Re: Bug in 2.4.26 in mm/filemap.c when using RLIMIT_RSS

[Marcelo Tosatti <marcelo.tosatti@cyclades.com>]

On Thu, Jan 27, 2005 at 07:38:49AM +0100, Ake wrote:

> On Wed, Jan 26, 2005 at 12:49:04PM -0200, Marcelo Tosatti wrote:
> > > There is also a misinformative comment in fs/proc/array.c
 > > in proc_pid_stat where it says
> > > mm ? mm->rss : 0, /* you might want to shift this left 3 */
> > > the number 3 should probably be PAGE_SHIFT-10.
> 
> Don't forget the comment (it's still there in 2.6) :-)
> 
> > Amazing that this has never been noticed before - I bet not many people use RSS 
> > limits with madvise().
> 
> Neither do we. :-)
> 
> I just found it when trying to figure out if the kernel actually used
> any of the rlimits and if so how.
> (Trying to make PBS work correctly)
> 
> > This transform the rlimit in pages before the comparison, can you please test
> > it.
> > 
> > --- a/mm/filemap.c.orig	2004-11-17 09:54:22.000000000 -0200
> > +++ b/mm/filemap.c	2005-01-26 15:21:10.614842296 -0200
> > @@ -2609,6 +2609,9 @@
> >  	error = -EIO;
> >  	rlim_rss = current->rlim ?  current->rlim[RLIMIT_RSS].rlim_cur :
> >  				LONG_MAX; /* default: see resource.h */
> > +
> > +	rlim_rss = (rlim_rss & PAGE_MASK) >> PAGE_SHIFT;
> > +
> >  	if ((vma->vm_mm->rss + (end - start)) > rlim_rss)
> >  		return error;
> 
> Since we don't use it i can't really test it, but a visual inspection is
> good enough in this simple case. And since this is the only place in 2.4
> that RLIMIT_RSS is used, the problem is solved.
> 
> BTW do you know if there is any plans for 2.6++ to actually use
> RLIMIT_RSS? I saw a hint in that direction in mm/thrash.c
> grab_swap_token but it is commented out and only skeleton code...

Nope, RLIMIT_RSS does not seem to be used at all in v2.6:

linux-2.6.11-rc1 # findgrep RLIMIT_RSS
./fs/proc/array.c
./include/asm-arm26/resource.h
./include/asm-ia64/resource.h
./include/asm-frv/resource.h
./include/asm-i386/resource.h
./include/asm-alpha/resource.h
./include/asm-ppc64/resource.h
./include/asm-x86_64/resource.h
./include/asm-s390/resource.h
./include/asm-mips/resource.h
./include/asm-sparc64/resource.h
./include/asm-cris/resource.h
./include/asm-v850/resource.h
./include/asm-m68k/resource.h
./include/asm-sparc/resource.h
./include/asm-parisc/resource.h
./include/asm-arm/resource.h
./include/asm-sh/resource.h
./include/asm-m32r/resource.h
./include/asm-h8300/resource.h
./include/asm-ppc/resource.h

> I'm asking since the above code piece has been removed.

Its there for compatibility reasons, support for it might be added
in the future?