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Fix bug in pagemap when index has many levels

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The pagemap was double incrementing the index level.  This did not
exhibit in any use case of the pagemap as it only used 0 or 1 level of
intermediate index for all current use cases.

This commit fixes the bug, and adds a test that uses the pagemap in a
different configuration that has multiple levels of intermediate index
node.
This commit is contained in:
Matthew Parkinson
2020-09-24 09:40:54 +01:00
committed by Matthew Parkinson
parent e615c33f7a
commit f89f78ad46
2 changed files with 81 additions and 16 deletions
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42
src/mem/pagemap.h
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@@ -184,25 +184,35 @@ namespace snmalloc
size_t shift = TOPLEVEL_SHIFT;
std::atomic<PagemapEntry*>* e = &top[ix];
for (size_t i = 0; i < INDEX_LEVELS; i++)
// This is effectively a
// for (size_t i = 0; i < INDEX_LEVELS; i++)
// loop, but uses constexpr to guarantee optimised version
// where the INDEX_LEVELS in {0,1}.
if constexpr (INDEX_LEVELS != 0)
{
PagemapEntry* value = get_node<create_addr>(e, result);
if (unlikely(!result))
return {nullptr, 0};
shift -= BITS_PER_INDEX_LEVEL;
ix = (static_cast<size_t>(addr) >> shift) & ENTRIES_MASK;
e = &value->entries[ix];
if constexpr (INDEX_LEVELS == 1)
size_t i = 0;
while (true)
{
UNUSED(i);
break;
}
i++;
PagemapEntry* value = get_node<create_addr>(e, result);
if (unlikely(!result))
return {nullptr, 0};
if (i == INDEX_LEVELS)
break;
shift -= BITS_PER_INDEX_LEVEL;
ix = (static_cast<size_t>(addr) >> shift) & ENTRIES_MASK;
e = &value->entries[ix];
if constexpr (INDEX_LEVELS == 1)
{
UNUSED(i);
break;
}
else
{
i++;
if (i == INDEX_LEVELS)
break;
}
}
}
Leaf* leaf = reinterpret_cast<Leaf*>(get_node<create_addr>(e, result));