I have a question about scavenging arising one of the runtime tests in
runtime/mpagealloc.go. The test in question is the " AllFree1" test case in
TestPageAllocAlloc.
According to my understanding, in the runtime, there is a distinction
between reclaiming memory and scavenging memory. Reclaiming memory is
reusing free memory for allocations while scavenging is returning memory
back to the OS that is no longer needed by the application.
Step 1. the test starts off by setting up some scavenging state by
scavening one page at index 0, and two pages starting at index two
scav: map[ChunkIdx][]BitRange{
BaseChunkIdx: {{0, 1}, {2, 2}},
},
If you inspect the bitmap, you can see the scavenged pages set starting at
the appropriate index
0000000000000000000000000000000000000000000000000000000000001101
Step 2. It then allocates 5 pages in succession
for iter, i := range v.5hits {
address, scav := b.Alloc(i.npages)
}
Step 3. Afterwards, if you print the bits you can see the five allocations
in the first positions
The 5 allocations
0000000000000000000000000000000000000000000000000000000000011111
The corresponding scavenged bit map is all set to 0, so the allocations
used the scavenged pages:
0000000000000000000000000000000000000000000000000000000000000000
So my question is....is that "scavenging" or more properly "reclaiming"?
The allocations occupy the positions that were previously scavenged, so I'm
guessing the memory has been re-used (in the logic of the test) rather than
returned to the OS.
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