properly support a file-backed nvm cache

Summary:
Previously, in order to use a file as the backing store of nvm cache, user needs to create the file
with the given size a priori, hurting the usability of the feature. This change fixes it so that the
new file with the given size is automatically created if not exist. Also, if the file exists with
different size, this change will allow the cachebench to ftruncate or fallocate to the given size
automatically.

Reviewed By: therealgymmy

Differential Revision: D44154281

fbshipit-source-id: c622102d4d67b64da83dcad4fdade66473d70a1f

Author: Jaesoo Lee

cachelib/cachebench/cache/Cache-inl.h

@@ -124,24 +124,41 @@ Cache<Allocator>::Cache(const CacheConfig& config,
       // already have a file, user provided it. We will also keep it around
       // after the tests.
       auto path = config_.nvmCachePaths[0];
-      if (cachelib::util::isDir(path)) {
+      bool isDir;
+      try {
+        isDir = cachelib::util::isDir(path);
+      } catch (const std::system_error& e) {
+        XLOGF(INFO, "nvmCachePath {} does not exist", path);
+        isDir = false;
+      }
+
+      if (isDir) {
         const auto uniqueSuffix = folly::sformat("nvmcache_{}_{}", ::getpid(),
                                                  folly::Random::rand32());
         path = path + "/" + uniqueSuffix;
         util::makeDir(path);
         nvmCacheFilePath_ = path;
+        XLOGF(INFO, "Configuring NVM cache: directory {} size {} MB", path,
+              config_.nvmCacheSizeMB);
         nvmConfig.navyConfig.setSimpleFile(path + "/navy_cache",
                                            config_.nvmCacheSizeMB * MB,
                                            true /*truncateFile*/);
       } else {
-        nvmConfig.navyConfig.setSimpleFile(path, config_.nvmCacheSizeMB * MB);
+        XLOGF(INFO, "Configuring NVM cache: simple file {} size {} MB", path,
+              config_.nvmCacheSizeMB);
+        nvmConfig.navyConfig.setSimpleFile(path, config_.nvmCacheSizeMB * MB,
+                                           true /* truncateFile */);
       }
     } else if (config_.nvmCachePaths.size() > 1) {
+      XLOGF(INFO, "Configuring NVM cache: RAID-0 ({} devices) size {} MB",
+            config_.nvmCachePaths.size(), config_.nvmCacheSizeMB);
       // set up a software raid-0 across each nvm cache path.
       nvmConfig.navyConfig.setRaidFiles(config_.nvmCachePaths,
                                         config_.nvmCacheSizeMB * MB);
     } else {
       // use memory to mock NVM.
+      XLOGF(INFO, "Configuring NVM cache: memory file size {} MB",
+            config_.nvmCacheSizeMB);
       nvmConfig.navyConfig.setMemoryFile(config_.nvmCacheSizeMB * MB);
     }
     nvmConfig.navyConfig.setDeviceMetadataSize(config_.nvmCacheMetadataSizeMB *

cachelib/cachebench/runner/CacheStressor.h

@@ -98,8 +98,14 @@ class CacheStressor : public Stressor {
     }
     cacheConfig.nvmWriteBytesCallback =
         std::bind(&CacheStressor<Allocator>::getNvmBytesWritten, this);
-    cache_ = std::make_unique<CacheT>(cacheConfig, movingSync,
-                                      cacheConfig.cacheDir, config_.touchValue);
+    try {
+      cache_ = std::make_unique<CacheT>(
+          cacheConfig, movingSync, cacheConfig.cacheDir, config_.touchValue);
+    } catch (const std::exception& e) {
+      XLOG(INFO) << "Exception while creating cache: " << e.what();
+      throw;
+    }
+
     if (config_.opPoolDistribution.size() > cache_->numPools()) {
       throw std::invalid_argument(folly::sformat(
           "more pools specified in the test than in the cache. "