diff --git a/Documentation/config/core.adoc b/Documentation/config/core.adoc
index 9bc9de29d9..80dcc4b004 100644
--- a/Documentation/config/core.adoc
+++ b/Documentation/config/core.adoc
@@ -710,6 +710,12 @@ relatively high IO latencies.  When enabled, Git will do the
 index comparison to the filesystem data in parallel, allowing
 overlapping IO's.  Defaults to true.
 
+core.fscache::
+	Enable additional caching of file system data for some operations.
++
+Git for Windows uses this to bulk-read and cache lstat data of entire
+directories (instead of doing lstat file by file).
+
 core.unsetenvvars::
 	Windows-only: comma-separated list of environment variables'
 	names that need to be unset before spawning any other process.
diff --git a/builtin/add.c b/builtin/add.c
index 32709794b3..25add8da96 100644
--- a/builtin/add.c
+++ b/builtin/add.c
@@ -493,6 +493,10 @@ int cmd_add(int argc,
 	die_in_unpopulated_submodule(repo->index, prefix);
 	die_path_inside_submodule(repo->index, &pathspec);
 
+	enable_fscache(1);
+	/* We do not really re-read the index but update the up-to-date flags */
+	preload_index(repo->index, &pathspec, 0);
+
 	if (add_new_files) {
 		int baselen;
 
@@ -605,5 +609,6 @@ finish:
 	free(ps_matched);
 	dir_clear(&dir);
 	clear_pathspec(&pathspec);
+	enable_fscache(0);
 	return exit_status;
 }
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 0ba4f03f2e..a3da5a736a 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -415,6 +415,7 @@ static int checkout_worktree(const struct checkout_opts *opts,
 	if (pc_workers > 1)
 		init_parallel_checkout();
 
+	enable_fscache(1);
 	for (pos = 0; pos < the_repository->index->cache_nr; pos++) {
 		struct cache_entry *ce = the_repository->index->cache[pos];
 		if (ce->ce_flags & CE_MATCHED) {
@@ -440,6 +441,7 @@ static int checkout_worktree(const struct checkout_opts *opts,
 		errs |= run_parallel_checkout(&state, pc_workers, pc_threshold,
 					      NULL, NULL);
 	mem_pool_discard(&ce_mem_pool, should_validate_cache_entries());
+	enable_fscache(0);
 	remove_marked_cache_entries(the_repository->index, 1);
 	remove_scheduled_dirs();
 	errs |= finish_delayed_checkout(&state, opts->show_progress);
diff --git a/builtin/commit.c b/builtin/commit.c
index 8e901fe8db..24eb8e5a21 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -1623,6 +1623,7 @@ struct repository *repo UNUSED)
 		       PATHSPEC_PREFER_FULL,
 		       prefix, argv);
 
+	enable_fscache(1);
 	if (status_format != STATUS_FORMAT_PORCELAIN &&
 	    status_format != STATUS_FORMAT_PORCELAIN_V2)
 		progress_flag = REFRESH_PROGRESS;
diff --git a/compat/mingw-posix.h b/compat/mingw-posix.h
index da934834a1..1a917890b1 100644
--- a/compat/mingw-posix.h
+++ b/compat/mingw-posix.h
@@ -338,6 +338,17 @@ static inline int getrlimit(int resource, struct rlimit *rlp)
 	return 0;
 }
 
+/*
+ * The unit of FILETIME is 100-nanoseconds since January 1, 1601, UTC.
+ * Returns the 100-nanoseconds ("hekto nanoseconds") since the epoch.
+ */
+static inline long long filetime_to_hnsec(const FILETIME *ft)
+{
+	long long winTime = ((long long)ft->dwHighDateTime << 32) + ft->dwLowDateTime;
+	/* Windows to Unix Epoch conversion */
+	return winTime - 116444736000000000LL;
+}
+
 /*
  * Use mingw specific stat()/lstat()/fstat() implementations on Windows,
  * including our own struct stat with 64 bit st_size and nanosecond-precision
@@ -354,6 +365,13 @@ struct timespec {
 #endif
 #endif
 
+static inline void filetime_to_timespec(const FILETIME *ft, struct timespec *ts)
+{
+	long long hnsec = filetime_to_hnsec(ft);
+	ts->tv_sec = (time_t)(hnsec / 10000000);
+	ts->tv_nsec = (hnsec % 10000000) * 100;
+}
+
 struct mingw_stat {
     _dev_t st_dev;
     _ino_t st_ino;
@@ -386,7 +404,7 @@ int mingw_fstat(int fd, struct stat *buf);
 #ifdef lstat
 #undef lstat
 #endif
-#define lstat mingw_lstat
+extern int (*lstat)(const char *file_name, struct stat *buf);
 
 
 int mingw_utime(const char *file_name, const struct utimbuf *times);
diff --git a/compat/mingw.c b/compat/mingw.c
index 98fc8ff074..a2c8afe671 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -274,6 +274,7 @@ enum hide_dotfiles_type {
 
 static enum hide_dotfiles_type hide_dotfiles = HIDE_DOTFILES_DOTGITONLY;
 static char *unset_environment_variables;
+int core_fscache;
 
 int mingw_core_config(const char *var, const char *value,
 		      const struct config_context *ctx UNUSED,
@@ -287,6 +288,11 @@ int mingw_core_config(const char *var, const char *value,
 		return 0;
 	}
 
+	if (!strcmp(var, "core.fscache")) {
+		core_fscache = git_config_bool(var, value);
+		return 0;
+	}
+
 	if (!strcmp(var, "core.unsetenvvars")) {
 		if (!value)
 			return config_error_nonbool(var);
@@ -1058,24 +1064,6 @@ int mingw_chmod(const char *filename, int mode)
 	return _wchmod(wfilename, mode);
 }
 
