msm8909go:/ $ df -h Filesystem Size Used Avail Use% Mounted on rootfs 430M 1.6M 428M 1% / tmpfs 442M 0 442M 0% /mnt /dev/block/mmcblk0p34 5.5G 5.2G 0 100% /data // -> data分区填满 /dev/block/mmcblk0p31 104M 1.0M 100M 2% /cache msm8909go:/ $ ps -A | grep system_s system 1709 1517 1018068 46772 0 R system_server msm8909go:/ $ uptime 13:22:16 up 1:06, 0 users, load average: 4.61, 4.63, 3.79 msm8909go:/ $ dmesg dmesg: klogctl: Permission denied msm8909go:/ $ ps -A | grep zygote root 1882 1 967528 56388 poll_schedule_timeout 0 S zygote msm8909go:/ $ msm8909go:/ $ ps -A | grep system_s system 2073 1882 1011152 38588 0 R system_server msm8909go:/ $
system_server一直在重启。
再来看下logcat，发现如下zygote log:
01-06 03:25:49.287 1986 1986 E patchoat: Failed to create symlink at /data/dalvik-cache/arm/system@framework@boot.oat error(28): No space left on device 01-06 03:25:49.288 1986 1986 W patchoat: Current thread not detached in Runtime shutdown 01-06 03:25:48.959 1898 1898 W zygote : Pruning dalvik cache because of low-memory situation. 01-06 03:25:48.960 1898 1898 W zygote : Failed to create boot marker.: No such file or directory 01-06 03:25:48.960 1898 1898 W zygote : Low-memory situation: only 0.17 megabytes available, need at least 50. Preemptively pruning the dalvik cache. 01-06 03:25:48.961 1898 1898 I zygote : Pruning dalvik-cache since we are relocating an image and will need to recompile 01-06 03:25:48.962 1898 1898 I zygote : RelocateImage: /system/bin/patchoat --input-image-location=/system/framework/boot.art --output-image-file=/data/dalvik-cache/arm/system@framework@boot.art --instruction-set=arm --base-offset-delta=-6152192 01-06 03:25:49.303 1898 1898 E zygote : Could not create image space with image file '/system/framework/boot.art'. Attempting to fall back to imageless running. Error was: Cannot relocate image /system/framework/boot.art to /data/dalvik-cache/arm/system@framework@boot.art: Failed execv(/system/bin/patchoat --input-image-location=/system/framework/boot.art --output-image-file=/data/dalvik-cache/arm/system@framework@boot.art --instruction-set=arm --base-offset-delta=-6152192) because non-0 exit status 01-06 03:25:49.303 1898 1898 E zygote : Attempted image: /system/framework/boot.art
能看出来有No space left, Low-memory situation，这些都是ART虚拟机的东东，让我们先简单了解下ART相关概念和背景:
Google官方解释：
Android runtime (ART) is the managed runtime used by applications and some system services on Android. ART and its predecessor Dalvik were originally created specifically for the Android project. ART as the runtime executes the Dalvik Executable format and Dex bytecode specification.
ART and Dalvik are compatible runtimes running Dex bytecode, so apps developed for Dalvik should work when running with ART. However, some techniques that work on Dalvik do not work on ART.
ART introduces ahead-of-time (AOT) compilation, which can improve app performance. ART also has tighter install-time verification than Dalvik.
At install time, ART compiles apps using the on-device dex2oat tool. This utility accepts DEX files as input and generates a compiled app executable for the target device. The utility should be able to compile all valid DEX files without difficulty. However, some post-processing tools produce invalid files that may be tolerated by Dalvik but cannot be compiled by ART.
std::unique_ptr<ImageSpace> ImageSpace::CreateBootImage(constchar* image_location, const InstructionSet image_isa, bool secondary_image, std::string* error_msg){ ... // Step 0.b: If we're the zygote, check for free space, and prune the cache preemptively, // if necessary. While the runtime may be fine (it is pretty tolerant to // out-of-disk-space situations), other parts of the platform are not. // // The advantage of doing this proactively is that the later steps are simplified, // i.e., we do not need to code retries. ... if (is_zygote && dalvik_cache_exists) { DCHECK(!dalvik_cache.empty()); std::string local_error_msg; if (!CheckSpace(dalvik_cache, &local_error_msg)) { LOG(WARNING) << local_error_msg << " Preemptively pruning the dalvik cache."; PruneDalvikCache(image_isa);
// Read the free space of the cache partition and make a decision whether to keep the generated // image. This is to try to mitigate situations where the system might run out of space later. staticboolCheckSpace(const std::string& cache_filename, std::string* error_msg){ // Using statvfs vs statvfs64 because of b/18207376, and it is enough for all practical purposes. structstatvfs buf;
int res = TEMP_FAILURE_RETRY(statvfs(cache_filename.c_str(), &buf)); if (res != 0) { // Could not stat. Conservatively tell the system to delete the image. *error_msg = "Could not stat the filesystem, assuming low-memory situation."; returnfalse; }
uint64_t fs_overall_size = buf.f_bsize * static_cast<uint64_t>(buf.f_blocks); // Zygote is privileged, but other things are not. Use bavail. uint64_t fs_free_size = buf.f_bsize * static_cast<uint64_t>(buf.f_bavail);
// Take the overall size as an indicator for a tmpfs, which is being used for the decryption // environment. We do not want to fail quickening the boot image there, as it is beneficial // for time-to-UI. if (fs_overall_size > kTmpFsSentinelValue) { if (fs_free_size < kLowSpaceValue) { *error_msg = StringPrintf("Low-memory situation: only %4.2f megabytes available, need at " "least %" PRIu64 ".", static_cast<double>(fs_free_size) / MB, kLowSpaceValue / MB); returnfalse; } } returntrue; }
先看注释：
// Read the free space of the cache partition and make a decision whether to keep the generated // image. This is to try to mitigate situations where the system might run out of space later.
