Re: [PATCH] VM fix for 2.4.0-test9 & OOM handler

[jg@pa.dec.com (Jim Gettys)]

"Albert D. Cahalan" <acahalan@cs.uml.edu> writes: 
> Date: Mon, 9 Oct 2000 19:13:25 -0400 (EDT)
>
> >> From: Linus Torvalds <torvalds@transmeta.com>
> 
> >> One of the biggest bitmaps is the background bitmap. So you have a
> >> client that uploads it to X and then goes away. There's nobody to
> >> un-count to by the time X decides to switch to another background.
> >
> > Actually, the big offenders are things other than the background
> > bitmap: things like E do absolutely insane things, you would not
> > believe (or maybe you would).  The background pixmap is generally
> > in the worst case typically no worse than 4 megabytes (for those
> > people who are crazy enough to put images up as their root window
> > on 32 bit deep displays, at 1kX1k resolution).
> 
> Still, it would be nice to recover that 4 MB when the system
> doesn't have any memory left.
> 

Yup. The X server could give back the memory for some cases like the
background without too much hackery.

> X, and any other big friendly processes, could participate in
> memory balancing operations. X could be made to clean out a
> font cache when the kernel signals that memory is low. When
> the situation becomes serious, X could just mmap /dev/zero over
> top of the background image.

I agree in principle, though the problem is difficult, as the memory pool 
may get fragmented... Most memory usage is less monolithic than the 
background pixmap.

And maintaining separate memory pools often wastes more memory than it
saves.

> 
> Netscape could even be hacked to dump old junk... or if it is
> just too leaky, it could exec itself to fix the problem.

Netscape 4.x is hopeless; it is leakier than the Titanic.  There is hope 
for Mozilla.
				- Jim


--
Jim Gettys
Technology and Corporate Development
Compaq Computer Corporation
jg@pa.dec.com

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