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Only COW on fault if the physical page has retain_count > 1.

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This makes COW pages lazily-but-transparently revert back to read/write.
This commit is contained in:
Andreas Kling 2018-11-05 14:10:18 +01:00
parent 2d045d2a64
commit 9e62eb4856
4 changed files with 17 additions and 2 deletions
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10
Kernel/MemoryManager.cpp
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@ -223,6 +223,16 @@ Region* MemoryManager::region_from_laddr(Process& process, LinearAddress laddr)
bool MemoryManager::copy_on_write(Process& process, Region& region, unsigned page_index_in_region)
{
ASSERT_INTERRUPTS_DISABLED();
if (region.physical_pages[page_index_in_region]->retain_count() == 1) {
#ifdef PAGE_FAULT_DEBUG
dbgprintf(" >> It's a COW page but nobody is sharing it anymore. Remap r/w\n");
#endif
region.cow_map.set(page_index_in_region, false);
remap_region_page(process.m_page_directory, region, page_index_in_region, true);
return true;
}
#ifdef PAGE_FAULT_DEBUG
dbgprintf(" >> It's a COW page and it's time to COW!\n");
#endif