// We are relocating or generating the core image. We should get rid of everything. It is all // out-of-date. We also don't really care if this fails since it is just a convenience. // Adapted from prune_dex_cache(const char* subdir) in frameworks/native/cmds/installd/commands.c // Note this should only be used during first boot. staticvoidPruneDalvikCache(InstructionSet isa){ CHECK_NE(isa, kNone); // Prune the base /data/dalvik-cache. // Note: GetDalvikCache may return the empty string if the directory doesn't // exist. It is safe to pass "" to DeleteDirectoryContents, so this is okay. impl::DeleteDirectoryContents(GetDalvikCache("."), false); // Prune /data/dalvik-cache/<isa>. impl::DeleteDirectoryContents(GetDalvikCache(GetInstructionSetString(isa)), false);
// Be defensive. There should be a runtime created here, but this may be called in a test. if (Runtime::Current() != nullptr) { Runtime::Current()->SetPrunedDalvikCache(true); } }
就是/data/dalvik-cache/这个目录删了，正常启动的手机看下：
8909go:/data/dalvik-cache # du -h 269M ./arm 269M .
占用了不少啊。
我们再继续看create boot image:
// Step 1: Check if we have an existing and relocated image.
// Step 1.a: Have files in system and cache. Then they need to match. if (found_image && has_system && has_cache) { std::string local_error_msg; // Check that the files are matching. if (ChecksumsMatch(system_filename.c_str(), cache_filename.c_str(), &local_error_msg)) { std::unique_ptr<ImageSpace> relocated_space = ImageSpaceLoader::Load(image_location, cache_filename, is_zygote, is_global_cache, /* validate_oat_file */false, &local_error_msg); if (relocated_space != nullptr) { return relocated_space; } } error_msgs.push_back(local_error_msg); }
// Step 1.b: Only have a cache file. if (found_image && !has_system && has_cache) { std::string local_error_msg; std::unique_ptr<ImageSpace> cache_space = ImageSpaceLoader::Load(image_location, cache_filename, is_zygote, is_global_cache, /* validate_oat_file */true, &local_error_msg); if (cache_space != nullptr) { return cache_space; } error_msgs.push_back(local_error_msg); }
if (have_android_data && *dalvik_cache_exists) { // Always set output location even if it does not exist, // so that the caller knows where to create the image. // // image_location = /system/framework/boot.art // *image_filename = /data/dalvik-cache/<image_isa>/boot.art std::string error_msg; if (!GetDalvikCacheFilename(image_location, dalvik_cache->c_str(), cache_filename, &error_msg)) { LOG(WARNING) << error_msg; return *has_system; } *has_cache = OS::FileExists(cache_filename->c_str()); } return *has_system || *has_cache;
ok, file in system指的是/system/framework/boot.art，file in cache指的是/data/dalvik-cache//boot.art。
// Step 3: We do not have an existing image in /system, so generate an image into the dalvik // cache. This step fails if this is a secondary image. if (!has_system) { std::string local_error_msg; if (!Runtime::Current()->IsImageDex2OatEnabled()) { local_error_msg = "Image compilation disabled."; } elseif (secondary_image) { local_error_msg = "Cannot compile a secondary image."; } elseif (ImageCreationAllowed(is_global_cache, image_isa, &local_error_msg)) { bool compilation_success = GenerateImage(cache_filename, image_isa, &local_error_msg); if (compilation_success) { std::unique_ptr<ImageSpace> compiled_space = ImageSpaceLoader::Load(image_location, cache_filename, is_zygote, is_global_cache, /* validate_oat_file */false, &local_error_msg); if (compiled_space != nullptr) { return compiled_space; } } } error_msgs.push_back(StringPrintf("Cannot compile image to %s: %s", cache_filename.c_str(), local_error_msg.c_str())); }
Pre-ART, Android used the Zygote to fork each app process and preload and preinitialize some classes for optimization purposes. On ART, the set of jar libraries that should be preloaded into each app process is compiled once into the so called boot image. It consists of two files, boot.oat and boot.art. Boot.oat contains the compiled code while boot.art contains a preinitialized heap etc. Both are also generated by dex2oat. This boot image is loaded into each app’s process as an optimization.
