Re: PATCH - raise max_anon limit

[Tim Hockin <thockin@sun.com>]

On Thu, Feb 12, 2004 at 12:26:14PM -0500, Jim Houston wrote:
> > Maybe Jim can tell us why it's there.  Certainly, the idr interface would
> > be more useful if it just returned id's which start from zero.
> 
> Hi Andrew, Everyone,
> 
> If this new use of idr.c as a sparse bitmap catches on, it might deserve
> a new flavor which would not waste the space for the pointer array
> at the lowest layer.

the only place I found using idr as-is is posix timers.  I haven't looked at
it's usage pattern much, but I assume it does use the pointers.  I guess
we're using up sizeof(void *) for every id we allocate, which is yuck.

Do we need to clone idr.c into bitmap.c and simplify?

> George Anzinger rewrote most of my code.  The r in idr.c is for
> immediate reuse.  His version picks the lowest available bit in the

That is the behavior that makes most sense, to me.

> The rational for avoiding immediate reuse of id values is to catch
> application errors.   Consider:
> 
> 	fd1 = open_like_call(...);
> 	read(fd1,...);
> 	close(fd1);
> 	fd2 = open_like_call(...);
> 	write(fd1...);
> 
> If fd2 has a different value than the recently closed fd1, the
> error is detected immediately.

Is that really worth working around in such a gross way?  No offense to the
idea, but that's a pretty dumb bug to be hacking a failsafe for :)

-- 
Tim Hockin
Sun Microsystems, Linux Software Engineering
thockin@sun.com
All opinions are my own, not Sun's