madvise away app image dex cache arrays
This saves ram and PSS by reducing the number of mapped pages. Also
PROT_NONE the dex cache arrays section to make accesses fault.
virtual shared shared private private
size RSS PSS clean dirty clean dirty swap
-------- -------- -------- -------- -------- -------- -------- --------
Before:
/data/app/com.facebook.katana-2/oat/arm/base.art
52484 52144 43522 17244 0 0 34900 0
/data/app/com.google.android.apps.maps-2/oat/arm/base.art
6876 6816 6816 0 0 2008 4808 0
After:
/data/app/com.facebook.katana-2/oat/arm/base.art
52484 49204 42032 14344 0 0 34860 0
/data/app/com.google.android.apps.maps-2/oat/arm/base.art
6876 6388 6388 0 0 1584 4804 0
Bug: 22858531
Change-Id: I87888a7c1518a92736dbd29eed338e7472ae3587
diff --git a/runtime/class_linker.cc b/runtime/class_linker.cc
index e4f492b..205ba3e 100644
--- a/runtime/class_linker.cc
+++ b/runtime/class_linker.cc
@@ -1669,6 +1669,22 @@
forward_dex_cache_arrays);
class_table->Visit(visitor);
}
+ // forward_dex_cache_arrays is true iff we copied all of the dex cache arrays into the .bss.
+ // In this case, madvise away the dex cache arrays section of the image to reduce RAM usage and
+ // mark as PROT_NONE to catch any invalid accesses.
+ if (forward_dex_cache_arrays) {
+ const ImageSection& dex_cache_section = header.GetImageSection(
+ ImageHeader::kSectionDexCacheArrays);
+ uint8_t* section_begin = AlignUp(space->Begin() + dex_cache_section.Offset(), kPageSize);
+ uint8_t* section_end = AlignDown(space->Begin() + dex_cache_section.End(), kPageSize);
+ if (section_begin < section_end) {
+ madvise(section_begin, section_end - section_begin, MADV_DONTNEED);
+ mprotect(section_begin, section_end - section_begin, PROT_NONE);
+ VLOG(image) << "Released and protected dex cache array image section from "
+ << reinterpret_cast<const void*>(section_begin) << "-"
+ << reinterpret_cast<const void*>(section_end);
+ }
+ }
}
VLOG(class_linker) << "Adding image space took " << PrettyDuration(NanoTime() - start_time);
return true;
