From: Serge Gautherie <reactos-git_serge_fake@gautherie.fr>
Date: Wed, 12 Apr 2017 15:57:00 +0200
Subject: [IOMGR]
iomdl.c:
*Create/Use a LOOKASIDE_MDL_FIXED_SIZE define for IoAllocateMdl().
*Fix a few comments, especially in IoFreeMdl().
CORE-13066


Index: reactos/ntoskrnl/io/iomgr/iomdl.c
--- a/reactos/ntoskrnl/io/iomgr/iomdl.c
+++ b/reactos/ntoskrnl/io/iomgr/iomdl.c
@@ -14,6 +14,8 @@
 
 /* FUNCTIONS *****************************************************************/
 
+/* Internal fixed size for MDLs in lookaside list. */
+#define LOOKASIDE_MDL_FIXED_SIZE 23
 /*
  * @implemented
  */
@@ -37,9 +39,9 @@
 
     /* Calculate the number of pages for the allocation */
     Size = ADDRESS_AND_SIZE_TO_SPAN_PAGES(VirtualAddress, Length);
-    if (Size > 23)
+    if (Size > LOOKASIDE_MDL_FIXED_SIZE)
     {
-        /* This is bigger then our fixed-size MDLs. Calculate real size */
+        /* This is bigger than our fixed size MDLs. Calculate real size. */
         Size *= sizeof(PFN_NUMBER);
         Size += sizeof(MDL);
         if (Size > MAXUSHORT) return NULL;
@@ -47,7 +49,7 @@
     else
     {
         /* Use an internal fixed MDL size */
-        Size = (23 * sizeof(PFN_NUMBER)) + sizeof(MDL);
+        Size = (LOOKASIDE_MDL_FIXED_SIZE * sizeof(PFN_NUMBER)) + sizeof(MDL);
         Flags |= MDL_ALLOCATED_FIXED_SIZE;
 
         /* Allocate one from the lookaside list */
@@ -87,6 +89,7 @@
     /* Return the allocated mdl */
     return Mdl;
 }
+#undef LOOKASIDE_MDL_FIXED_SIZE
 
 /*
  * @implemented
@@ -148,15 +151,15 @@
     /* Tell Mm to reuse the MDL */
     MmPrepareMdlForReuse(Mdl);
 
-    /* Check if this was a pool allocation */
+    /* Always free fixed size allocations to the lookaside list. */
     if (!(Mdl->MdlFlags & MDL_ALLOCATED_FIXED_SIZE))
     {
-        /* Free it from the pool */
+        /* Free it to the pool. */
         ExFreePoolWithTag(Mdl, TAG_MDL);
     }
     else
     {
-        /* Free it from the lookaside */
+        /* Free it to the lookaside list. */
         IopFreeMdlFromLookaside(Mdl, LookasideMdlList);
     }
 }