From 3b05f434fbc8423f6a82acb10c61a6168e7e7aab Mon Sep 17 00:00:00 2001
From: Vitaliy Filippov <vitalif@yourcmc.ru>
Date: Fri, 6 Oct 2023 21:05:14 +0300
Subject: [PATCH] Slightly split buffer eviction code

---
 internal/goofys.go | 134 ++++++++++++++++++++++++++-------------------
 1 file changed, 79 insertions(+), 55 deletions(-)

diff --git a/internal/goofys.go b/internal/goofys.go
index f35588eb..ca4204d7 100644
--- a/internal/goofys.go
+++ b/internal/goofys.go
@@ -566,15 +566,12 @@ func (fs *Goofys) FreeSomeCleanBuffers(origSize int64) (int64, bool) {
 		if inode == nil {
 			continue
 		}
-		toFs := -1
 		inode.mu.Lock()
-		del := -1
-		i := 0
-		for ; i < len(inode.buffers); i++ {
+		toFs := -1
+		inode.buffers = filterBuffers(inode.buffers, func(buf, prev *FileBuffer) FilterAction {
 			if freed >= size {
-				break
+				return FA_STOP
 			}
-			buf := inode.buffers[i]
 			// Never evict buffers flushed in an incomplete (last) part
 			if buf.dirtyID == 0 || buf.state == BUF_FLUSHED_FULL {
 				if buf.ptr != nil && !inode.IsRangeLocked(buf.offset, buf.length, false) &&
@@ -582,30 +579,7 @@ func (fs *Goofys) FreeSomeCleanBuffers(origSize int64) (int64, bool) {
 					(skipRecent == 0 || buf.recency <= skipRecent) &&
 					// Do not evict modified header
 					(buf.state != BUF_FLUSHED_FULL || buf.offset >= fs.flags.PartSizes[0].PartSize) {
-					if fs.flags.CachePath != "" && !buf.onDisk {
-						if toFs == -1 {
-							toFs = 0
-							if fs.lfru.GetHits(inode.Id) >= fs.flags.CacheToDiskHits {
-								toFs = 1
-							}
-						}
-						if toFs > 0 {
-							// Evict to disk
-							err := inode.OpenCacheFD()
-							if err != nil {
-								toFs = 0
-							} else {
-								_, err := inode.DiskCacheFD.WriteAt(buf.data, int64(buf.offset))
-								if err != nil {
-									toFs = 0
-									log.Errorf("Couldn't write %v bytes at offset %v to %v: %v",
-										len(buf.data), buf.offset, fs.flags.CachePath+"/"+inode.FullName(), err)
-								} else {
-									buf.onDisk = true
-								}
-							}
-						}
-					}
+					fs.tryEvictToDisk(inode, buf, &toFs)
 					// Release memory
 					buf.ptr.refs--
 					if buf.ptr.refs == 0 {
@@ -615,27 +589,17 @@ func (fs *Goofys) FreeSomeCleanBuffers(origSize int64) (int64, bool) {
 					buf.ptr = nil
 					buf.data = nil
 					if buf.dirtyID == 0 && !buf.onDisk {
-						if del == -1 {
-							del = i
-						}
-						continue
+						return FA_DEL
 					} else if buf.state == BUF_FLUSHED_FULL {
 						// A flushed buffer can be removed at a cost of finalizing multipart upload
 						// to read it back later. However it's likely not a problem if we're uploading
 						// a large file because we may never need to read it back.
 						// One exception is that we don't do it with the header because various
 						// software commonly modifies header after writing the whole large file
-						prev := del-1
-						if prev < 0 {
-							prev = i-1
-						}
-						if prev >= 0 && inode.buffers[prev].state == BUF_FL_CLEARED &&
-							buf.offset == (inode.buffers[prev].offset + inode.buffers[prev].length) {
-							inode.buffers[prev].length += buf.length
-							if del == -1 {
-								del = i
-							}
-							continue
+						if prev != nil && prev.state == BUF_FL_CLEARED &&
+							buf.offset == (prev.offset + prev.length) {
+							prev.length += buf.length
+							return FA_DEL
 						} else {
 							buf.state = BUF_FL_CLEARED
 						}
@@ -644,16 +608,8 @@ func (fs *Goofys) FreeSomeCleanBuffers(origSize int64) (int64, bool) {
 			} else if inode.fs.partNum(buf.offset+buf.length-1) != inode.fs.partNum(inode.lastWriteEnd) {
 				haveDirty = true
 			}
-			if del >= 0 {
-				inode.buffers = append(inode.buffers[0 : del], inode.buffers[i : ]...)
-				i = del
-				del = -1
-			}
-		}
-		if del >= 0 {
-			inode.buffers = append(inode.buffers[0 : del], inode.buffers[i : ]...)
-			del = -1
-		}
+			return FA_LEAVE
+		})
 		inode.mu.Unlock()
 		if freed >= size {
 			break
@@ -669,6 +625,74 @@ func (fs *Goofys) FreeSomeCleanBuffers(origSize int64) (int64, bool) {
 	return freed, haveDirty
 }
 
+func (fs *Goofys) tryEvictToDisk(inode *Inode, buf *FileBuffer, toFs *int) {
+	if fs.flags.CachePath != "" && !buf.onDisk {
+		if *toFs == -1 {
+			*toFs = 0
+			if fs.lfru.GetHits(inode.Id) >= fs.flags.CacheToDiskHits {
+				*toFs = 1
+			}
+		}
+		if *toFs > 0 {
+			// Evict to disk
+			err := inode.OpenCacheFD()
+			if err != nil {
+				*toFs = 0
+			} else {
+				_, err := inode.DiskCacheFD.WriteAt(buf.data, int64(buf.offset))
+				if err != nil {
+					*toFs = 0
+					log.Errorf("Couldn't write %v bytes at offset %v to %v: %v",
+						len(buf.data), buf.offset, fs.flags.CachePath+"/"+inode.FullName(), err)
+				} else {
+					buf.onDisk = true
+				}
+			}
+		}
+	}
+}
+
+type FilterAction uint8
+
+const (
+	FA_LEAVE FilterAction = 1
+	FA_DEL   FilterAction = 2
+	FA_STOP  FilterAction = 3
+)
+
+func filterBuffers(buffers []*FileBuffer, cb func(buf, prev *FileBuffer) FilterAction) []*FileBuffer {
+	del := -1
+	i := 0
+	var prev *FileBuffer
+	for ; i < len(buffers); i++ {
+		buf := buffers[i]
+		action := cb(buf, prev)
+		if action == FA_DEL {
+			if del == -1 {
+				if i >= 0 {
+					prev = buffers[i-1]
+				}
+				del = i
+			}
+		} else {
+			if del >= 0 {
+				buffers = append(buffers[0 : del], buffers[i : ]...)
+				i = del
+				del = -1
+			}
+			prev = buf
+		}
+		if action == FA_STOP {
+			break
+		}
+	}
+	if del >= 0 {
+		buffers = append(buffers[0 : del], buffers[i : ]...)
+		del = -1
+	}
+	return buffers
+}
+
 func (fs *Goofys) WakeupFlusherAndWait(wait bool) {
 	fs.flusherMu.Lock()
 	if fs.flushPending == 0 {