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Discontiguous PageProtect GC support #946

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Merged
merged 2 commits into from
Sep 7, 2023
Merged

Discontiguous PageProtect GC support #946

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24836cb
Fix munprotect
wenyuzhao Sep 6, 2023
1d39728
rewrite
wenyuzhao Sep 7, 2023
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11 changes: 8 additions & 3 deletions src/util/heap/freelistpageresource.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -147,7 +147,7 @@ impl<VM: VMBinding> PageResource<VM> for FreeListPageResource<VM> {
let rtn = self.start + conversions::pages_to_bytes(page_offset as _);
// The meta-data portion of reserved Pages was committed above.
self.commit_pages(reserved_pages, required_pages, tls);
if self.protect_memory_on_release && !new_chunk {
if self.protect_memory_on_release && (!self.common().contiguous || !new_chunk) {
// This check is necessary to prevent us from mprotecting an address that is not yet mapped by mmapper.
// See https://github.com/mmtk/mmtk-core/issues/400.
// It is possible that one thread gets a new chunk, and returns from this function. However, the Space.acquire()
Expand All @@ -158,8 +158,13 @@ impl<VM: VMBinding> PageResource<VM> for FreeListPageResource<VM> {
// If we want to improve and get rid of this loop, we need to move this munprotect to anywhere after the ensure_mapped() call
// in Space.acquire(). We can either move it the option of 'protect_on_release' to space, or have a call to page resource
// after ensure_mapped(). However, I think this is sufficient given that this option is only used for PageProtect for debugging use.
while !MMAPPER.is_mapped_address(rtn) {}
self.munprotect(rtn, self.free_list.size(page_offset as _) as _)
while !new_chunk && !MMAPPER.is_mapped_address(rtn) {}
// Don't unprotect if this is a new unmapped discontiguous chunk
// For a new mapped discontiguous chunk, this should previously be released and protected by us.
// We still need to unprotect it.
if !new_chunk || MMAPPER.is_mapped_address(rtn) {
self.munprotect(rtn, self.free_list.size(page_offset as _) as _)
}
};
Result::Ok(PRAllocResult {
start: rtn,
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