07/07: [NTOSKRNL] Replace the alloc map by a bitmap

[Pierre Schweitzer]

https://git.reactos.org/?p=reactos.git;a=commitdiff;h=f080ee13055509cc75096…

commit f080ee13055509cc75096d55c7d8f2913dbd585b
Author:     Pierre Schweitzer <pierre(a)reactos.org>
AuthorDate: Sat Aug 11 22:47:58 2018 +0200
Commit:     Pierre Schweitzer <pierre(a)reactos.org>
CommitDate: Sat Aug 11 23:01:12 2018 +0200

    [NTOSKRNL] Replace the alloc map by a bitmap
---
 ntoskrnl/mm/pagefile.c | 41 ++++++++++++++---------------------------
 1 file changed, 14 insertions(+), 27 deletions(-)

diff --git a/ntoskrnl/mm/pagefile.c b/ntoskrnl/mm/pagefile.c
index 196aeabb5b..d1c2e0c013 100644
--- a/ntoskrnl/mm/pagefile.c
+++ b/ntoskrnl/mm/pagefile.c
@@ -50,9 +50,8 @@ typedef struct _PAGINGFILE
     LARGE_INTEGER CurrentSize;
     PFN_NUMBER FreePages;
     PFN_NUMBER UsedPages;
-    PULONG AllocMap;
+    PRTL_BITMAP AllocMap;
     KSPIN_LOCK AllocMapLock;
-    ULONG AllocMapSize;
 }
 PAGINGFILE, *PPAGINGFILE;
 
@@ -297,27 +296,13 @@ static ULONG
 MiAllocPageFromPagingFile(PPAGINGFILE PagingFile)
 {
     KIRQL oldIrql;
-    ULONG i, j;
+    ULONG off;
 
     KeAcquireSpinLock(&PagingFile->AllocMapLock, &oldIrql);
-
-    for (i = 0; i < PagingFile->AllocMapSize; i++)
-    {
-        for (j = 0; j < 32; j++)
-        {
-            if (!(PagingFile->AllocMap[i] & (1 << j)))
-            {
-                PagingFile->AllocMap[i] |= (1 << j);
-                PagingFile->UsedPages++;
-                PagingFile->FreePages--;
-                KeReleaseSpinLock(&PagingFile->AllocMapLock, oldIrql);
-                return((i * 32) + j);
-            }
-        }
-    }
-
+    off = RtlFindClearBitsAndSet(PagingFile->AllocMap, 1, 0);
     KeReleaseSpinLock(&PagingFile->AllocMapLock, oldIrql);
-    return(0xFFFFFFFF);
+
+    return off;
 }
 
 VOID
@@ -338,7 +323,7 @@ MmFreeSwapPage(SWAPENTRY Entry)
     }
     KeAcquireSpinLockAtDpcLevel(&PagingFileList[i]->AllocMapLock);
 
-    PagingFileList[i]->AllocMap[off >> 5] &= (~(1 << (off % 32)));
+    RtlClearBit(PagingFileList[i]->AllocMap, off >> 5);
 
     PagingFileList[i]->FreePages++;
     PagingFileList[i]->UsedPages--;
@@ -661,11 +646,10 @@ NtCreatePagingFile(IN PUNICODE_STRING FileName,
     PagingFile->UsedPages = 0;
     KeInitializeSpinLock(&PagingFile->AllocMapLock);
 
-    AllocMapSize = (PagingFile->FreePages / 32) + 1;
-    PagingFile->AllocMap = ExAllocatePool(NonPagedPool,
-                                          AllocMapSize * sizeof(ULONG));
-    PagingFile->AllocMapSize = AllocMapSize;
-
+    AllocMapSize = sizeof(RTL_BITMAP) + (((PagingFile->FreePages + 31) / 32) *
sizeof(ULONG));
+    PagingFile->AllocMap = ExAllocatePoolWithTag(NonPagedPool,
+                                                 AllocMapSize,
+                                                 TAG_MM);
     if (PagingFile->AllocMap == NULL)
     {
         ExFreePool(PagingFile);
@@ -674,7 +658,10 @@ NtCreatePagingFile(IN PUNICODE_STRING FileName,
         return(STATUS_NO_MEMORY);
     }
 
-    RtlZeroMemory(PagingFile->AllocMap, AllocMapSize * sizeof(ULONG));
+    RtlInitializeBitMap(PagingFile->AllocMap,
+                        (PULONG)(PagingFile->AllocMap + 1),
+                        (ULONG)(PagingFile->FreePages));
+    RtlClearAllBits(PagingFile->AllocMap);
 
     KeAcquireSpinLock(&PagingFileListLock, &oldIrql);
     for (i = 0; i < MAX_PAGING_FILES; i++)