enhance: Only keep atime if needed

- For the --recompress case, only reset timestamps if mtime has changed
  since local cache LRU cleanup always uses mtime.
- For the --trim-dir/--trim-recompress case, always reset timestamps
  since atime may be used for LRU cleanup.

4 files changed, 14 insertions, 6 deletions

diff --git a/src/core/FileRecompressor.cpp b/src/core/FileRecompressor.cpp
index 03818b01..131a85f9 100644
--- a/src/core/FileRecompressor.cpp
+++ b/src/core/FileRecompressor.cpp
@@ -29,7 +29,8 @@ namespace core {
 
 int64_t
 FileRecompressor::recompress(const std::string& cache_file,
-                             const std::optional<int8_t> level)
+                             std::optional<int8_t> level,
+                             KeepAtime keep_atime)
 {
   core::CacheEntry::Header header(cache_file);
 
@@ -59,7 +60,9 @@ FileRecompressor::recompress(const std::string& cache_file,
   }
 
   // Restore mtime/atime to keep cache LRU cleanup working as expected:
-  util::set_timestamps(cache_file, old_stat.mtime(), old_stat.atime());
+  if (keep_atime == KeepAtime::yes || new_stat) {
+    util::set_timestamps(cache_file, old_stat.mtime(), old_stat.atime());
+  }
 
   m_content_size += header.entry_size;
   m_old_size += old_stat.size_on_disk();
diff --git a/src/core/FileRecompressor.hpp b/src/core/FileRecompressor.hpp
index 289b0d75..b2fdb131 100644
--- a/src/core/FileRecompressor.hpp
+++ b/src/core/FileRecompressor.hpp
@@ -29,11 +29,14 @@ namespace core {
 class FileRecompressor
 {
 public:
+  enum class KeepAtime { yes, no };
+
   FileRecompressor() = default;
 
   // Returns on-disk size change in KiB.
   int64_t recompress(const std::string& cache_file,
-                     const std::optional<int8_t> level);
+                     const std::optional<int8_t> level,
+                     KeepAtime keep_atime);
 
   uint64_t content_size() const;
   uint64_t old_size() const;
diff --git a/src/core/mainoptions.cpp b/src/core/mainoptions.cpp
index a1866b5c..7b3e639a 100644
--- a/src/core/mainoptions.cpp
+++ b/src/core/mainoptions.cpp
@@ -316,7 +316,9 @@ trim_dir(const std::string& dir,
     for (const auto& file : files) {
       thread_pool.enqueue([&] {
         try {
-          recompressor.recompress(file.path, *recompress_level);
+          recompressor.recompress(file.path,
+                                  *recompress_level,
+                                  core::FileRecompressor::KeepAtime::yes);
         } catch (core::Error&) {
           // Ignore for now.
           incompressible_size += file.stat.size_on_disk();
diff --git a/src/storage/local/LocalStorage_compress.cpp b/src/storage/local/LocalStorage_compress.cpp
index 4aa587ad..81caa40b 100644
--- a/src/storage/local/LocalStorage_compress.cpp
+++ b/src/storage/local/LocalStorage_compress.cpp
@@ -110,8 +110,8 @@ LocalStorage::recompress(const std::optional<int8_t> level,
           thread_pool.enqueue(
             [&recompressor, &incompressible_size, level, stats_file, file] {
               try {
-                int64_t size_change_kibibyte =
-                  recompressor.recompress(file.path(), level);
+                int64_t size_change_kibibyte = recompressor.recompress(
+                  file.path(), level, core::FileRecompressor::KeepAtime::no);
                 StatsFile(stats_file).update([=](auto& cs) {
                   cs.increment(core::Statistic::cache_size_kibibyte,
                                size_change_kibibyte);