-/*
- * The unit of FILETIME is 100-nanoseconds since January 1, 1601, UTC.
- * Returns the 100-nanoseconds ("hekto nanoseconds") since the epoch.
- */
-static inline long long filetime_to_hnsec(const FILETIME *ft)
-{
-	long long winTime = ((long long)ft->dwHighDateTime << 32) + ft->dwLowDateTime;
-	/* Windows to Unix Epoch conversion */
-	return winTime - 116444736000000000LL;
-}
-
-static inline void filetime_to_timespec(const FILETIME *ft, struct timespec *ts)
-{
-	long long hnsec = filetime_to_hnsec(ft);
-	ts->tv_sec = (time_t)(hnsec / 10000000);
-	ts->tv_nsec = (hnsec % 10000000) * 100;
-}
-
 /**
  * Verifies that safe_create_leading_directories() would succeed.
  */
@@ -1268,6 +1256,8 @@ int mingw_lstat(const char *file_name, struct stat *buf)
 	return -1;
 }
 
+int (*lstat)(const char *file_name, struct stat *buf) = mingw_lstat;
+
 static int get_file_info_by_handle(HANDLE hnd, struct stat *buf)
 {
 	BY_HANDLE_FILE_INFORMATION fdata;
diff --git a/compat/mingw.h b/compat/mingw.h
index 6ea53ee0d2..65df57d2a7 100644
--- a/compat/mingw.h
+++ b/compat/mingw.h
@@ -1,5 +1,7 @@
 #include "mingw-posix.h"
 
+extern int core_fscache;
+
 struct config_context;
 int mingw_core_config(const char *var, const char *value,
 		      const struct config_context *ctx, void *cb);
diff --git a/compat/win32/dirent.c b/compat/win32/dirent.c
index 24ee9b814d..f17e159546 100644
--- a/compat/win32/dirent.c
+++ b/compat/win32/dirent.c
@@ -1,15 +1,21 @@
 #include "../../git-compat-util.h"
 
-struct DIR {
-	struct dirent dd_dir; /* includes d_type */
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wpedantic"
+typedef struct dirent_DIR {
+	struct DIR base_dir;  /* extend base struct DIR */
 	HANDLE dd_handle;     /* FindFirstFile handle */
 	int dd_stat;          /* 0-based index */
-};
+	struct dirent dd_dir; /* includes d_type */
+} dirent_DIR;
+#pragma GCC diagnostic pop
+
+DIR *(*opendir)(const char *dirname) = dirent_opendir;
 
 static inline void finddata2dirent(struct dirent *ent, WIN32_FIND_DATAW *fdata)
 {
-	/* convert UTF-16 name to UTF-8 */
-	xwcstoutf(ent->d_name, fdata->cFileName, sizeof(ent->d_name));
+	/* convert UTF-16 name to UTF-8 (d_name points to dirent_DIR.dd_name) */
+	xwcstoutf(ent->d_name, fdata->cFileName, MAX_PATH * 3);
 
 	/* Set file type, based on WIN32_FIND_DATA */
 	if ((fdata->dwFileAttributes & FILE_ATTRIBUTE_REPARSE_POINT)
@@ -21,41 +27,7 @@ static inline void finddata2dirent(struct dirent *ent, WIN32_FIND_DATAW *fdata)
 		ent->d_type = DT_REG;
 }
 
-DIR *opendir(const char *name)
-{
-	wchar_t pattern[MAX_PATH + 2]; /* + 2 for '/' '*' */
-	WIN32_FIND_DATAW fdata;
-	HANDLE h;
-	int len;
-	DIR *dir;
-
-	/* convert name to UTF-16 and check length < MAX_PATH */
-	if ((len = xutftowcs_path(pattern, name)) < 0)
-		return NULL;
-
-	/* append optional '/' and wildcard '*' */
-	if (len && !is_dir_sep(pattern[len - 1]))
-		pattern[len++] = '/';
-	pattern[len++] = '*';
-	pattern[len] = 0;
-
-	/* open find handle */
-	h = FindFirstFileW(pattern, &fdata);
-	if (h == INVALID_HANDLE_VALUE) {
-		DWORD err = GetLastError();
-		errno = (err == ERROR_DIRECTORY) ? ENOTDIR : err_win_to_posix(err);
-		return NULL;
-	}
-
-	/* initialize DIR structure and copy first dir entry */
-	dir = xmalloc(sizeof(DIR));
-	dir->dd_handle = h;
-	dir->dd_stat = 0;
-	finddata2dirent(&dir->dd_dir, &fdata);
-	return dir;
-}
-
-struct dirent *readdir(DIR *dir)
+static struct dirent *dirent_readdir(dirent_DIR *dir)
 {
 	if (!dir) {
 		errno = EBADF; /* No set_errno for mingw */
@@ -82,7 +54,7 @@ struct dirent *readdir(DIR *dir)
 	return &dir->dd_dir;
 }
 
-int closedir(DIR *dir)
+static int dirent_closedir(dirent_DIR *dir)
 {
 	if (!dir) {
 		errno = EBADF;
@@ -93,3 +65,39 @@ int closedir(DIR *dir)
 	free(dir);
 	return 0;
 }
+
+DIR *dirent_opendir(const char *name)
+{
+	wchar_t pattern[MAX_PATH + 2]; /* + 2 for '/' '*' */
+	WIN32_FIND_DATAW fdata;
+	HANDLE h;
+	int len;
+	dirent_DIR *dir;
+
+	/* convert name to UTF-16 and check length < MAX_PATH */
+	if ((len = xutftowcs_path(pattern, name)) < 0)
+		return NULL;
+
+	/* append optional '/' and wildcard '*' */
+	if (len && !is_dir_sep(pattern[len - 1]))
+		pattern[len++] = '/';
+	pattern[len++] = '*';
+	pattern[len] = 0;
+
+	/* open find handle */
+	h = FindFirstFileW(pattern, &fdata);
+	if (h == INVALID_HANDLE_VALUE) {
+		DWORD err = GetLastError();
+		errno = (err == ERROR_DIRECTORY) ? ENOTDIR : err_win_to_posix(err);
+		return NULL;
+	}
+
+	/* initialize DIR structure and copy first dir entry */
+	dir = xmalloc(sizeof(dirent_DIR) + MAX_PATH);
+	dir->base_dir.preaddir = (struct dirent *(*)(DIR *dir)) dirent_readdir;
+	dir->base_dir.pclosedir = (int (*)(DIR *dir)) dirent_closedir;
+	dir->dd_handle = h;
+	dir->dd_stat = 0;
+	finddata2dirent(&dir->dd_dir, &fdata);
+	return (DIR*) dir;
+}
diff --git a/compat/win32/dirent.h b/compat/win32/dirent.h
index 058207e4bf..a58a8075fd 100644
--- a/compat/win32/dirent.h
+++ b/compat/win32/dirent.h
@@ -1,20 +1,34 @@
 #ifndef DIRENT_H
 #define DIRENT_H
 
