Resolve "Add dentry cache"

Marc Vefrequested to merge
marc/292-add-dentry-cache into master

This MR adds a directory entry cache for the client to avoid a huge number of stat calls after readdir, e.g., for ls -l type operations. It is experimental and thus disabled by default. Can be enabled via include/config.hpp or with the env variable LIBGKFS_DENTRY_CACHE=ON/OFF.

It works by using the extended_dir_entry RPC to receive some metadata along the the dentries from the daemons. This metadata is then placed into the cache and retrieved in a stat operation (for a cache miss, an RPC is sent with vanilla functionality). The cache is discarded upon close but can be changed via include/config.hpp. Note, this may cause semantical issues (removed files will remain in the cache forever).

The performance improvements are already noticeable locally for a couple 1000 files.

Depends on !195 (merged)

Closes #292 (closed)

Edited by Marc Vef

Merge request reports

include/client/CMakeLists.txt

+2 −0
Changes for include/client/CMakeLists.txt: 2 added lines, 0 removed lines.
Original line number Diff line number Diff line
@@ -42,6 +42,7 @@ target_sources( 
    preload.hpp

    preload_context.hpp

    preload_util.hpp

    cache.hpp

    rpc/rpc_types.hpp

    rpc/forward_management.hpp

    rpc/forward_metadata.hpp
@@ -68,6 +69,7 @@ target_sources( 
    preload.hpp

    preload_context.hpp

    preload_util.hpp

    cache.hpp

    rpc/rpc_types.hpp

    rpc/forward_management.hpp

    rpc/forward_metadata.hpp

include/client/cache.hpp

0 → 100644
+137 −0
Changes for include/client/cache.hpp: 137 added lines, 0 removed lines.
Original line number Diff line number Diff line 
/*

  Copyright 2018-2024, Barcelona Supercomputing Center (BSC), Spain

  Copyright 2015-2024, Johannes Gutenberg Universitaet Mainz, Germany



  This software was partially supported by the

  EC H2020 funded project NEXTGenIO (Project ID: 671951, www.nextgenio.eu).



  This software was partially supported by the

  ADA-FS project under the SPPEXA project funded by the DFG.



  This file is part of GekkoFS' POSIX interface.



  GekkoFS' POSIX interface is free software: you can redistribute it and/or

  modify it under the terms of the GNU Lesser General Public License as

  published by the Free Software Foundation, either version 3 of the License,

  or (at your option) any later version.



  GekkoFS' POSIX interface is distributed in the hope that it will be useful,

  but WITHOUT ANY WARRANTY; without even the implied warranty of

  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

  GNU Lesser General Public License for more details.



  You should have received a copy of the GNU Lesser General Public License

  along with GekkoFS' POSIX interface.  If not, see

  <https://www.gnu.org/licenses/>.



  SPDX-License-Identifier: LGPL-3.0-or-later

*/



#ifndef GKFS_CLIENT_CACHE

#define GKFS_CLIENT_CACHE



#include <client/open_file_map.hpp>



#include <ctime>

#include <functional>

#include <string>

#include <unordered_map>

#include <mutex>

#include <optional>

#include <cstdint>



namespace gkfs::cache {



namespace dir {



/**

 * @brief Cache entry metadata.

 * The entries are limited to the get_dir_extended RPC.

 */

struct cache_entry {

    gkfs::filemap::FileType file_type;

    uint64_t size;

    time_t ctime;

};



/**

 * @brief Cache for directory entries to accelerate ls -l type operations

 */

class DentryCache {

private:

    // <dir_id, <name, cache_entry>>: Associate a directory id with its entries

    // containing the directory name and cache entry metadata

    std::unordered_map<uint32_t, std::unordered_map<std::string, cache_entry>>

            entries_;

    // <dir_path, dir_id>: Associate a directory path with a unique id

    std::unordered_map<std::string, uint32_t> entry_dir_id_;

    std::mutex mtx_;                 // Mutex to protect the cache

    std::hash<std::string> str_hash; // hash to generate ids



    /**

     * @brief Generate a unique id for caching a directory

     * @param dir_path

     * @return id

     */

    uint32_t

    gen_dir_id(const std::string& dir_path);



    /**

     * @brief Get the unique id for a directory to retrieve its entries. Creates

     * an id if it does not exist.

     * @param dir_path

     * @return id

     */

    uint32_t

    get_dir_id(const std::string& dir_path);



public:

    DentryCache() = default;



    virtual ~DentryCache() = default;



    /**

     * @brief Insert a new entry in the cache

     * @param parent_dir

     * @param name

     * @param value

     */

    void

    insert(const std::string& parent_dir, std::string name, cache_entry value);



    /**

     * @brief Get an entry from the cache for a given directory

     * @param parent_dir

     * @param name

     * @return std::optional<cache_entry>

     */

    std::optional<cache_entry>

    get(const std::string& parent_dir, const std::string& name);



    /**

     * @brief Clear the cache for a given directory. Called when a directory is

     * closed

     * @param dir_path

     */

    void

    clear_dir(const std::string& dir_path);



    /**

     * @brief Dump the cache to the log for debugging purposes. Not used in

     * production.

     * @param dir_path

     */

    void

    dump_cache_to_log(const std::string& dir_path);



    /**

     * @brief Clear the entire cache

     */

    void

    clear();

};

} // namespace dir



} // namespace gkfs::cache



#endif // GKFS_CLIENT_CACHE

include/client/env.hpp

+1 −0
Changes for include/client/env.hpp: 1 added line, 0 removed lines.
Original line number Diff line number Diff line
@@ -60,6 +60,7 @@ static constexpr auto METRICS_IP_PORT = ADD_PREFIX("METRICS_IP_PORT"); 


static constexpr auto NUM_REPL = ADD_PREFIX("NUM_REPL");

static constexpr auto PROXY_PID_FILE = ADD_PREFIX("PROXY_PID_FILE");

static constexpr auto DENTRY_CACHE = ADD_PREFIX("DENTRY_CACHE");



} // namespace gkfs::env

include/client/preload_context.hpp

+21 −0
Changes for include/client/preload_context.hpp: 21 added lines, 0 removed lines.
Original line number Diff line number Diff line
@@ -55,6 +55,12 @@ namespace messagepack { 
class ClientMetrics;

}



namespace cache {

namespace dir {

class DentryCache;

}

} // namespace cache



namespace preload {

/*

 * Client file system config
@@ -90,6 +96,8 @@ private: 
    std::shared_ptr<gkfs::filemap::OpenFileMap> ofm_;

    std::shared_ptr<gkfs::rpc::Distributor> distributor_;

    std::shared_ptr<FsConfig> fs_conf_;

    std::shared_ptr<gkfs::cache::dir::DentryCache> dentry_cache_;

    bool use_dentry_cache_{false};



    std::string cwd_;

    std::vector<std::string> mountdir_components_;
@@ -229,6 +237,19 @@ public: 
    const std::shared_ptr<FsConfig>&

    fs_conf() const;



    std::shared_ptr<gkfs::cache::dir::DentryCache>

    dentry_cache() const;



    void

    dentry_cache(std::shared_ptr<gkfs::cache::dir::DentryCache> dentry_cache);



    bool

    use_dentry_cache() const;



    void

    use_dentry_cache(bool use_dentry_cache);





    void

    enable_interception();

include/common/CMakeLists.txt

+2 −2

File changed.

Contains only whitespace changes.