bufcache.c File Reference

#include <stdbool.h>
#include <stdint.h>
#include <string.h>
#include <sys/kassert.h>
#include <sys/kdebug.h>
#include <sys/kmem.h>
#include <sys/spinlock.h>
#include <sys/disk.h>
#include <sys/bufcache.h>
#include <errno.h>

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Macros
#define	CACHESIZE   (16*1024*1024)
#define	HASHTABLEENTRIES   128
#define	BLOCKSIZE   (16*1024)

Functions
static	TAILQ_HEAD (CacheHashTable, DEFINE_SLAB(BufCacheEntry)
static int	BufCacheLookup (Disk *disk, uint64_t diskOffset, BufCacheEntry **entry)
static int	BufCacheAlloc (Disk *disk, uint64_t diskOffset, BufCacheEntry **entry)
int	BufCache_Alloc (Disk *disk, uint64_t diskOffset, BufCacheEntry **entry)
void	BufCache_Release (BufCacheEntry *entry)
int	BufCache_Read (Disk *disk, uint64_t diskOffset, BufCacheEntry **entry)
int	BufCache_Write (BufCacheEntry *entry)
static void	Debug_BufCache (int argc, const char *argv[])
	REGISTER_DBGCMD (diskcache, "Display disk cache statistics", Debug_BufCache)

Variables
Spinlock	cacheLock
XMem *	diskBuf

Macro Definition Documentation

BLOCKSIZE

#define BLOCKSIZE   (16*1024)

CACHESIZE

#define CACHESIZE   (16*1024*1024)

HASHTABLEENTRIES

#define HASHTABLEENTRIES   128

Function Documentation

BufCache_Alloc()

int BufCache_Alloc	(	Disk *	disk,
		uint64_t	diskOffset,
		BufCacheEntry **	entry
	)

BufCache_Alloc –

Allocate a buffer cache entry to allow writing new data to disk.

Parameters

[in]	disk	Disk object
[in]	diskOffset	Block offset within the disk
[out]	entry	If successful, this contains the buffer cache entry.

Return values

0	if successful

Returns

Otherwise returns an error code.

Definition at line 178 of file bufcache.c.

{
    int status;
 
    Spinlock_Lock(&cacheLock);
 
    status = BufCacheLookup(disk, diskOffset, entry);
    if (*entry == NULL) {
        status = BufCacheAlloc(disk, diskOffset, entry);
    }
 
    cacheAlloc++;
 
    Spinlock_Unlock(&cacheLock);
 
    return status;
}

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BufCache_Read()

int BufCache_Read	(	Disk *	disk,
		uint64_t	diskOffset,
		BufCacheEntry **	entry
	)

BufCache_Read –

Read block from disk into the buffer cache.

Parameters

[in]	disk	Disk object
[in]	diskOffset	Block offset within the disk
[out]	entry	If successful, this contains the buffer cache entry.

Return values

0	if successful

Returns

Otherwise returns an error code.

Definition at line 229 of file bufcache.c.

{
    int status;
    void *buf;
    SGArray sga;
 
    Spinlock_Lock(&cacheLock);
    status = BufCacheLookup(disk, diskOffset, entry);
    if (*entry != NULL) {
        cacheHit++;
        Spinlock_Unlock(&cacheLock);
        return status;
    }
    cacheMiss++;
 
    status = BufCacheAlloc(disk, diskOffset, entry);
    if (status != 0) {
        Spinlock_Unlock(&cacheLock);
        return status;
    }
 
    buf = (*entry)->buffer;
    SGArray_Init(&sga);
    SGArray_Append(&sga, diskOffset, BLOCKSIZE);
 
    /*
     * XXX: Need to avoid holding cacheLock while reading from the disk, but 
     * need ensure other cores doesn't issue a read to the same block.
     */
    status = Disk_Read(disk, buf, &sga, NULL, NULL);
    Spinlock_Unlock(&cacheLock);
 
    return status;
}

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BufCache_Release()

void BufCache_Release

(

BufCacheEntry *

entry

)

BufCache_Release –

Release a buffer cache entry. If no other references are held the buffer cache entry is placed on the LRU list.

