logtail: remove LowMemory mode

Fixes tailscale/tailscale#13685

logtail currently has a LowMemory flag, which is enabled upon initialization on memory-constrained platforms like iOS. This flag reduces the ring buffer size from 256 log lines to 64. It was introduced over four years ago, back when Tailscale supported iOS 14 and earlier, where network extensions were limited to 15 MB of RAM.

Since the memory limit has now increased to 50 MB on all supported iOS versions (with our minimum requirement being iOS 15.0), the need to conserve a few kilobytes of RAM by reducing buffer entries and the size of each flush is minimal.

The additional code paths are more things we need to maintain over time... with little benefit. This PR removes that.

To be merged after we cut the first 1.77 unstable, as this might be a risky change.

Signed-off-by: Andrea Gottardo <andrea@gottardo.me>

logtail/logtail.go

@@ -45,9 +45,6 @@ const maxSize = 256 << 10
 // Note that JSON log messages can be as large as maxSize.
 const maxTextSize = 16 << 10
 
-// lowMemRatio reduces maxSize and maxTextSize by this ratio in lowMem mode.
-const lowMemRatio = 4
-
 // bufferSize is the typical buffer size to retain.
 // It is large enough to handle most log messages,
 // but not too large to be a notable waste of memory if retained forever.
@@ -72,7 +69,6 @@ type Config struct {
 	BaseURL        string          // if empty defaults to "https://log.tailscale.io"
 	HTTPC          *http.Client    // if empty defaults to http.DefaultClient
 	SkipClientTime bool            // if true, client_time is not written to logs
-	LowMemory      bool            // if true, logtail minimizes memory use
 	Clock          tstime.Clock    // if set, Clock.Now substitutes uses of time.Now
 	Stderr         io.Writer       // if set, logs are sent here instead of os.Stderr
 	StderrLevel    int             // max verbosity level to write to stderr; 0 means the non-verbose messages only
@@ -118,11 +114,7 @@ func NewLogger(cfg Config, logf tslogger.Logf) *Logger {
 		cfg.Stderr = os.Stderr
 	}
 	if cfg.Buffer == nil {
-		pendingSize := 256
-		if cfg.LowMemory {
-			pendingSize = 64
-		}
-		cfg.Buffer = NewMemoryBuffer(pendingSize)
+		cfg.Buffer = NewMemoryBuffer(256)
 	}
 	var procID uint32
 	if cfg.IncludeProcID {
@@ -155,7 +147,6 @@ func NewLogger(cfg Config, logf tslogger.Logf) *Logger {
 		stderrLevel:    int64(cfg.StderrLevel),
 		httpc:          cfg.HTTPC,
 		url:            cfg.BaseURL + "/c/" + cfg.Collection + "/" + cfg.PrivateID.String() + urlSuffix,
-		lowMem:         cfg.LowMemory,
 		buffer:         cfg.Buffer,
 		skipClientTime: cfg.SkipClientTime,
 		drainWake:      make(chan struct{}, 1),
@@ -188,7 +179,6 @@ type Logger struct {
 	stderrLevel    int64 // accessed atomically
 	httpc          *http.Client
 	url            string
-	lowMem         bool
 	skipClientTime bool
 	netMonitor     *netmon.Monitor
 	buffer         Buffer
@@ -325,13 +315,6 @@ func (l *Logger) drainPending() (b []byte) {
 	}()
 
 	maxLen := maxSize
-	if l.lowMem {
-		// When operating in a low memory environment, it is better to upload
-		// in multiple operations than it is to allocate a large body and OOM.
-		// Even if maxLen is less than maxSize, we can still upload an entry
-		// that is up to maxSize if we happen to encounter one.
-		maxLen /= lowMemRatio
-	}
 	for len(b) < maxLen {
 		line, err := l.buffer.TryReadLine()
 		switch {
@@ -683,9 +666,6 @@ func (l *Logger) appendText(dst, src []byte, skipClientTime bool, procID uint32,
 	// Append the text string, which may be truncated.
 	// Invalid UTF-8 will be mangled with the Unicode replacement character.
 	max := maxTextSize
-	if l.lowMem {
-		max /= lowMemRatio
-	}
 	dst = append(dst, `"text":`...)
 	dst = appendTruncatedString(dst, src, max)
 	return append(dst, "}\n"...)