From 557a6e78256144beb95a175e2d8a7106b01d16c9 Mon Sep 17 00:00:00 2001
From: "L. Pereira" <l@tia.mat.br>
Date: Sat, 24 Aug 2024 16:27:29 -0700
Subject: [PATCH] Use mincore(2) to queue an madvise(2) call if necessary

---
 CMakeLists.txt                      |  1 +
 src/cmake/lwan-build-config.h.cmake |  1 +
 src/lib/lwan-mod-serve-files.c      | 31 ++++++++++++++++++++++++++++-
 3 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index c1e913a75..461b18742 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -175,6 +175,7 @@ set(CMAKE_REQUIRED_LIBRARIES ${CMAKE_THREAD_LIBS_INIT})
 check_function_exists(get_current_dir_name LWAN_HAVE_GET_CURRENT_DIR_NAME)
 check_symbol_exists(reallocarray stdlib.h LWAN_HAVE_REALLOCARRAY)
 check_symbol_exists(eventfd sys/eventfd.h LWAN_HAVE_EVENTFD)
+check_symbol_exists(mincore sys/mman.h LWAN_HAVE_MINCORE)
 check_function_exists(mempcpy LWAN_HAVE_MEMPCPY)
 check_function_exists(memrchr LWAN_HAVE_MEMRCHR)
 check_function_exists(pipe2 LWAN_HAVE_PIPE2)
diff --git a/src/cmake/lwan-build-config.h.cmake b/src/cmake/lwan-build-config.h.cmake
index 6b50d454f..7cf31ab5f 100644
--- a/src/cmake/lwan-build-config.h.cmake
+++ b/src/cmake/lwan-build-config.h.cmake
@@ -49,6 +49,7 @@
 #cmakedefine LWAN_HAVE_SYSLOG
 #cmakedefine LWAN_HAVE_STPCPY
 #cmakedefine LWAN_HAVE_EVENTFD
+#cmakedefine LWAN_HAVE_MINCORE
 
 /* Compiler builtins for specific CPU instruction support */
 #cmakedefine LWAN_HAVE_BUILTIN_CLZLL
diff --git a/src/lib/lwan-mod-serve-files.c b/src/lib/lwan-mod-serve-files.c
index 2e88829d5..8a5bcc149 100644
--- a/src/lib/lwan-mod-serve-files.c
+++ b/src/lib/lwan-mod-serve-files.c
@@ -50,6 +50,10 @@
 #include <zstd.h>
 #endif
 
+#define MMAP_SIZE_THRESHOLD 16384
+#define MINCORE_CALL_THRESHOLD 10
+#define MINCORE_VEC_LEN(len) (((len) + PAGE_SIZE - 1) / PAGE_SIZE)
+
 static const struct lwan_key_value deflate_compression_hdr[] = {
     {"Content-Encoding", "deflate"}, {}
 };
@@ -113,6 +117,7 @@ struct mmap_cache_data {
 #if defined(LWAN_HAVE_ZSTD)
     struct lwan_value zstd;
 #endif
+    int mincore_call_threshold;
 };
 
 struct sendfile_cache_data {
@@ -544,6 +549,8 @@ static bool mmap_init(struct file_cache_entry *ce,
     ce->mime_type =
         lwan_determine_mime_type_for_file_name(full_path + priv->root_path_len);
 
+    md->mincore_call_threshold = MINCORE_CALL_THRESHOLD;
+
     return true;
 }
 
@@ -755,7 +762,7 @@ static const struct cache_funcs *get_funcs(struct serve_files_priv *priv,
 
     /* It's not a directory: choose the fastest way to serve the file
      * judging by its size. */
-    if (st->st_size < 16384)
+    if (st->st_size < MMAP_SIZE_THRESHOLD)
         return &mmap_funcs;
 
     return &sendfile_funcs;
@@ -1252,6 +1259,28 @@ static enum lwan_http_status mmap_serve(struct lwan_request *request,
         return serve_value_ok(request, fce->mime_type, to_serve,
                               compression_hdr);
 
+#ifdef LWAN_HAVE_MINCORE
+    if (md->mincore_call_threshold-- == 0) {
+        unsigned char mincore_vec[MINCORE_VEC_LEN(MMAP_SIZE_THRESHOLD)];
+
+        if (!mincore(to_serve->value, to_serve->len, mincore_vec)) {
+            const size_t pgs = MINCORE_VEC_LEN(to_serve->len);
+
+            for (size_t pg = 0; pg < pgs; pg++) {
+                if (mincore_vec[pg] & 0x01)
+                    continue;
+
+                /* FIXME: madvise only the page that's not in core */
+                lwan_madvise_queue(to_serve->value, to_serve->len);
+                coro_yield(request->conn->coro, CONN_CORO_WANT_WRITE);
+                break;
+            }
+        }
+
+        md->mincore_call_threshold = MINCORE_CALL_THRESHOLD;
+    }
+#endif
+
     off_t from, to;
     enum lwan_http_status status =
         compute_range(request, &from, &to, (off_t)to_serve->len);