> Sounds like a cool idea, does already do this?
>> Isn't this called "demand paging"?
> Thanks for reminding me!  I wonder why anyone would need "lazy
> loading" to be explicitly supported by the link loader.

Primarily, I would think, because it guarantees functional grouping.
If you filter-load stdio, strings, and the resolver, let's say, and use
only stdio, you page in only stdio.  If you load a single shared
library containing all of them, you page in all of stdio and numerous
bits and pieces of other stuff - everything that happens to reside in
the same page as a piece of stdio.  Depending on how the library is
built, this may be little or it may be a lot.  Has anyone checked to
see how good the functional clumping is in libc?

> I guess with "lazy loading" you could have even less mmap'ed in the
> first place, but why would you need that on a server system?

VM consumption?  The ability to replace one library without having to
rebuild and replace a whole humngous blob?  The ability to defer
deciding exactly which library to actually use until as late as
possible?  (For example, I could imagine a libc that lazily loads
shared libraries for string stuff depending on wihch locale is in use.)

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