vm_phys: do not ignore phys_avail[] segments that do not fit completely into vm_phys segments

[kib]

Summary

If phys_avail[] segment only intersect with some vm_phys segment, add pages from it to the free list that belong to the given vm_phys_seg, instead of dropping them.

The vm_phys segments are generally result of subdivision of phys_avail segments, for instance DMA32 or LOWMEM boundaries split them. On amd64, after UEFI in-place kernel activation (copy_staging disable) was enabled, we typically have a large phys_avail[] segment below 4G which crosses LOWMEM (1M) boundary. With the current way of requiring phys_avail[] fully fit into vm_phys_seg, this memory was ignored.

[madpilot]

I confirm that with this patch applied my system is now able to see all its RAM.

Thank you!

[markj]

sys/vm/vm_page.c

776

This comment no longer holds.

[kib]

Update comment.

[alc]

sys/vm/vm_page.c

774–776

[kib]

Reword comment, by Alan.

[markj]

sys/vm/vm_page.c

798–799

Isn't it possible for some of the excluded range of the phys_seg to be present in a different phys_avail[] region?

[kib]

sys/vm/vm_page.c

798–799

Do you mean that this break statement should be removed?

798–799

And the condition seg->start< phys_avail[i] replaced by seg->end < phys_avail[i] perhaps

[kib]

Walk over all phys_avail[] segments which overlap with our vm_phys_seg when gathering the vm_phys_seg' pages

[alc]

sys/vm/vm_page.c

778–779

Why not test for equality here? It seems pointless to allow execution to continue if they are equal.

783

Shouldn't this be startp - seg->start?