[lld] [lld][MachO] Follow-up to use madvise() for threaded file page-in. (PR #157917)

[John Holdsworth via llvm-commits]

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@@ -334,29 +338,37 @@ class SerialBackgroundQueue {
 // This code forces the page-ins on multiple threads so
 // the process is not stalled waiting on disk buffer i/o.
 void multiThreadedPageInBackground(DeferredFiles &deferred) {
+  using namespace std::chrono;
   static const size_t pageSize = Process::getPageSizeEstimate();
   static const size_t largeArchive = 10 * 1024 * 1024;
-#ifndef NDEBUG
-  using namespace std::chrono;
-  std::atomic_int numDeferedFilesTouched = 0;
   static std::atomic_uint64_t totalBytes = 0;
+  std::atomic_int numDeferedFilesAdvised = 0;
   auto t0 = high_resolution_clock::now();
-#endif
 
   auto preloadDeferredFile = [&](const DeferredFile &deferredFile) {
     const StringRef &buff = deferredFile.buffer.getBuffer();
     if (buff.size() > largeArchive)
       return;
-#ifndef NDEBUG
+    if (((uintptr_t)buff.data() & (pageSize - 1)))
+      return; // Not mmap()'d (not page aligned).
+
     totalBytes += buff.size();
-    numDeferedFilesTouched += 1;
-#endif
+    numDeferedFilesAdvised += 1;
 
+#if _WIN32
     // Reference all file's mmap'd pages to load them into memory.
     for (const char *page = buff.data(), *end = page + buff.size(); page < end;
          page += pageSize)
       LLVM_ATTRIBUTE_UNUSED volatile char t = *page;
+#else
+    if (madvise((void *)buff.data(), buff.size(), MADV_WILLNEED) < 0)
+#ifndef NDEBUG
+      llvm::errs() << "madvise() error " << strerror(errno)
+#endif
+          ;
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johnno1962 wrote:

I've pushed an amend to use LLVM_DEBUG().

https://github.com/llvm/llvm-project/pull/157917