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Extract a few constants in PageList.
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@chrisvest
chrisvest committed Apr 27, 2018
1 parent 3340c3e commit df6a941
Showing 1 changed file with 32 additions and 23 deletions.
55 changes: 32 additions & 23 deletions community/io/src/main/java/org/neo4j/io/pagecache/impl/muninn/PageList.java
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Expand Up @@ -52,10 +52,19 @@ class PageList
{
private static final boolean forceSlowMemoryClear = flag( PageList.class, "forceSlowMemoryClear", false );

public static final int META_DATA_BYTES_PER_PAGE = 32;
public static final long MAX_PAGES = Integer.MAX_VALUE;
static final int META_DATA_BYTES_PER_PAGE = 32;
static final long MAX_PAGES = Integer.MAX_VALUE;

private static final int UNBOUND_LAST_MODIFIED_TX_ID = -1;
private static final long MASK_USAGE_COUNT = 0x07;
private static final long MASK_NOT_USAGE_COUNT = ~MASK_USAGE_COUNT;
private static final int MAX_USAGE_COUNT = 4;
private static final int MASK_NOT_FILE_PAGE_ID = 0xFFFFFF;
private static final int SHIFT_FILE_PAGE_ID = 24;
private static final int SHIFT_SWAPPER_ID = 3;
private static final long MASK_SHIFTED_SWAPPER_ID = 0b1_11111_11111_11111_11111;
private static final long MASK_NOT_SWAPPER_ID = ~(MASK_SHIFTED_SWAPPER_ID << SHIFT_SWAPPER_ID);
private static final long UNBOUND_PAGE_BINDING = PageCursor.UNBOUND_PAGE_ID << SHIFT_FILE_PAGE_ID;

// 40 bits for file page id
private static final long MAX_FILE_PAGE_ID = 0b11111111_11111111_11111111_11111111_11111111L;
Expand All @@ -68,6 +77,7 @@ class PageList
private static final int OFFSET_SWAPPER_ID = 29; // 2 bytes, plus the 5 high-bits from usage counter
@SuppressWarnings( "unused" )
private static final int OFFSET_USAGE_COUNTER = 31; // 1 byte, but only the 3 low bits.
// The last word-line, with the file page id, swapper id, and usage counter, is called the page binding word.

// todo we can alternatively also make use of the lower 12 bits of the address field, because
// todo the addresses are page aligned, and we can assume them to be at least 4096 bytes in size.
Expand Down Expand Up @@ -178,7 +188,7 @@ private void clearMemorySimple( long baseAddress, long pageCount )
UnsafeUtil.putLong( address += Long.BYTES, initialLockWord ); // lock word
UnsafeUtil.putLong( address += Long.BYTES, 0 ); // pointer
UnsafeUtil.putLong( address += Long.BYTES, 0 ); // last tx id
UnsafeUtil.putLong( address += Long.BYTES, MAX_FILE_PAGE_ID << 24 );
UnsafeUtil.putLong( address += Long.BYTES, UNBOUND_PAGE_BINDING );
}
}

Expand Down Expand Up @@ -247,7 +257,7 @@ private long offAddress( long pageRef )
return pageRef + OFFSET_ADDRESS;
}

private long offFilePageId( long pageRef )
private long offPageBinding( long pageRef )
{
return pageRef + OFFSET_FILE_PAGE_ID;
}
Expand Down Expand Up @@ -338,7 +348,7 @@ public void initBuffer( long pageRef )

private byte getUsageCounter( long pageRef )
{
return (byte) (UnsafeUtil.getLongVolatile( offFilePageId( pageRef ) ) & 0x07);
return (byte) (UnsafeUtil.getLongVolatile( offPageBinding( pageRef ) ) & MASK_USAGE_COUNT);
}

