Use 4K as the minimum segment size (#2452)

- This normalizes the behavior for kestrel no matter what memory pool implementation is used. The transports should behave the same (ask for 1/2 full blocks) across pool implementations.
- Declare the minimum segment size in KestrelMemoryPool
- Updated the AdaptedPipeline to use MinimumSegmentSize / 2

src/Kestrel.Core/Adapter/Internal/AdaptedPipeline.cs

@@ -3,15 +3,16 @@
 
 using System;
 using System.IO;
+using System.IO.Pipelines;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http;
-using System.IO.Pipelines;
+using Microsoft.AspNetCore.Server.Kestrel.Transport.Abstractions.Internal;
 
 namespace Microsoft.AspNetCore.Server.Kestrel.Core.Adapter.Internal
 {
     public class AdaptedPipeline : IDuplexPipe
     {
-        private const int MinAllocBufferSize = 2048;
+        private static readonly int MinAllocBufferSize = KestrelMemoryPool.MinimumSegmentSize / 2;
 
         private readonly IDuplexPipe _transport;
         private readonly IDuplexPipe _application;

src/Kestrel.Core/Internal/ConnectionDispatcher.cs

@@ -86,7 +86,8 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal
             writerScheduler: writerScheduler,
             pauseWriterThreshold: serviceContext.ServerOptions.Limits.MaxRequestBufferSize ?? 0,
             resumeWriterThreshold: serviceContext.ServerOptions.Limits.MaxRequestBufferSize ?? 0,
-            useSynchronizationContext: false
+            useSynchronizationContext: false,
+            minimumSegmentSize: KestrelMemoryPool.MinimumSegmentSize
         );
 
         internal static PipeOptions GetOutputPipeOptions(ServiceContext serviceContext, MemoryPool<byte> memoryPool, PipeScheduler readerScheduler) => new PipeOptions
@@ -96,7 +97,8 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal
             writerScheduler: serviceContext.Scheduler,
             pauseWriterThreshold: GetOutputResponseBufferSize(serviceContext),
             resumeWriterThreshold: GetOutputResponseBufferSize(serviceContext),
-            useSynchronizationContext: false
+            useSynchronizationContext: false,
+            minimumSegmentSize: KestrelMemoryPool.MinimumSegmentSize
         );
 
         private static long GetOutputResponseBufferSize(ServiceContext serviceContext)

src/Kestrel.Core/Internal/Http/HttpProtocol.cs

@@ -13,11 +13,12 @@ using System.Runtime.CompilerServices;
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
+using Microsoft.AspNetCore.Connections;
 using Microsoft.AspNetCore.Hosting.Server;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Http.Features;
-using Microsoft.AspNetCore.Connections;
 using Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Infrastructure;
+using Microsoft.AspNetCore.Server.Kestrel.Transport.Abstractions.Internal;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Primitives;
 
@@ -1340,7 +1341,8 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http
                 writerScheduler: PipeScheduler.Inline,
                 pauseWriterThreshold: 1,
                 resumeWriterThreshold: 1,
-                useSynchronizationContext: false
+                useSynchronizationContext: false,
+                minimumSegmentSize: KestrelMemoryPool.MinimumSegmentSize
             ));
     }
 }

src/Kestrel.Core/Internal/HttpConnection.cs

@@ -17,6 +17,7 @@ using Microsoft.AspNetCore.Server.Kestrel.Core.Features;
 using Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http;
 using Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http2;
 using Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Infrastructure;
+using Microsoft.AspNetCore.Server.Kestrel.Transport.Abstractions.Internal;
 using Microsoft.Extensions.Logging;
 
 namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal
@@ -78,7 +79,8 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal
             writerScheduler: PipeScheduler.Inline,
             pauseWriterThreshold: _context.ServiceContext.ServerOptions.Limits.MaxRequestBufferSize ?? 0,
             resumeWriterThreshold: _context.ServiceContext.ServerOptions.Limits.MaxRequestBufferSize ?? 0,
-            useSynchronizationContext: false
+            useSynchronizationContext: false,
+            minimumSegmentSize: KestrelMemoryPool.MinimumSegmentSize
         );
 
         internal PipeOptions AdaptedOutputPipeOptions => new PipeOptions
@@ -88,7 +90,8 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal
             writerScheduler: PipeScheduler.Inline,
             pauseWriterThreshold: _context.ServiceContext.ServerOptions.Limits.MaxResponseBufferSize ?? 0,
             resumeWriterThreshold: _context.ServiceContext.ServerOptions.Limits.MaxResponseBufferSize ?? 0,
-            useSynchronizationContext: false
+            useSynchronizationContext: false,
+            minimumSegmentSize: KestrelMemoryPool.MinimumSegmentSize
         );
 
         private IKestrelTrace Log => _context.ServiceContext.Log;

src/Kestrel.Transport.Abstractions/Internal/KestrelMemoryPool.cs

@@ -8,5 +8,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Transport.Abstractions.Internal
     public static class KestrelMemoryPool
     {
         public static MemoryPool<byte> Create() => new SlabMemoryPool();
+
+        public static readonly int MinimumSegmentSize = 4096;
     }
 }

src/Kestrel.Transport.Libuv/Internal/LibuvConnection.cs

@@ -16,7 +16,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Transport.Libuv.Internal
 {
     public partial class LibuvConnection : LibuvConnectionContext
     {
-        private const int MinAllocBufferSize = 2048;
+        private static readonly int MinAllocBufferSize = KestrelMemoryPool.MinimumSegmentSize / 2;
 
         private static readonly Action<UvStreamHandle, int, object> _readCallback =
             (handle, status, state) => ReadCallback(handle, status, state);

src/Kestrel.Transport.Sockets/Internal/SocketConnection.cs

@@ -18,8 +18,8 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets.Internal
 {
     internal sealed class SocketConnection : TransportConnection
     {
-        private const int MinAllocBufferSize = 2048;
+        private static readonly int MinAllocBufferSize = KestrelMemoryPool.MinimumSegmentSize / 2;
-        public readonly static bool IsWindows = RuntimeInformation.IsOSPlatform(OSPlatform.Windows);
+        private static readonly bool IsWindows = RuntimeInformation.IsOSPlatform(OSPlatform.Windows);
 
         private readonly Socket _socket;
         private readonly PipeScheduler _scheduler;