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0d634a1296
Summary: In support of making Eden's file access stateless, add a facade that connects the BlobCache and ObjectStore, allowing FileInode to fetch blobs, minimizing reloads and memory usage. Reviewed By: strager Differential Revision: D10850143 fbshipit-source-id: 4307f7c1143aecad1284ea3cadf3e4efca9a3925
73 lines
2.3 KiB
C++
73 lines
2.3 KiB
C++
/*
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* Copyright (c) 2018-present, Facebook, Inc.
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* All rights reserved.
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*
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* This source code is licensed under the BSD-style license found in the
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* LICENSE file in the root directory of this source tree. An additional grant
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* of patent rights can be found in the PATENTS file in the same directory.
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*
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*/
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#pragma once
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#include <folly/futures/Future.h>
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#include <memory>
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#include "eden/fs/store/BlobCache.h"
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namespace facebook {
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namespace eden {
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class Blob;
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class Hash;
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class IObjectStore;
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/**
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* File access in Eden is stateless - we do not receive notifications from the
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* kernel for open() and close(). However, it's inefficient to load blobs from
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* cache for every read() request that makes into the edenfs process. Thus,
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* centralize blob access through this interface.
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*
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* TODO: To support large files, they should be split into a series of blobs,
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* and those blobs should get their own blob IDs, which could then be used
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* in this API. Splitting large blobs into a series of smaller blobs has the
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* benefit of helping bound Eden's memory usage here.
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*/
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class BlobAccess {
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public:
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/**
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* Creates a new BlobAccess with specified cache parameters.
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*
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* - cacheSizeBytes attempts to restrict the number of blobs kept in memory to
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* the specified number of bytes.
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* - recentBlobCacheLength specifies how many recently-accessed blobs should
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* be kept around, even if they are larger than cacheSizeBytes. This is
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* important to avoid reloading large files.
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*/
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BlobAccess(
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std::shared_ptr<IObjectStore> objectStore,
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std::shared_ptr<BlobCache> blobCache);
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~BlobAccess();
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/**
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* Loads and returns the entire blob's contents.
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*
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* If the accessPolicy is NotNeededAgain, the associated blob will not be
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* cached.
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*
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* Returns both the blob and an interest handle from the BlobCache that can
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* be dropped when the blob is no longer needed.
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*/
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folly::Future<BlobCache::GetResult> getBlob(
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const Hash& hash,
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BlobCache::Interest interest = BlobCache::Interest::LikelyNeededAgain);
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private:
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BlobAccess(const BlobAccess&) = delete;
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BlobAccess& operator=(const BlobAccess&) = delete;
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const std::shared_ptr<IObjectStore> objectStore_;
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const std::shared_ptr<BlobCache> blobCache_;
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};
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} // namespace eden
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} // namespace facebook
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