issue-1751: [Filestore] WriteBackCache: Replace ReadWriteRangeLock with pinning mechanism, move remaining code to TUtils

Author: Andrei Nasonov

cloud/filestore/libs/vfs_fuse/write_back_cache/node_state.h

@@ -1,13 +1,13 @@
 #pragma once
 
 #include "node_cache.h"
-#include "read_write_range_lock.h"
 
 #include <cloud/filestore/public/api/protos/data.pb.h>
 
 #include <library/cpp/threading/future/core/future.h>
 
 #include <util/generic/deque.h>
+#include <util/generic/set.h>
 
 namespace NCloud::NFileStore::NFuse::NWriteBackCache {
 
@@ -51,16 +51,15 @@ struct TNodeState
     // Tracks cached data parts
     TNodeCache Cache;
 
-    // Prevent from concurrent read and write requests with overlapping ranges
-    TReadWriteRangeLock RangeLock;
-
-    ENodeFlushStatus FlushStatus = ENodeFlushStatus::NothingToFlush;
+    // Prevents flushed requests from being evicted from Cache
+    TMultiSet<ui64> CachedDataPins;
 
     // Flush requests are fulfilled when there are no pending or unflushed
     // requests with SequenceId less or equal than |TFlushRequest::SequenceId|.
     // Flush requests are stored in chronological order: SequenceId values are
     // strictly increasing so newer flush requests have larger SequenceId.
     TDeque<TFlushRequest> FlushRequests;
+    ENodeFlushStatus FlushStatus = ENodeFlushStatus::NothingToFlush;
 
     // Cached data extends the node size but until the data is flushed,
     // the changes are not visible to the tablet. FileSystem requests that
@@ -70,7 +69,7 @@ struct TNodeState
 
     bool CanBeDeleted() const
     {
-        if (Cache.Empty() && RangeLock.Empty()) {
+        if (Cache.Empty() && CachedDataPins.empty()) {
             Y_ABORT_UNLESS(FlushRequests.empty());
             Y_ABORT_UNLESS(FlushStatus == ENodeFlushStatus::NothingToFlush);
             return true;