-typedef struct DIR DIR;
-
 #define DT_UNKNOWN 0
 #define DT_DIR     1
 #define DT_REG     2
 #define DT_LNK     3
 
 struct dirent {
-	unsigned char d_type;      /* file type to prevent lstat after readdir */
-	char d_name[MAX_PATH * 3]; /* file name (* 3 for UTF-8 conversion) */
+	unsigned char d_type; /* file type to prevent lstat after readdir */
+	char d_name[/* FLEX_ARRAY */]; /* file name */
 };
 
-DIR *opendir(const char *dirname);
-struct dirent *readdir(DIR *dir);
-int closedir(DIR *dir);
+/*
+ * Base DIR structure, contains pointers to readdir/closedir implementations so
+ * that opendir may choose a concrete implementation on a call-by-call basis.
+ */
+typedef struct DIR {
+	struct dirent *(*preaddir)(struct DIR *dir);
+	int (*pclosedir)(struct DIR *dir);
+} DIR;
+
+/* default dirent implementation */
+extern DIR *dirent_opendir(const char *dirname);
+
+#define opendir git_opendir
+
+/* current dirent implementation */
+extern DIR *(*opendir)(const char *dirname);
+
+#define readdir(dir) (dir->preaddir(dir))
+#define closedir(dir) (dir->pclosedir(dir))
 