/**
Expand All @@ -347,18 +357,18 @@ private byte getUsageCounter( long pageRef )
public void incrementUsage( long pageRef )
{
// This is intentionally left benignly racy for performance.
long address = offFilePageId( pageRef );
long address = offPageBinding( pageRef );
long v = UnsafeUtil.getLongVolatile( address );
long usage = v & 0x07;
if ( usage < 4 ) // avoid cache sloshing by not doing a write if counter is already maxed out
long usage = v & MASK_USAGE_COUNT;
if ( usage < MAX_USAGE_COUNT ) // avoid cache sloshing by not doing a write if counter is already maxed out
{
usage++;
// Use compareAndSwapLong to only actually store the updated count if nothing else changed
// in this word-line. The word-line is shared with the file page id, and the swapper id.
// Those fields are updated under guard of the exclusive lock, but we *might* race with
// that here, and in that case we would never want a usage counter update to clobber a page
// binding update.
UnsafeUtil.compareAndSwapLong( null, address, v, (v & 0xFFFFFFFF_FFFFFFF8L) + usage );
UnsafeUtil.compareAndSwapLong( null, address, v, (v & MASK_NOT_USAGE_COUNT) + usage );
}
}

Expand All @@ -368,21 +378,21 @@ public void incrementUsage( long pageRef )
public boolean decrementUsage( long pageRef )
{
// This is intentionally left benignly racy for performance.
long address = offFilePageId( pageRef );
long address = offPageBinding( pageRef );
long v = UnsafeUtil.getLongVolatile( address );
long usage = v & 0x07;
long usage = v & MASK_USAGE_COUNT;
if ( usage > 0 )
{
usage--;
// See `incrementUsage` about why we use `compareAndSwapLong`.
UnsafeUtil.compareAndSwapLong( null, address, v, (v & 0xFFFFFFFF_FFFFFFF8L) + usage );
UnsafeUtil.compareAndSwapLong( null, address, v, (v & MASK_NOT_USAGE_COUNT) + usage );
}
return usage == 0;
}

public long getFilePageId( long pageRef )
{
long filePageId = UnsafeUtil.getLong( offFilePageId( pageRef ) ) >>> 24;
long filePageId = UnsafeUtil.getLong( offPageBinding( pageRef ) ) >>> SHIFT_FILE_PAGE_ID;
return filePageId == MAX_FILE_PAGE_ID ? PageCursor.UNBOUND_PAGE_ID : filePageId;
}

Expand All @@ -393,9 +403,9 @@ private void setFilePageId( long pageRef, long filePageId )
throw new IllegalArgumentException(
format( "File page id: %s is bigger then max supported value %s.", filePageId, MAX_FILE_PAGE_ID ) );
}
long address = offFilePageId( pageRef );
long address = offPageBinding( pageRef );
long v = UnsafeUtil.getLong( address );
filePageId = (filePageId << 24) + (v & 0xFFFFFF);
filePageId = (filePageId << SHIFT_FILE_PAGE_ID) + (v & MASK_NOT_FILE_PAGE_ID);
UnsafeUtil.putLong( address, filePageId );
}

Expand All @@ -419,15 +429,15 @@ void setLastModifiedTxId( long pageRef, long modifierTxId )

public int getSwapperId( long pageRef )
{
long v = UnsafeUtil.getLong( offFilePageId( pageRef ) ) >>> 3;
return (int) (v & 0b1_11111_11111_11111_11111); // 21 bits.
long v = UnsafeUtil.getLong( offPageBinding( pageRef ) ) >>> SHIFT_SWAPPER_ID;
return (int) (v & MASK_SHIFTED_SWAPPER_ID); // 21 bits.
}

private void setSwapperId( long pageRef, int swapperId )
{
swapperId = swapperId << 3;
long address = offFilePageId( pageRef );
long v = UnsafeUtil.getLong( address ) & (~(0b1_11111_11111_11111_11111 << 3));
swapperId = swapperId << SHIFT_SWAPPER_ID;
long address = offPageBinding( pageRef );
long v = UnsafeUtil.getLong( address ) & MASK_NOT_SWAPPER_ID;
UnsafeUtil.putLong( address, v + swapperId );
}

Expand Down Expand Up @@ -551,10 +561,9 @@ private void flushModifiedPage( long pageRef, EvictionEvent evictionEvent, long
}
}

protected void clearBinding( long pageRef )
private void clearBinding( long pageRef )
{
setFilePageId( pageRef, PageCursor.UNBOUND_PAGE_ID );
setSwapperId( pageRef, (short) 0 );
UnsafeUtil.putLong( offPageBinding( pageRef ), UNBOUND_PAGE_BINDING );
}

public String toString( long pageRef )
Expand Down

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