Ptbm design details (1): buffer pool中内存页标识符的重新设计 & 多文件地址映射管理

// ptedit_header.h
typedef struct {
    size_t present : 1; // 
    size_t writeable : 1;
    size_t user_access : 1;
    size_t write_through : 1;
    size_t cache_disabled : 1;
    size_t accessed : 1;
    size_t dirty : 1;
    size_t size : 1;
    size_t global : 1;
    size_t ignored_2 : 3;
    size_t pfn : 28;
    size_t reserved_1 : 12;
    size_t ignored_1 : 11;
    size_t execution_disabled : 1;
} ptedit_pte_t;
// pte中预留了 12 + 11 + 3 = 26 bit

//==========================================================================
// buf_internals.h
/*
 * Buffer state is a single 32-bit variable where following data is combined.
 *
 * - 18 bits refcount
 * - 4 bits usage count
 * - 10 bits of flags
 *
 * Combining these values allows to perform some operations without locking
 * the buffer header, by modifying them together with a CAS loop.
 *
 * The definition of buffer state components is below.
 */
#define BUF_REFCOUNT_ONE 1
#define BUF_REFCOUNT_MASK ((1U << 18) - 1)
#define BUF_USAGECOUNT_MASK 0x003C0000U
#define BUF_USAGECOUNT_ONE (1U << 18)
#define BUF_USAGECOUNT_SHIFT 18
#define BUF_FLAG_MASK 0xFFC00000U

/* Get refcount and usagecount from buffer state */
#define BUF_STATE_GET_REFCOUNT(state) ((state) & BUF_REFCOUNT_MASK)
#define BUF_STATE_GET_USAGECOUNT(state) (((state) & BUF_USAGECOUNT_MASK) >> BUF_USAGECOUNT_SHIFT)
/*
 * Flags for buffer descriptors
 *
 * Note: BM_TAG_VALID essentially means that there is a buffer hashtable
 * entry associated with the buffer's tag.
 */
#define BM_LOCKED				(1U << 22)	/* buffer header is locked */
#define BM_DIRTY				(1U << 23)	/* data needs writing */
#define BM_VALID				(1U << 24)	/* data is valid */
#define BM_TAG_VALID			(1U << 25)	/* tag is assigned */
#define BM_IO_IN_PROGRESS		(1U << 26)	/* read or write in progress */
#define BM_IO_ERROR				(1U << 27)	/* previous I/O failed */
#define BM_JUST_DIRTIED			(1U << 28)	/* dirtied since write started */
#define BM_PIN_COUNT_WAITER		(1U << 29)	/* have waiter for sole pin */
#define BM_CHECKPOINT_NEEDED	(1U << 30)	/* must write for checkpoint */
#define BM_PERMANENT			(1U << 31)	/* permanent buffer (not unlogged,
											 * or init fork) */
typedef struct BufferDesc
{
	BufferTag	tag;			/* ID of page contained in buffer */
	int			buf_id;			/* buffer's index number (from 0) */

	/* state of the tag, containing flags, refcount and usagecount */
	pg_atomic_uint32 state;

	int			wait_backend_pgprocno;	/* backend of pin-count waiter */
	int			freeNext;		/* link in freelist chain */
	LWLock		content_lock;	/* to lock access to buffer contents */
} BufferDesc;

/*
 * The maximum allowed value of usage_count represents a tradeoff between
 * accuracy and speed of the clock-sweep buffer management algorithm.  A
 * large value (comparable to NBuffers) would approximate LRU semantics.
 * But it can take as many as BM_MAX_USAGE_COUNT+1 complete cycles of
 * clock sweeps to find a free buffer, so in practice we don't want the
 * value to be very large.
 */ 
#define BM_MAX_USAGE_COUNT	5

// /arch/x86/include/asm/pgtable_types.h

#define _PAGE_BIT_PRESENT	0	/* is present */
#define _PAGE_BIT_RW		1	/* writeable */
#define _PAGE_BIT_USER		2	/* userspace addressable */
#define _PAGE_BIT_PWT		3	/* page write through */
#define _PAGE_BIT_PCD		4	/* page cache disabled */
#define _PAGE_BIT_ACCESSED	5	/* was accessed (raised by CPU) */
#define _PAGE_BIT_DIRTY		6	/* was written to (raised by CPU) */
#define _PAGE_BIT_PSE		7	/* 4 MB (or 2MB) page */
#define _PAGE_BIT_PAT		7	/* on 4KB pages */
#define _PAGE_BIT_GLOBAL	8	/* Global TLB entry PPro+ */
#define _PAGE_BIT_SOFTW1	9	/* available for programmer */
#define _PAGE_BIT_SOFTW2	10	/* " */
#define _PAGE_BIT_SOFTW3	11	/* " */
#define _PAGE_BIT_PAT_LARGE	12	/* On 2MB or 1GB pages */
#define _PAGE_BIT_SOFTW4	58	/* available for programmer */
#define _PAGE_BIT_PKEY_BIT0	59	/* Protection Keys, bit 1/4 */
#define _PAGE_BIT_PKEY_BIT1	60	/* Protection Keys, bit 2/4 */
#define _PAGE_BIT_PKEY_BIT2	61	/* Protection Keys, bit 3/4 */
#define _PAGE_BIT_PKEY_BIT3	62	/* Protection Keys, bit 4/4 */
#define _PAGE_BIT_NX		63	/* No execute: only valid after cpuid check */

#define _PAGE_BIT_SPECIAL	_PAGE_BIT_SOFTW1
#define _PAGE_BIT_CPA_TEST	_PAGE_BIT_SOFTW1
#define _PAGE_BIT_UFFD_WP	_PAGE_BIT_SOFTW2 /* userfaultfd wrprotected */
#define _PAGE_BIT_SOFT_DIRTY	_PAGE_BIT_SOFTW3 /* software dirty tracking */
#define _PAGE_BIT_DEVMAP	_PAGE_BIT_SOFTW4