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Handle vm_phys returning NULL in vm_page_alloc()
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Authored by adrian on Apr 30 2015, 5:12 AM.


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When using VM domains, it's possible that unbalanced VM domain memory pressure
(or even different sized memory domains) may lead to the global VM thresholds saying
there's memory, but vm_phys returning NULL. In this instance, a NULL page
is dereferenced, and things blow up.

This change has it return NULL, which prevents the system from crashing.

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rS FreeBSD src repository - subversion
Lint OK
No Unit Test Coverage

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adrian retitled this revision from to Handle vm_phys returning NULL in vm_page_alloc().
adrian updated this object.
adrian edited the test plan for this revision. (Show Details)
adrian added reviewers: alc, kmacy, kib.

Is this something that happens in the stock sources, or the situation to occur requires patches to limit allocation of a new page to the specific domain ? I think that if applied to the HEAD, it would defeat the KASSERT(m != NULL) right after the cited block, and break invariants.

I haven't triggered it in stock sources - this happens in my VM policy branch. There are some use cases where the memory must come from a particular domain, so VM phys memory allocation can get unbalanced.

I think that this change should be abandoned.