 #endif /* DIRENT_H */
diff --git a/compat/win32/fscache.c b/compat/win32/fscache.c
new file mode 100644
index 0000000000..2f489ced89
--- /dev/null
+++ b/compat/win32/fscache.c
@@ -0,0 +1,601 @@
+#include "../../git-compat-util.h"
+#include "../../hashmap.h"
+#include "../win32.h"
+#include "fscache.h"
+#include "../../dir.h"
+#include "../../abspath.h"
+#include "../../trace.h"
+#include "config.h"
+
+static int initialized;
+static volatile long enabled;
+static struct hashmap map;
+static CRITICAL_SECTION mutex;
+static unsigned int lstat_requests;
+static unsigned int opendir_requests;
+static unsigned int fscache_requests;
+static unsigned int fscache_misses;
+static struct trace_key trace_fscache = TRACE_KEY_INIT(FSCACHE);
+
+/*
+ * An entry in the file system cache. Used for both entire directory listings
+ * and file entries.
+ */
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wpedantic"
+struct fsentry {
+	struct hashmap_entry ent;
+	mode_t st_mode;
+	/* Pointer to the directory listing, or NULL for the listing itself. */
+	struct fsentry *list;
+	/* Pointer to the next file entry of the list. */
+	struct fsentry *next;
+
+	union {
+		/* Reference count of the directory listing. */
+		volatile long refcnt;
+		/* Handle to wait on the loading thread. */
+		HANDLE hwait;
+		struct {
+			/* More stat members (only used for file entries). */
+			off64_t st_size;
+			struct timespec st_atim;
+			struct timespec st_mtim;
+			struct timespec st_ctim;
+		} s;
+	} u;
+
+	/* Length of name. */
+	unsigned short len;
+	/*
+	 * Name of the entry. For directory listings: relative path of the
+	 * directory, without trailing '/' (empty for cwd()). For file entries:
+	 * name of the file. Typically points to the end of the structure if
+	 * the fsentry is allocated on the heap (see fsentry_alloc), or to a
+	 * local variable if on the stack (see fsentry_init).
+	 */
+	struct dirent dirent;
+};
+#pragma GCC diagnostic pop
+
+#pragma GCC diagnostic push
+#ifdef __clang__
+#pragma GCC diagnostic ignored "-Wflexible-array-extensions"
+#endif
+struct heap_fsentry {
+	union {
+		struct fsentry ent;
+		char dummy[sizeof(struct fsentry) + MAX_PATH];
+	} u;
+};
+#pragma GCC diagnostic pop
+
+/*
+ * Compares the paths of two fsentry structures for equality.
+ */
+static int fsentry_cmp(void *cmp_data UNUSED,
+		       const struct fsentry *fse1, const struct fsentry *fse2,
+		       void *keydata UNUSED)
+{
+	int res;
+	if (fse1 == fse2)
+		return 0;
+
+	/* compare the list parts first */
+	if (fse1->list != fse2->list &&
+	    (res = fsentry_cmp(NULL, fse1->list ? fse1->list : fse1,
+			       fse2->list ? fse2->list	: fse2, NULL)))
+		return res;
+
+	/* if list parts are equal, compare len and name */
+	if (fse1->len != fse2->len)
+		return fse1->len - fse2->len;
+	return fspathncmp(fse1->dirent.d_name, fse2->dirent.d_name, fse1->len);
+}
+
+/*
+ * Calculates the hash code of an fsentry structure's path.
+ */
+static unsigned int fsentry_hash(const struct fsentry *fse)
+{
+	unsigned int hash = fse->list ? fse->list->ent.hash : 0;
+	return hash ^ memihash(fse->dirent.d_name, fse->len);
+}
+
+/*
+ * Initialize an fsentry structure for use by fsentry_hash and fsentry_cmp.
+ */
+static void fsentry_init(struct fsentry *fse, struct fsentry *list,
+			 const char *name, size_t len)
+{
+	fse->list = list;
+	if (len > MAX_PATH)
+		BUG("Trying to allocate fsentry for long path '%.*s'",
+		    (int)len, name);
+	memcpy(fse->dirent.d_name, name, len);
+	fse->dirent.d_name[len] = 0;
+	fse->len = len;
+	hashmap_entry_init(&fse->ent, fsentry_hash(fse));
+}
+
+/*
+ * Allocate an fsentry structure on the heap.
+ */
+static struct fsentry *fsentry_alloc(struct fsentry *list, const char *name,
+		size_t len)
+{
+	/* overallocate fsentry and copy the name to the end */
+	struct fsentry *fse = xmalloc(sizeof(struct fsentry) + len + 1);
+	/* init the rest of the structure */
+	fsentry_init(fse, list, name, len);
+	fse->next = NULL;
+	fse->u.refcnt = 1;
+	return fse;
+}
+
+/*
+ * Add a reference to an fsentry.
+ */
+inline static void fsentry_addref(struct fsentry *fse)
+{
+	if (fse->list)
+		fse = fse->list;
+
+	InterlockedIncrement(&(fse->u.refcnt));
+}
+
+/*
+ * Release the reference to an fsentry, frees the memory if its the last ref.
+ */
+static void fsentry_release(struct fsentry *fse)
+{
+	if (fse->list)
+		fse = fse->list;
+
+	if (InterlockedDecrement(&(fse->u.refcnt)))
+		return;
+
+	while (fse) {
+		struct fsentry *next = fse->next;
+		free(fse);
+		fse = next;
+	}
+}
+
+/*
+ * Allocate and initialize an fsentry from a WIN32_FIND_DATA structure.
+ */
+static struct fsentry *fseentry_create_entry(struct fsentry *list,
+					     const WIN32_FIND_DATAW *fdata)
+{
+	char buf[MAX_PATH * 3];
+	int len;
+	struct fsentry *fse;
+	len = xwcstoutf(buf, fdata->cFileName, ARRAY_SIZE(buf));
+
+	fse = fsentry_alloc(list, buf, len);
+
+	fse->st_mode = file_attr_to_st_mode(fdata->FileAttributes,
+					    fdata->EaSize);
+	fse->dirent.d_type = S_ISREG(fse->st_mode) ? DT_REG :
+			S_ISDIR(fse->st_mode) ? DT_DIR : DT_LNK;
+	fse->u.s.st_size = (((off64_t) (fdata->nFileSizeHigh)) << 32)
+			| fdata->nFileSizeLow;
+	filetime_to_timespec(&(fdata->ftLastAccessTime), &(fse->u.s.st_atim));
+	filetime_to_timespec(&(fdata->ftLastWriteTime), &(fse->u.s.st_mtim));
+	filetime_to_timespec(&(fdata->ftCreationTime), &(fse->u.s.st_ctim));
+
+	return fse;
+}
+
+/*
+ * Create an fsentry-based directory listing (similar to opendir / readdir).
+ * Dir should not contain trailing '/'. Use an empty string for the current
+ * directory (not "."!).
+ */
+static struct fsentry *fsentry_create_list(const struct fsentry *dir,
+					   int *dir_not_found)
+{
+	wchar_t pattern[MAX_PATH + 2]; /* + 2 for '/' '*' */
+	WIN32_FIND_DATAW fdata;
+	HANDLE h;
+	int wlen;
+	struct fsentry *list, **phead;
+	DWORD err;
+
+	*dir_not_found = 0;
+
+	/* convert name to UTF-16 and check length < MAX_PATH */
+	if ((wlen = xutftowcsn(pattern, dir->dirent.d_name, MAX_PATH,
+			       dir->len)) < 0) {
+		if (errno == ERANGE)
+			errno = ENAMETOOLONG;
+		return NULL;
+	}
+
+	/* append optional '/' and wildcard '*' */
+	if (wlen)
+		pattern[wlen++] = '/';
+	pattern[wlen++] = '*';
+	pattern[wlen] = 0;
+
+	/* open find handle */
+	h = FindFirstFileExW(pattern, FindExInfoBasic, &fdata, FindExSearchNameMatch,
+		NULL, FIND_FIRST_EX_LARGE_FETCH);
+	if (h == INVALID_HANDLE_VALUE) {
+		err = GetLastError();
+		*dir_not_found = 1; /* or empty directory */
+		errno = (err == ERROR_DIRECTORY) ? ENOTDIR : err_win_to_posix(err);
+		trace_printf_key(&trace_fscache, "fscache: error(%d) '%s'\n",
+						 errno, dir->dirent.d_name);
+		return NULL;
+	}
+
+	/* allocate object to hold directory listing */
+	list = fsentry_alloc(NULL, dir->dirent.d_name, dir->len);
+	list->st_mode = S_IFDIR;
+	list->dirent.d_type = DT_DIR;
+
+	/* walk directory and build linked list of fsentry structures */
+	phead = &list->next;
+	do {
+		*phead = fseentry_create_entry(list, &fdata);
+		phead = &(*phead)->next;
+	} while (FindNextFileW(h, &fdata));
+
+	/* remember result of last FindNextFile, then close find handle */
+	err = GetLastError();
+	FindClose(h);
+
+	/* return the list if we've got all the files */
+	if (err == ERROR_NO_MORE_FILES)
+		return list;
+
+	/* otherwise free the list and return error */
+	fsentry_release(list);
+	errno = err_win_to_posix(err);
+	return NULL;
+}
+
+/*
+ * Adds a directory listing to the cache.
+ */
+static void fscache_add(struct fsentry *fse)
+{
+	if (fse->list)
+		fse = fse->list;
+
+	for (; fse; fse = fse->next)
+		hashmap_add(&map, &fse->ent);
+}
+
+/*
+ * Clears the cache.
+ */
+static void fscache_clear(void)
+{
+	hashmap_clear_and_free(&map, struct fsentry, ent);
+	hashmap_init(&map, (hashmap_cmp_fn)fsentry_cmp, NULL, 0);
+	lstat_requests = opendir_requests = 0;
+	fscache_misses = fscache_requests = 0;
+}
+
+/*
+ * Checks if the cache is enabled for the given path.
+ */
+int fscache_enabled(const char *path)
+{
+	return enabled > 0 && !is_absolute_path(path);
+}
+
+/*
+ * Looks up a cache entry, waits if its being loaded by another thread.
+ * The mutex must be owned by the calling thread.
+ */
+static struct fsentry *fscache_get_wait(struct fsentry *key)
+{
+	struct fsentry *fse = hashmap_get_entry(&map, key, ent, NULL);
+
+	/* return if its a 'real' entry (future entries have refcnt == 0) */
+	if (!fse || fse->list || fse->u.refcnt)
+		return fse;
+
+	/* create an event and link our key to the future entry */
+	key->u.hwait = CreateEvent(NULL, TRUE, FALSE, NULL);
+	key->next = fse->next;
+	fse->next = key;
+
+	/* wait for the loading thread to signal us */
+	LeaveCriticalSection(&mutex);
+	WaitForSingleObject(key->u.hwait, INFINITE);
+	CloseHandle(key->u.hwait);
+	EnterCriticalSection(&mutex);
+
+	/* repeat cache lookup */
+	return hashmap_get_entry(&map, key, ent, NULL);
+}
+
+/*
+ * Looks up or creates a cache entry for the specified key.
+ */
+static struct fsentry *fscache_get(struct fsentry *key)
+{
