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Kernel: Make purgeable memory a VMObject level concept (again)

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This patch changes the semantics of purgeable memory.

- AnonymousVMObject now has a "purgeable" flag. It can only be set when
  constructing the object. (Previously, all anonymous memory was
  effectively purgeable.)

- AnonymousVMObject now has a "volatile" flag. It covers the entire
  range of physical pages. (Previously, we tracked ranges of volatile
  pages, effectively making it a page-level concept.)

- Non-volatile objects maintain a physical page reservation via the
  committed pages mechanism, to ensure full coverage for page faults.

- When an object is made volatile, it relinquishes any unused committed
  pages immediately. If later made non-volatile again, we then attempt
  to make a new committed pages reservation. If this fails, we return
  ENOMEM to userspace.

mmap() now creates purgeable objects if passed the MAP_PURGEABLE option
together with MAP_ANONYMOUS. anon_create() memory is always purgeable.
This commit is contained in:
Andreas Kling 2021-07-25 01:46:44 +02:00
parent 6bb53d6a80
commit 2d1a651e0a
17 changed files with 189 additions and 1004 deletions
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121
Kernel/VM/AnonymousVMObject.h
View file

@ -10,108 +10,48 @@
#include <Kernel/VM/AllocationStrategy.h>
#include <Kernel/VM/MemoryManager.h>
#include <Kernel/VM/PageFaultResponse.h>
#include <Kernel/VM/PurgeablePageRanges.h>
#include <Kernel/VM/VMObject.h>
namespace Kernel {
class AnonymousVMObject final : public VMObject {
friend class PurgeablePageRanges;
class CommittedCowPages : public RefCounted<CommittedCowPages> {
AK_MAKE_NONCOPYABLE(CommittedCowPages);
public:
CommittedCowPages() = delete;
CommittedCowPages(size_t);
~CommittedCowPages();
NonnullRefPtr<PhysicalPage> allocate_one();
bool return_one();
private:
size_t m_committed_pages;
};
class AnonymousVMObject final : public VMObject {
public:
virtual ~AnonymousVMObject() override;
static RefPtr<AnonymousVMObject> try_create_with_size(size_t, AllocationStrategy);
static RefPtr<AnonymousVMObject> try_create_for_physical_range(PhysicalAddress paddr, size_t size);
static RefPtr<AnonymousVMObject> try_create_with_physical_pages(Span<NonnullRefPtr<PhysicalPage>>);
static RefPtr<AnonymousVMObject> try_create_purgeable_with_size(size_t, AllocationStrategy);
virtual RefPtr<VMObject> try_clone() override;
[[nodiscard]] NonnullRefPtr<PhysicalPage> allocate_committed_page(Badge<Region>, size_t);
[[nodiscard]] NonnullRefPtr<PhysicalPage> allocate_committed_page(Badge<Region>);
PageFaultResponse handle_cow_fault(size_t, VirtualAddress);
size_t cow_pages() const;
bool should_cow(size_t page_index, bool) const;
void set_should_cow(size_t page_index, bool);
void register_purgeable_page_ranges(PurgeablePageRanges&);
void unregister_purgeable_page_ranges(PurgeablePageRanges&);
bool is_purgeable() const { return m_purgeable; }
bool is_volatile() const { return m_volatile; }
int purge();
KResult set_volatile(bool is_volatile, bool& was_purged);
bool is_any_volatile() const;
template<IteratorFunction<VolatilePageRange const&> F>
IterationDecision for_each_volatile_range(F f) const
{
VERIFY(m_lock.is_locked());
// This is a little ugly. Basically, we're trying to find the
// volatile ranges that all share, because those are the only
// pages we can actually purge
for (auto* purgeable_range : m_purgeable_ranges) {
ScopedSpinLock purgeable_lock(purgeable_range->m_volatile_ranges_lock);
for (auto& r1 : purgeable_range->volatile_ranges().ranges()) {
VolatilePageRange range(r1);
for (auto* purgeable_range2 : m_purgeable_ranges) {
if (purgeable_range2 == purgeable_range)
continue;
ScopedSpinLock purgeable2_lock(purgeable_range2->m_volatile_ranges_lock);
if (purgeable_range2->is_empty()) {
// If just one doesn't allow any purging, we can
// immediately bail
return IterationDecision::Continue;
}
for (auto const& r2 : purgeable_range2->volatile_ranges().ranges()) {
range = range.intersected(r2);
if (range.is_empty())
break;
}
if (range.is_empty())
break;
}
if (range.is_empty())
continue;
IterationDecision decision = f(range);
if (decision != IterationDecision::Continue)
return decision;
}
}
return IterationDecision::Continue;
}
template<IteratorFunction<VolatilePageRange const&> F>
IterationDecision for_each_nonvolatile_range(F f) const
{
size_t base = 0;
for_each_volatile_range([&](VolatilePageRange const& volatile_range) {
if (volatile_range.base == base)
return IterationDecision::Continue;
IterationDecision decision = f(VolatilePageRange { base, volatile_range.base - base });
if (decision != IterationDecision::Continue)
return decision;
base = volatile_range.base + volatile_range.count;
return IterationDecision::Continue;
});
if (base < page_count())
return f(VolatilePageRange { base, page_count() - base });
return IterationDecision::Continue;
}
template<VoidFunction<VolatilePageRange const&> F>
IterationDecision for_each_volatile_range(F f) const
{
return for_each_volatile_range([&](auto& range) {
f(range);
return IterationDecision::Continue;
});
}
template<VoidFunction<VolatilePageRange const&> F>
IterationDecision for_each_nonvolatile_range(F f) const
{
return for_each_nonvolatile_range([&](auto range) {
f(move(range));
return IterationDecision::Continue;
});
}
size_t purge();
private:
explicit AnonymousVMObject(size_t, AllocationStrategy);
@ -121,15 +61,6 @@ private:
virtual StringView class_name() const override { return "AnonymousVMObject"sv; }
void update_volatile_cache();
void set_was_purged(VolatilePageRange const&);
size_t remove_lazy_commit_pages(VolatilePageRange const&);
void range_made_volatile(VolatilePageRange const&);
void range_made_nonvolatile(VolatilePageRange const&);
size_t count_needed_commit_pages_for_nonvolatile_range(VolatilePageRange const&);
size_t mark_committed_pages_for_nonvolatile_range(VolatilePageRange const&, size_t);
bool is_nonvolatile(size_t page_index);
AnonymousVMObject& operator=(AnonymousVMObject const&) = delete;
AnonymousVMObject& operator=(AnonymousVMObject&&) = delete;
AnonymousVMObject(AnonymousVMObject&&) = delete;
@ -139,15 +70,15 @@ private:
Bitmap& ensure_cow_map();
void ensure_or_reset_cow_map();
VolatilePageRanges m_volatile_ranges_cache;
bool m_volatile_ranges_cache_dirty { true };
Vector<PurgeablePageRanges*> m_purgeable_ranges;
size_t m_unused_committed_pages { 0 };
Bitmap m_cow_map;
// We share a pool of committed cow-pages with clones
RefPtr<CommittedCowPages> m_shared_committed_cow_pages;
bool m_purgeable { false };
bool m_volatile { false };
bool m_was_purged { false };
};
}