Purge linker block allocators before leaving linker
This is the second attempt to purge linker block allocators. Unlike the
previously reverted change which purge allocators whenever all objects
are freed, we only purge right before control leaves the linker. This
limits the performance impact to one munmap() call per dlopen(), in
most cases.
Bug: 112073665
Test: Boot and check memory usage with 'showmap'.
Test: Run camear cold start performance test.
Change-Id: I02c7c44935f768e065fbe7ff0389a84bd44713f0
diff --git a/linker/linker.cpp b/linker/linker.cpp
index d0c740b..428dd25 100644
--- a/linker/linker.cpp
+++ b/linker/linker.cpp
@@ -536,6 +536,10 @@
allocator_.free(ptr);
}
+ static void purge() {
+ allocator_.purge();
+ }
+
private:
static LinkerBlockAllocator allocator_;
};
@@ -553,6 +557,10 @@
static void free(T* ptr) {
SizeBasedAllocator<sizeof(T)>::free(ptr);
}
+
+ static void purge() {
+ SizeBasedAllocator<sizeof(T)>::purge();
+ }
};
class LoadTask {
@@ -2074,6 +2082,8 @@
ns == nullptr ? "(null)" : ns->get_name(),
ns);
+ auto purge_guard = android::base::make_scope_guard([&]() { purge_unused_memory(); });
+
auto failure_guard = android::base::make_scope_guard(
[&]() { LD_LOG(kLogDlopen, "... dlopen failed: %s", linker_get_error_buffer()); });
@@ -4069,3 +4079,17 @@
}
return it->second;
}
+
+void purge_unused_memory() {
+ // For now, we only purge the memory used by LoadTask because we know those
+ // are temporary objects.
+ //
+ // Purging other LinkerBlockAllocator hardly yields much because they hold
+ // information about namespaces and opened libraries, which are not freed
+ // when the control leaves the linker.
+ //
+ // Purging BionicAllocator may give us a few dirty pages back, but those pages
+ // would be already zeroed out, so they compress easily in ZRAM. Therefore,
+ // it is not worth munmap()'ing those pages.
+ TypeBasedAllocator<LoadTask>::purge();
+}
diff --git a/linker/linker.h b/linker/linker.h
index 91d3ddf..964c266 100644
--- a/linker/linker.h
+++ b/linker/linker.h
@@ -186,3 +186,5 @@
void increment_dso_handle_reference_counter(void* dso_handle);
void decrement_dso_handle_reference_counter(void* dso_handle);
+
+void purge_unused_memory();
diff --git a/linker/linker_block_allocator.cpp b/linker/linker_block_allocator.cpp
index d72cad3..fdb4c85 100644
--- a/linker/linker_block_allocator.cpp
+++ b/linker/linker_block_allocator.cpp
@@ -55,7 +55,8 @@
: block_size_(
round_up(block_size < sizeof(FreeBlockInfo) ? sizeof(FreeBlockInfo) : block_size, 16)),
page_list_(nullptr),
- free_block_list_(nullptr)
+ free_block_list_(nullptr),
+ allocated_(0)
{}
void* LinkerBlockAllocator::alloc() {
@@ -76,6 +77,8 @@
memset(block_info, 0, block_size_);
+ ++allocated_;
+
return block_info;
}
@@ -104,6 +107,8 @@
block_info->num_free_blocks = 1;
free_block_list_ = block_info;
+
+ --allocated_;
}
void LinkerBlockAllocator::protect_all(int prot) {
@@ -154,3 +159,18 @@
abort();
}
+
+void LinkerBlockAllocator::purge() {
+ if (allocated_) {
+ return;
+ }
+
+ LinkerBlockAllocatorPage* page = page_list_;
+ while (page) {
+ LinkerBlockAllocatorPage* next = page->next;
+ munmap(page, kAllocateSize);
+ page = next;
+ }
+ page_list_ = nullptr;
+ free_block_list_ = nullptr;
+}
diff --git a/linker/linker_block_allocator.h b/linker/linker_block_allocator.h
index 0c54b93..8ae4094 100644
--- a/linker/linker_block_allocator.h
+++ b/linker/linker_block_allocator.h
@@ -50,6 +50,9 @@
void free(void* block);
void protect_all(int prot);
+ // Purge all pages if all previously allocated blocks have been freed.
+ void purge();
+
private:
void create_new_page();
LinkerBlockAllocatorPage* find_page(void* block);
@@ -57,6 +60,7 @@
size_t block_size_;
LinkerBlockAllocatorPage* page_list_;
void* free_block_list_;
+ size_t allocated_;
DISALLOW_COPY_AND_ASSIGN(LinkerBlockAllocator);
};
diff --git a/linker/linker_main.cpp b/linker/linker_main.cpp
index b0c27dc..7486cd7 100644
--- a/linker/linker_main.cpp
+++ b/linker/linker_main.cpp
@@ -503,6 +503,10 @@
fflush(stdout);
#endif
+ // We are about to hand control over to the executable loaded. We don't want
+ // to leave dirty pages behind unnecessarily.
+ purge_unused_memory();
+
ElfW(Addr) entry = exe_info.entry_point;
TRACE("[ Ready to execute \"%s\" @ %p ]", si->get_realpath(), reinterpret_cast<void*>(entry));
return entry;