+	struct fsentry *fse, *future, *waiter;
+	int dir_not_found;
+
+	EnterCriticalSection(&mutex);
+	fscache_requests++;
+	/* check if entry is in cache */
+	fse = fscache_get_wait(key);
+	if (fse) {
+		if (fse->st_mode)
+			fsentry_addref(fse);
+		else
+			fse = NULL; /* non-existing directory */
+		LeaveCriticalSection(&mutex);
+		return fse;
+	}
+	/* if looking for a file, check if directory listing is in cache */
+	if (!fse && key->list) {
+		fse = fscache_get_wait(key->list);
+		if (fse) {
+			LeaveCriticalSection(&mutex);
+			/*
+			 * dir entry without file entry, or dir does not
+			 * exist -> file doesn't exist
+			 */
+			errno = ENOENT;
+			return NULL;
+		}
+	}
+
+	/* add future entry to indicate that we're loading it */
+	future = key->list ? key->list : key;
+	future->next = NULL;
+	future->u.refcnt = 0;
+	hashmap_add(&map, &future->ent);
+
+	/* create the directory listing (outside mutex!) */
+	LeaveCriticalSection(&mutex);
+	fse = fsentry_create_list(future, &dir_not_found);
+	EnterCriticalSection(&mutex);
+
+	/* remove future entry and signal waiting threads */
+	hashmap_remove(&map, &future->ent, NULL);
+	waiter = future->next;
+	while (waiter) {
+		HANDLE h = waiter->u.hwait;
+		waiter = waiter->next;
+		SetEvent(h);
+	}
+
+	/* leave on error (errno set by fsentry_create_list) */
+	if (!fse) {
+		if (dir_not_found && key->list) {
+			/*
+			 * Record that the directory does not exist (or is
+			 * empty, which for all practical matters is the same
+			 * thing as far as fscache is concerned).
+			 */
+			fse = fsentry_alloc(key->list->list,
+					    key->list->dirent.d_name,
+					    key->list->len);
+			fse->st_mode = 0;
+			hashmap_add(&map, &fse->ent);
+		}
+		LeaveCriticalSection(&mutex);
+		return NULL;
+	}
+
+	/* add directory listing to the cache */
+	fscache_misses++;
+	fscache_add(fse);
+
+	/* lookup file entry if requested (fse already points to directory) */
+	if (key->list)
+		fse = hashmap_get_entry(&map, key, ent, NULL);
+
+	if (fse && !fse->st_mode)
+		fse = NULL; /* non-existing directory */
+
+	/* return entry or ENOENT */
+	if (fse)
+		fsentry_addref(fse);
+	else
+		errno = ENOENT;
+
+	LeaveCriticalSection(&mutex);
+	return fse;
+}
+
+/*
+ * Enables or disables the cache. Note that the cache is read-only, changes to
+ * the working directory are NOT reflected in the cache while enabled.
+ */
+int fscache_enable(int enable)
+{
+	int result;
+
+	if (!initialized) {
+		int fscache = git_env_bool("GIT_TEST_FSCACHE", -1);
+
+		/* allow the cache to be disabled entirely */
+		if (fscache != -1)
+			core_fscache = fscache;
+		if (!core_fscache)
+			return 0;
+
+		InitializeCriticalSection(&mutex);
+		lstat_requests = opendir_requests = 0;
+		fscache_misses = fscache_requests = 0;
+		hashmap_init(&map, (hashmap_cmp_fn) fsentry_cmp, NULL, 0);
+		initialized = 1;
+	}
+
+	result = enable ? InterlockedIncrement(&enabled)
+			: InterlockedDecrement(&enabled);
+
+	if (enable && result == 1) {
+		/* redirect opendir and lstat to the fscache implementations */
+		opendir = fscache_opendir;
+		lstat = fscache_lstat;
+	} else if (!enable && !result) {
+		/* reset opendir and lstat to the original implementations */
+		opendir = dirent_opendir;
+		lstat = mingw_lstat;
+		EnterCriticalSection(&mutex);
+		trace_printf_key(&trace_fscache, "fscache: lstat %u, opendir %u, "
+						 "total requests/misses %u/%u\n",
+				lstat_requests, opendir_requests,
+				fscache_requests, fscache_misses);
+		fscache_clear();
+		LeaveCriticalSection(&mutex);
+	}
+	trace_printf_key(&trace_fscache, "fscache: enable(%d)\n", enable);
+	return result;
+}
+
+/*
+ * Flush cached stats result when fscache is enabled.
+ */
+void fscache_flush(void)
+{
+	if (enabled) {
+		EnterCriticalSection(&mutex);
+		fscache_clear();
+		LeaveCriticalSection(&mutex);
+	}
+}
+
+/*
+ * Lstat replacement, uses the cache if enabled, otherwise redirects to
+ * mingw_lstat.
+ */
+int fscache_lstat(const char *filename, struct stat *st)
+{
+	int dirlen, base, len;
+#pragma GCC diagnostic push
+#ifdef __clang__
+#pragma GCC diagnostic ignored "-Wflexible-array-extensions"
+#endif
+	struct heap_fsentry key[2];
+#pragma GCC diagnostic pop
+	struct fsentry *fse;
+
+	if (!fscache_enabled(filename))
+		return mingw_lstat(filename, st);
+
+	lstat_requests++;
+	/* split filename into path + name */
+	len = strlen(filename);
+	if (len && is_dir_sep(filename[len - 1]))
+		len--;
+	base = len;
+	while (base && !is_dir_sep(filename[base - 1]))
+		base--;
+	dirlen = base ? base - 1 : 0;
+
+	/* lookup entry for path + name in cache */
+	fsentry_init(&key[0].u.ent, NULL, filename, dirlen);
+	fsentry_init(&key[1].u.ent, &key[0].u.ent, filename + base, len - base);
+	fse = fscache_get(&key[1].u.ent);
+	if (!fse) {
+		errno = ENOENT;
+		return -1;
+	}
+
+	/*
+	 * Special case symbolic links: FindFirstFile()/FindNextFile() did not
+	 * provide us with the length of the target path.
+	 */
+	if (fse->u.s.st_size == MAX_PATH && S_ISLNK(fse->st_mode)) {
+		char buf[MAX_LONG_PATH];
+		int len = readlink(filename, buf, sizeof(buf) - 1);
+
+		if (len > 0)
+			fse->u.s.st_size = len;
+	}
+
+	/* copy stat data */
+	st->st_ino = 0;
+	st->st_gid = 0;
+	st->st_uid = 0;
+	st->st_dev = 0;
+	st->st_rdev = 0;
+	st->st_nlink = 1;
+	st->st_mode = fse->st_mode;
+	st->st_size = fse->u.s.st_size;
+	st->st_atim = fse->u.s.st_atim;
+	st->st_mtim = fse->u.s.st_mtim;
+	st->st_ctim = fse->u.s.st_ctim;
+
+	/* don't forget to release fsentry */
+	fsentry_release(fse);
+	return 0;
+}
+
+typedef struct fscache_DIR {
+	struct DIR base_dir; /* extend base struct DIR */
+	struct fsentry *pfsentry;
+	struct dirent *dirent;
+} fscache_DIR;
+
+/*
+ * Readdir replacement.
+ */
+static struct dirent *fscache_readdir(DIR *base_dir)
+{
+	fscache_DIR *dir = (fscache_DIR*) base_dir;
+	struct fsentry *next = dir->pfsentry->next;
+	if (!next)
+		return NULL;
+	dir->pfsentry = next;
+	dir->dirent = &next->dirent;
+	return dir->dirent;
+}
+
+/*
+ * Closedir replacement.
+ */
+static int fscache_closedir(DIR *base_dir)
+{
+	fscache_DIR *dir = (fscache_DIR*) base_dir;
+	fsentry_release(dir->pfsentry);
+	free(dir);
+	return 0;
+}
+
+/*
+ * Opendir replacement, uses a directory listing from the cache if enabled,
+ * otherwise calls original dirent implementation.
+ */
+DIR *fscache_opendir(const char *dirname)
+{
+	struct heap_fsentry key;
+	struct fsentry *list;
+	fscache_DIR *dir;
+	int len;
+
+	if (!fscache_enabled(dirname))
+		return dirent_opendir(dirname);
+
+	opendir_requests++;
+	/* prepare name (strip trailing '/', replace '.') */
+	len = strlen(dirname);
+	if ((len == 1 && dirname[0] == '.') ||
+	    (len && is_dir_sep(dirname[len - 1])))
+		len--;
+
+	/* get directory listing from cache */
+	fsentry_init(&key.u.ent, NULL, dirname, len);
+	list = fscache_get(&key.u.ent);
+	if (!list)
+		return NULL;
+
+	/* alloc and return DIR structure */
+	dir = (fscache_DIR*) xmalloc(sizeof(fscache_DIR));
+	dir->base_dir.preaddir = fscache_readdir;
+	dir->base_dir.pclosedir = fscache_closedir;
+	dir->pfsentry = list;
+	return (DIR*) dir;
+}
diff --git a/compat/win32/fscache.h b/compat/win32/fscache.h
new file mode 100644
index 0000000000..2f06f8df97
--- /dev/null
+++ b/compat/win32/fscache.h
@@ -0,0 +1,16 @@
+#ifndef FSCACHE_H
+#define FSCACHE_H
+
+int fscache_enable(int enable);
+#define enable_fscache(x) fscache_enable(x)
+
+int fscache_enabled(const char *path);
+#define is_fscache_enabled(path) fscache_enabled(path)
+
+void fscache_flush(void);
+#define flush_fscache() fscache_flush()
+
+DIR *fscache_opendir(const char *dir);
+int fscache_lstat(const char *file_name, struct stat *buf);
+
+#endif
diff --git a/config.mak.uname b/config.mak.uname
index a429da8797..94b12f3121 100644
--- a/config.mak.uname
+++ b/config.mak.uname
@@ -509,7 +509,7 @@ endif
 		compat/win32/path-utils.o \
 		compat/win32/pthread.o compat/win32/syslog.o \
 		compat/win32/trace2_win32_process_info.o \
-		compat/win32/dirent.o
+		compat/win32/dirent.o compat/win32/fscache.o
 	COMPAT_CFLAGS = -D__USE_MINGW_ACCESS -DDETECT_MSYS_TTY \
 		-DENSURE_MSYSTEM_IS_SET="\"$(MSYSTEM)\"" -DMINGW_PREFIX="\"$(patsubst /%,%,$(MINGW_PREFIX))\"" \
 		-DNOGDI -DHAVE_STRING_H -Icompat -Icompat/regex -Icompat/win32 -DSTRIP_EXTENSION=\".exe\"
@@ -714,7 +714,7 @@ ifeq ($(uname_S),MINGW)
 		compat/win32/flush.o \
 		compat/win32/path-utils.o \
 		compat/win32/pthread.o compat/win32/syslog.o \
-		compat/win32/dirent.o
+		compat/win32/dirent.o compat/win32/fscache.o
 	BASIC_CFLAGS += -DWIN32
 	EXTLIBS += -lws2_32
 	GITLIBS += git.res
diff --git a/contrib/buildsystems/CMakeLists.txt b/contrib/buildsystems/CMakeLists.txt
index fe26cebdab..7be6a0a7fc 100644
--- a/contrib/buildsystems/CMakeLists.txt
+++ b/contrib/buildsystems/CMakeLists.txt
@@ -301,7 +301,8 @@ if(CMAKE_SYSTEM_NAME STREQUAL "Windows")
 		compat/win32/trace2_win32_process_info.c
 		compat/win32/dirent.c
 		compat/nedmalloc/nedmalloc.c
-		compat/strdup.c)
+		compat/strdup.c
+		compat/win32/fscache.c)
 	set(NO_UNIX_SOCKETS 1)
 
