From owner-freebsd-bugs  Mon Oct 12 11:08:03 1998
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To: Kevin Day <toasty@home.dragondata.com>
cc: freebsd-bugs@FreeBSD.ORG
Subject: Re: bin/8275: w/top/etc randomly fail with 'Cannot allocate memory' 
In-reply-to: Your message of "Mon, 12 Oct 1998 09:00:01 PDT."
             <199810121600.JAA21354@freefall.freebsd.org> 
From: David Greenman <dg@root.com>
Reply-To: dg@root.com
Date: Mon, 12 Oct 1998 11:06:12 -0700
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> > "home.dragondata.com" <root@shell1.dragondata.com> writes:
> > > bash-2.02# w
> > >  1:10PM  up 19 days, 54 mins, 7 users, load averages: 0.08, 0.48, 0.73
> > > USER     TTY FROM              LOGIN@  IDLE WHAT
> > > w: kvm_getprocs: Cannot allocate memory: Cannot allocate memory

   The problem is caused by the process table growing while w/top is trying
to read the data. Via kvm_getprocs, which is a libkvm library function, they
first make a syscall to determine how much memory is needed, and then after
allocating the appropriate amount of memory, do another syscall to get the
data. In-between the calls, the process table changed and made the needed
amount of memory assumption invalid. 
   kvm_getprocs gives up too easily. It should retry the above procedure a
few times before giving up. It should also add in some padding in order to
make it a bit more resilient to minor increases in the number of processes
in the system.

-DG

David Greenman
Co-founder/Principal Architect, The FreeBSD Project

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