Re: KVA space problems?

[lost inferno]

You know,  of all the responses i got... it seems yours is the most 
technical and unbiased of the lot. Thank you for that. I wish everyone here 
wasnt so jaded in their own oppinion.  as for the problem... From what you 
wrote, the best idea would be to keep the mbuf limits ether at the defaults 
or lower than the kva space?  and or to run a 5x or later release. The 
reasoning for this is from an experiance i had a few months ago with a dual 
xeon with HT sporaticly locking up under load.  I had hoped to move an old ( 
Free 4.8 ) onto the same hardware without hopfully having to reinstall.


From: Mark Tinguely <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED], [EMAIL PROTECTED]
Subject: Re: KVA space problems?
Date: Wed, 26 May 2004 15:47:41 -0500 (CDT)
This has been seen before and there is at least one open problem report
that the kernel malloc() unexpectantly returns NULL in WAITOK situations.
        http://www.freebsd.org/cgi/query-pr.cgi?pr=i386/53382
                        ---
I think malloc returns before your patch, namely around line 199:
                va = (caddr_t) kmem_malloc(kmem_map, (vm_size_t)ctob(npg), flags
);
                if (va == NULL) {
                        splx(s);
                        return ((void *) NULL);
                }
Although, I agree that the kernel malloc() should not do this, if KVM
is depleted or fragmented to this point, I suspect your changes of simply
retrying again will cause an infinite loop in malloc().
If malloc() sleeps waiting for KVM to be freed, my guess this will lead to
the processes to hang for a long time if not forever.
I think this because people are bumping the MBUFs numbers up and not
changing the KVM size, once the KVM is depleted/fragmented it shouldn't
come down for a long time.
			---
The pre 5.x VM assumes KVM will not be depleted. contigmalloc() used to 
leak
physical pages if the KVM got depleted. I was told "the system will panic
soon anyway, why put them back".

--Mark Tinguely
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