 elseif(CMAKE_SYSTEM_NAME STREQUAL "Linux")
diff --git a/dir.c b/dir.c
index b00821f294..186b8832db 100644
--- a/dir.c
+++ b/dir.c
@@ -1156,16 +1156,64 @@ static int add_patterns(const char *fname, const char *base, int baselen,
 	size_t size = 0;
 	char *buf;
 
-	if (flags & PATTERN_NOFOLLOW)
-		fd = open_nofollow(fname, O_RDONLY);
-	else
-		fd = open(fname, O_RDONLY);
-
-	if (fd < 0 || fstat(fd, &st) < 0) {
-		if (fd < 0)
-			warn_on_fopen_errors(fname);
+	/*
+	 * A performance optimization for status.
+	 *
+	 * During a status scan, git looks in each directory for a .gitignore
+	 * file before scanning the directory.  Since .gitignore files are not
+	 * that common, we can waste a lot of time looking for files that are
+	 * not there.  Fortunately, the fscache already knows if the directory
+	 * contains a .gitignore file, since it has already read the directory
+	 * and it already has the stat-data.
+	 *
+	 * If the fscache is enabled, use the fscache-lstat() interlude to see
+	 * if the file exists (in the fscache hash maps) before trying to open()
+	 * it.
+	 *
+	 * This causes problem when the .gitignore file is a symlink, because
+	 * we call lstat() rather than stat() on the symlnk and the resulting
+	 * stat-data is for the symlink itself rather than the target file.
+	 * We CANNOT use stat() here because the fscache DOES NOT install an
+	 * interlude for stat() and mingw_stat() always calls "open-fstat-close"
+	 * on the file and defeats the purpose of the optimization here.  Since
+	 * symlinks are even more rare than .gitignore files, we force a fstat()
+	 * after our open() to get stat-data for the target file.
+	 *
+	 * Since `clang`'s `-Wunreachable-code` mode is clever, it would figure
+	 * out that on non-Windows platforms, this `lstat()` is unreachable.
+	 * We do want to keep the conditional block for the sake of Windows,
+	 * though, so let's use the `NOT_CONSTANT()` trick to suppress that error.
+	 */
+	if (NOT_CONSTANT(is_fscache_enabled(fname))) {
+		if (lstat(fname, &st) < 0) {
+			fd = -1;
+		} else {
+			fd = open(fname, O_RDONLY);
+			if (fd < 0)
+				warn_on_fopen_errors(fname);
+			else if (S_ISLNK(st.st_mode) && fstat(fd, &st) < 0) {
+				warn_on_fopen_errors(fname);
+				close(fd);
+				fd = -1;
+			}
+		}
+	} else {
+		if (flags & PATTERN_NOFOLLOW)
+			fd = open_nofollow(fname, O_RDONLY);
 		else
-			close(fd);
+			fd = open(fname, O_RDONLY);
+
+		if (fd < 0 || fstat(fd, &st) < 0) {
+			if (fd < 0)
+				warn_on_fopen_errors(fname);
+			else {
+				close(fd);
+				fd = -1;
+			}
+		}
+	}
+
+	if (fd < 0) {
 		if (!istate)
 			return -1;
 		r = read_skip_worktree_file_from_index(istate, fname,
diff --git a/entry.c b/entry.c
index 7817aee362..5ab78ca884 100644
--- a/entry.c
+++ b/entry.c
@@ -411,6 +411,9 @@ static int write_entry(struct cache_entry *ce, char *path, struct conv_attrs *ca
 	}
 
