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mount: stop running the page-cache punch on Windows, where it is a no-op #120

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Merged
zcsizmadia merged 1 commit into from
Sep 13, 2026
Merged

mount: stop running the page-cache punch on Windows, where it is a no-op #120

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28 changes: 25 additions & 3 deletions src/mount/fuse_mount.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -617,9 +617,30 @@ Result<void> FuseMount::mount(const std::string& mountpoint, bool writeback, boo
// kernel has dropped the pages, and doing that on RemoteRoot's reader thread
// would stall every other reply behind it.
//
// The 981ms-to-5ms figure is a libfuse measurement; WinFsp showed no
// difference from the page-cache change either way, so this costs nothing
// measurable there and is left on for both.
// Linux only, because on Windows there is nothing to punch with.
// WinFsp-FUSE's fuse_invalidate_path is a stub — inc/fuse3/fuse.h, unchanged
// from v2.0 through master:
//
// FSP_FUSE_SYM(
// int fuse3_invalidate_path(struct fuse3 *f, const char *path),
// {
// (void)f;
// (void)path;
// return -ENOENT;
// })
//
// winfsp_fuse.h maps that spelling onto the standard one and FSP_FUSE_SYM
// expands to `static inline`, so the call never leaves the translation unit,
// never reaches the DLL, and invalidates nothing. An earlier version of this
// comment recorded that WinFsp "showed no difference from the page-cache
// change either way" and concluded it was free there. The measurement was
// right and the conclusion was wrong: it is free because it does nothing.
//
// So Direction A gets a thread and a queue that exist only to call a no-op a
// few thousand times per burst. Skip both, and stop implying a coherence
// mechanism is running there when none is. What WinFsp does offer is a mount
// option, -o FileInfoTimeout / -o DirInfoTimeout; see #88.
#ifndef _WIN32
{
std::lock_guard lock(inval_mu_);
inval_stop_ = false;
Expand All @@ -646,6 +667,7 @@ Result<void> FuseMount::mount(const std::string& mountpoint, bool writeback, boo
}
notify_.post(changes);
});
#endif // !_WIN32

loop_ = std::thread([this] {
// Deliberately single-threaded. fuse_loop_mt() has been measured against
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