diff options
| -rw-r--r-- | internal/fusefrontend/file.go | 33 | ||||
| -rw-r--r-- | internal/fusefrontend/write_lock.go | 8 |
2 files changed, 37 insertions, 4 deletions
diff --git a/internal/fusefrontend/file.go b/internal/fusefrontend/file.go index ee48930..9991f3e 100644 --- a/internal/fusefrontend/file.go +++ b/internal/fusefrontend/file.go @@ -9,6 +9,7 @@ import ( "log" "os" "sync" + "sync/atomic" "syscall" "time" @@ -43,6 +44,11 @@ type file struct { header *contentenc.FileHeader // go-fuse nodefs.loopbackFile loopbackFile nodefs.File + // Store what the last byte was written + lastWrittenOffset int64 + // The opCount is used to judge whether "lastWrittenOffset" is still + // guaranteed to be correct. + lastOpCount uint64 } // NewFile returns a new go-fuse File instance. @@ -282,6 +288,16 @@ func (f *file) doWrite(data []byte, off int64) (uint32, fuse.Status) { return written, status } +// isConsecutiveWrite returns true if the current write +// directly (in time and space) follows the last write. +// This is an optimisation for streaming writes on NFS where a +// Stat() call is very expensive. +// The caller must "wlock.lock(f.ino)" otherwise this check would be racy. +func (f *file) isConsecutiveWrite(off int64) bool { + opCount := atomic.LoadUint64(&wlock.opCount) + return opCount == f.lastOpCount+1 && off == f.lastWrittenOffset+1 +} + // Write - FUSE call // // If the write creates a hole, pads the file to the next block boundary. @@ -299,11 +315,20 @@ func (f *file) Write(data []byte, off int64) (uint32, fuse.Status) { defer wlock.unlock(f.ino) tlog.Debug.Printf("ino%d: FUSE Write: offset=%d length=%d", f.ino, off, len(data)) // If the write creates a file hole, we have to zero-pad the last block. - status := f.writePadHole(off) - if !status.Ok() { - return 0, status + // But if the write directly follows an earlier write, it cannot create a + // hole, and we can save one Stat() call. + if !f.isConsecutiveWrite(off) { + status := f.writePadHole(off) + if !status.Ok() { + return 0, status + } + } + n, status := f.doWrite(data, off) + if status.Ok() { + f.lastOpCount = atomic.LoadUint64(&wlock.opCount) + f.lastWrittenOffset = off + int64(len(data)) - 1 } - return f.doWrite(data, off) + return n, status } // Release - FUSE call, close file diff --git a/internal/fusefrontend/write_lock.go b/internal/fusefrontend/write_lock.go index 2f8ea4e..7394994 100644 --- a/internal/fusefrontend/write_lock.go +++ b/internal/fusefrontend/write_lock.go @@ -2,6 +2,7 @@ package fusefrontend import ( "sync" + "sync/atomic" ) func init() { @@ -20,6 +21,12 @@ var wlock wlockMap // 2) lock ... unlock ... // 3) unregister type wlockMap struct { + // Counts lock() calls. As every operation that modifies a file should + // call it, this effectively serves as a write-operation counter. + // The variable is accessed without holding any locks so atomic operations + // must be used. It must be the first element of the struct to guarantee + // 64-bit alignment. + opCount uint64 // Protects map access sync.Mutex inodeLocks map[uint64]*refCntMutex @@ -62,6 +69,7 @@ func (w *wlockMap) unregister(ino uint64) { // lock retrieves the entry for "ino" and locks it. func (w *wlockMap) lock(ino uint64) { + atomic.AddUint64(&w.opCount, 1) w.Lock() r := w.inodeLocks[ino] w.Unlock() |