 finish:
+	/* Flush cached lstat in fscache after writing to disk. */
+	flush_fscache();
+
 	if (state->refresh_cache) {
 		if (!fstat_done && lstat(ce->name, &st) < 0)
 			return error_errno("unable to stat just-written file %s",
diff --git a/fetch-pack.c b/fetch-pack.c
index 40316c9a34..9cf2b6967c 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -760,6 +760,7 @@ static void mark_complete_and_common_ref(struct fetch_negotiator *negotiator,
 	save_commit_buffer = 0;
 
 	trace2_region_enter("fetch-pack", "parse_remote_refs_and_find_cutoff", NULL);
+	enable_fscache(1);
 	for (ref = *refs; ref; ref = ref->next) {
 		struct commit *commit;
 
@@ -784,6 +785,7 @@ static void mark_complete_and_common_ref(struct fetch_negotiator *negotiator,
 		if (!cutoff || cutoff < commit->date)
 			cutoff = commit->date;
 	}
+	enable_fscache(0);
 	trace2_region_leave("fetch-pack", "parse_remote_refs_and_find_cutoff", NULL);
 
 	/*
diff --git a/git-compat-util.h b/git-compat-util.h
index ded8edb0e5..e3a2841289 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -162,9 +162,11 @@ static inline int is_xplatform_dir_sep(int c)
 /* pull in Windows compatibility stuff */
 #include "compat/win32/path-utils.h"
 #include "compat/mingw.h"
+#include "compat/win32/fscache.h"
 #elif defined(_MSC_VER)
 #include "compat/win32/path-utils.h"
 #include "compat/msvc.h"
+#include "compat/win32/fscache.h"
 #endif
 
 /* used on Mac OS X */
@@ -1050,6 +1052,29 @@ static inline int is_missing_file_error(int errno_)
 	return (errno_ == ENOENT || errno_ == ENOTDIR);
 }
 
+/*
+ * Enable/disable a read-only cache for file system data on platforms that
+ * support it.
+ *
+ * Implementing a live-cache is complicated and requires special platform
+ * support (inotify, ReadDirectoryChangesW...). enable_fscache shall be used
+ * to mark sections of git code that extensively read from the file system
+ * without modifying anything. Implementations can use this to cache e.g. stat
+ * data or even file content without the need to synchronize with the file
+ * system.
+ */
+#ifndef enable_fscache
+#define enable_fscache(x) /* noop */
+#endif
+
+#ifndef is_fscache_enabled
+#define is_fscache_enabled(path) (0)
+#endif
+
+#ifndef flush_fscache
+#define flush_fscache() /* noop */
+#endif
+
 int cmd_main(int, const char **);
 
