4 files changed, 44 insertions, 12 deletions

diff --git a/sw/source/core/bastyp/swcache.cxx b/sw/source/core/bastyp/swcache.cxx
index ff6d568b8e83..64eb233b6bf7 100644
--- a/sw/source/core/bastyp/swcache.cxx
+++ b/sw/source/core/bastyp/swcache.cxx
@@ -436,6 +436,7 @@ bool SwCache::Insert( SwCacheObj *pNew )
 
 void SwCache::SetLRUOfst( const sal_uInt16 nOfst )
 {
+    assert(nOfst < m_nCurMax);
     if ( !m_pRealFirst || ((m_aCacheObjects.size() - m_aFreePositions.size()) < nOfst) )
         return;
 
diff --git a/sw/source/core/inc/swcache.hxx b/sw/source/core/inc/swcache.hxx
index 9a6563e256ba..00f33514ff39 100644
--- a/sw/source/core/inc/swcache.hxx
+++ b/sw/source/core/inc/swcache.hxx
@@ -117,15 +117,12 @@ public:
     sal_uInt16 size() { return m_aCacheObjects.size(); }
 };
 
-/// Safely manipulate the cache
+/// Try to prevent visible SwParaPortions from being deleted.
 class SwSaveSetLRUOfst
 {
-    SwCache &rCache;
 public:
-    SwSaveSetLRUOfst( SwCache &rC, const sal_uInt16 nOfst )
-        : rCache( rC )          { rCache.SetLRUOfst( nOfst );  }
-
-    ~SwSaveSetLRUOfst()         { rCache.ResetLRUOfst(); }
+    SwSaveSetLRUOfst();
+    ~SwSaveSetLRUOfst();
 };
 
 /**
diff --git a/sw/source/core/text/txtcache.cxx b/sw/source/core/text/txtcache.cxx
index b0f540a2a024..fcc8b434cdd8 100644
--- a/sw/source/core/text/txtcache.cxx
+++ b/sw/source/core/text/txtcache.cxx
@@ -21,6 +21,9 @@
 #include <txtfrm.hxx>
 #include "porlay.hxx"
 
+#include <sfx2/viewsh.hxx>
+#include <view.hxx>
+
 SwTextLine::SwTextLine( SwTextFrame const *pFrame, std::unique_ptr<SwParaPortion> pNew ) :
     SwCacheObj( static_cast<void const *>(pFrame) ),
     pLine( std::move(pNew) )
@@ -135,4 +138,37 @@ void SwTextFrame::SetPara( SwParaPortion *pNew, bool bDelete )
     }
 }
 
+/** Prevent the SwParaPortions of the *visible* paragraphs from being deleted;
+    they would just be recreated on the next paint.
+
+    Heuristic: 100 per view are visible
+
+    If the cache is too small, enlarge it to ensure there are sufficient free
+    entries for the layout so it doesn't have to throw away a node's
+    SwParaPortion when it starts formatting the next node.
+*/
+SwSaveSetLRUOfst::SwSaveSetLRUOfst()
+{
+    sal_uInt16 nVisibleShells(0);
+    for (auto pView = SfxViewShell::GetFirst(true, checkSfxViewShell<SwView>);
+         pView != nullptr;
+         pView = SfxViewShell::GetNext(*pView, true, checkSfxViewShell<SwView>))
+    {
+        ++nVisibleShells;
+    }
+
+    sal_uInt16 const nPreserved(100 * nVisibleShells);
+    SwCache & rCache(*SwTextFrame::GetTextCache());
+    if (rCache.GetCurMax() < nPreserved + 250)
+    {
+        rCache.IncreaseMax(nPreserved + 250 - rCache.GetCurMax());
+    }
+    rCache.SetLRUOfst(nPreserved);
+}
+
+SwSaveSetLRUOfst::~SwSaveSetLRUOfst()
+{
+    SwTextFrame::GetTextCache()->ResetLRUOfst();
+}
+
 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */
diff --git a/sw/source/core/view/viewsh.cxx b/sw/source/core/view/viewsh.cxx
index f8a805dad4a9..ae1bc40512d0 100644
--- a/sw/source/core/view/viewsh.cxx
+++ b/sw/source/core/view/viewsh.cxx
@@ -712,9 +712,8 @@ void SwViewShell::LayoutIdle()
 #endif
 
     {
-        //Prepare and recover cache, so that it will not get fouled.
-        SwSaveSetLRUOfst aSave( *SwTextFrame::GetTextCache(),
-                             SwTextFrame::GetTextCache()->GetCurMax() - 50 );
+        // Preserve top of the text frame cache.
+        SwSaveSetLRUOfst aSaveLRU;
         // #125243# there are lots of stacktraces indicating that Imp() returns NULL
         // this SwViewShell seems to be invalid - but it's not clear why
         // this return is only a workaround!
@@ -990,9 +989,8 @@ void SwViewShell::CalcLayout()
     SET_CURR_SHELL( this );
     SwWait aWait( *GetDoc()->GetDocShell(), true );
 
-    //prepare and recover cache, so that it will not get fouled.
-    SwSaveSetLRUOfst aSaveLRU( *SwTextFrame::GetTextCache(),
-                                  SwTextFrame::GetTextCache()->GetCurMax() - 50 );
+    // Preserve top of the text frame cache.
+    SwSaveSetLRUOfst aSaveLRU;
 
     //switch on Progress when none is running yet.
     const bool bEndProgress = SfxProgress::GetActiveProgress( GetDoc()->GetDocShell() ) == nullptr;