 /*
diff --git a/meson.build b/meson.build
index c7f62875af..e6c2e592b4 100644
--- a/meson.build
+++ b/meson.build
@@ -1260,6 +1260,7 @@ elif host_machine.system() == 'windows'
     'compat/winansi.c',
     'compat/win32/dirent.c',
     'compat/win32/flush.c',
+    'compat/win32/fscache.c',
     'compat/win32/path-utils.c',
     'compat/win32/pthread.c',
     'compat/win32/syslog.c',
diff --git a/parallel-checkout.c b/parallel-checkout.c
index 0bf4bd6d4a..8fadb7c804 100644
--- a/parallel-checkout.c
+++ b/parallel-checkout.c
@@ -640,6 +640,7 @@ static void write_items_sequentially(struct checkout *state)
 {
 	size_t i;
 
+	flush_fscache();
 	for (i = 0; i < parallel_checkout.nr; i++) {
 		struct parallel_checkout_item *pc_item = &parallel_checkout.items[i];
 		write_pc_item(pc_item, state);
diff --git a/preload-index.c b/preload-index.c
index b222821b44..61e8f3a1f6 100644
--- a/preload-index.c
+++ b/preload-index.c
@@ -141,6 +141,7 @@ void preload_index(struct index_state *index,
 		pthread_mutex_init(&pd.mutex, NULL);
 	}
 
+	enable_fscache(1);
 	for (i = 0; i < threads; i++) {
 		struct thread_data *p = data+i;
 		int err;
@@ -176,6 +177,8 @@ void preload_index(struct index_state *index,
 
 	trace2_data_intmax("index", NULL, "preload/sum_lstat", t2_sum_lstat);
 	trace2_region_leave("index", "preload", NULL);
+
+	enable_fscache(0);
 }
 
 int repo_read_index_preload(struct repository *repo,
diff --git a/read-cache.c b/read-cache.c
index 0c07c3aef7..09566361b9 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1512,6 +1512,7 @@ int refresh_index(struct index_state *istate, unsigned int flags,
 	typechange_fmt = in_porcelain ? "T\t%s\n" : "%s: needs update\n";
 	added_fmt      = in_porcelain ? "A\t%s\n" : "%s: needs update\n";
 	unmerged_fmt   = in_porcelain ? "U\t%s\n" : "%s: needs merge\n";
+	enable_fscache(1);
 	/*
 	 * Use the multi-threaded preload_index() to refresh most of the
 	 * cache entries quickly then in the single threaded loop below,
@@ -1606,6 +1607,7 @@ int refresh_index(struct index_state *istate, unsigned int flags,
 	display_progress(progress, istate->cache_nr);
 	stop_progress(&progress);
 	trace_performance_leave("refresh index");
+	enable_fscache(0);
 	return has_errors;
 }
 
diff --git a/t/README b/t/README
index adbbd9acf4..f194681514 100644
--- a/t/README
+++ b/t/README
@@ -479,6 +479,9 @@ GIT_TEST_NAME_HASH_VERSION=<int>, when set, causes 'git pack-objects' to
 assume '--name-hash-version=<n>'.
 
 
+GIT_TEST_FSCACHE=<boolean> exercises the uncommon fscache code path
+which adds a cache below mingw's lstat and dirent implementations.
+
 Naming Tests
 ------------
 
diff --git a/t/t1090-sparse-checkout-scope.sh b/t/t1090-sparse-checkout-scope.sh
index 3a14218b24..529844e286 100755
--- a/t/t1090-sparse-checkout-scope.sh
+++ b/t/t1090-sparse-checkout-scope.sh
@@ -106,4 +106,24 @@ test_expect_success 'in partial clone, sparse checkout only fetches needed blobs
 	test_cmp expect actual
 '
 
+test_expect_success MINGW 'no unnecessary opendir() with fscache' '
+	git clone . fscache-test &&
+	(
+		cd fscache-test &&
+		git config core.fscache 1 &&
+		echo "/excluded/*" >.git/info/sparse-checkout &&
+		for f in $(test_seq 10)
+		do
+			sha1=$(echo $f | git hash-object -w --stdin) &&
+			git update-index --add \
+				--cacheinfo 100644,$sha1,excluded/$f || exit 1
+		done &&
+		test_tick &&
+		git commit -m excluded &&
+		GIT_TRACE_FSCACHE=1 git status >out 2>err &&
+		grep excluded err >grep.out &&
+		test_line_count = 1 grep.out
+	)
+'
+
 test_done
diff --git a/t/t7201-co.sh b/t/t7201-co.sh
index 9bcf7c0b40..545f388c44 100755
--- a/t/t7201-co.sh
+++ b/t/t7201-co.sh
@@ -35,6 +35,42 @@ fill () {
 }
 
 
+test_expect_success MINGW 'fscache flush cache' '
+
+	git init fscache-test &&
+	cd fscache-test &&
+	git config core.fscache 1 &&
+	echo A > test.txt &&
+	git add test.txt &&
+	git commit -m A &&
+	echo B >> test.txt &&
+	git checkout . &&
+	test -z "$(git status -s)" &&
+	echo A > expect.txt &&
+	test_cmp expect.txt test.txt &&
+	cd .. &&
+	rm -rf fscache-test
+'
+
+test_expect_success MINGW 'fscache flush cache dir' '
+
+	git init fscache-test &&
+	cd fscache-test &&
+	git config core.fscache 1 &&
+	echo A > test.txt &&
+	git add test.txt &&
+	git commit -m A &&
+	rm test.txt &&
+	mkdir test.txt &&
+	touch test.txt/test.txt &&
+	git checkout . &&
+	test -z "$(git status -s)" &&
+	echo A > expect.txt &&
+	test_cmp expect.txt test.txt &&
+	cd .. &&
+	rm -rf fscache-test
+'
+
 test_expect_success setup '
 	fill x y z >same &&
 	fill 1 2 3 4 5 6 7 8 >one &&
diff --git a/unpack-trees.c b/unpack-trees.c
index f38c761ab9..450dbdf7c1 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -1823,7 +1823,9 @@ static void mark_new_skip_worktree(struct pattern_list *pl,
 	 * 2. Widen worktree according to sparse-checkout file.
 	 * Matched entries will have skip_wt_flag cleared (i.e. "in")
 	 */
+	enable_fscache(istate->cache_nr);
 	clear_ce_flags(istate, select_flag, skip_wt_flag, pl, show_progress);
+	disable_fscache();
 }
 
 static void populate_from_existing_patterns(struct unpack_trees_options *o,