Parameters

[in]

entry

Buffer cache entry.

Definition at line 205 of file bufcache.c.

{
    Spinlock_Lock(&cacheLock);
 
    entry->refCount--;
    if (entry->refCount == 0) {
        TAILQ_INSERT_TAIL(&lruList, entry, lruEntry);
    }
 
    Spinlock_Unlock(&cacheLock);
}

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BufCache_Write()

int BufCache_Write

(

BufCacheEntry *

entry

)

BufCache_Write –

Write a buffer cache entry to disk.

Return values

0	if successful

Returns

Otherwise an error code is returned.

Definition at line 273 of file bufcache.c.

{
    void *buf = entry->buffer;
    SGArray sga;
 
    SGArray_Init(&sga);
    SGArray_Append(&sga, entry->diskOffset, BLOCKSIZE);
 
    return Disk_Write(entry->disk, buf, &sga, NULL, NULL);
}

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BufCacheAlloc()

static int BufCacheAlloc ( Disk *  disk, uint64_t  diskOffset, BufCacheEntry **  entry  )

static

BufCacheAlloc –

Allocates a buffer cache entry that can be used by BufCache_Alloc or BufCache_Read to allocate the underlying buffer..

Parameters

[in]	disk	Disk object
[in]	diskOffset	Block offset within the disk
[out]	entry	If successful, this contains the buffer cache entry.

Return values

0	if successful.

Returns

ENOMEM if there's no buffer cache entries free.

Definition at line 133 of file bufcache.c.

{
    struct CacheHashTable *table;
    BufCacheEntry *e;
 
    // Allocate from LRU list
    e = TAILQ_FIRST(&lruList);
    if (e == NULL) {
        kprintf("BufCache: No space left!\n");
        return ENOMEM;
    }
    TAILQ_REMOVE(&lruList, e, lruEntry);
 
    // Remove from hash table
    if (e->disk != NULL) {
        table = &hashTable[e->diskOffset % HASHTABLEENTRIES];
        TAILQ_REMOVE(table, e, htEntry);
    }
 
    // Initialize
    e->disk = disk;
    e->diskOffset = diskOffset;
    e->refCount = 1;
 
    // Reinsert into hash table
    table = &hashTable[diskOffset % HASHTABLEENTRIES];
    TAILQ_INSERT_HEAD(table, e, htEntry);
    *entry = e;
 
    return 0;
}

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BufCacheLookup()

static int BufCacheLookup ( Disk *  disk, uint64_t  diskOffset, BufCacheEntry **  entry  )

static

BufCacheLookup –

Looks up a buffer cache entry that can be used by BufCache_Alloc or BufCache_Read to allocate the underlying buffer.

Parameters

[in]	disk	Disk object
[in]	diskOffset	Block offset within the disk
[out]	entry	If successful, this contains the buffer cache entry.

Return values

0	if successful

Returns

ENOENT if not present.

Definition at line 97 of file bufcache.c.

{
    struct CacheHashTable *table;
    BufCacheEntry *e;
 
    // Check hash table
    table = &hashTable[diskOffset % HASHTABLEENTRIES];
    TAILQ_FOREACH(e, table, htEntry) {
        if (e->disk == disk && e->diskOffset == diskOffset) {
            e->refCount++;
            if (e->refCount == 1) {
                TAILQ_REMOVE(&lruList, e, lruEntry);
            }
            *entry = e;
            return 0;
        }
    }
 
    *entry = NULL;
    return ENOENT;
}

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Debug_BufCache()

static void Debug_BufCache ( int  argc, const char *  argv[]  )

static

Definition at line 285 of file bufcache.c.

{
    kprintf("Hits: %lld\n", cacheHit);
    kprintf("Misses: %lld\n", cacheMiss);
    kprintf("Allocations: %lld\n", cacheAlloc);
}

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REGISTER_DBGCMD()

REGISTER_DBGCMD	(	diskcache	,
		"Display disk cache statistics"	,
		Debug_BufCache
	)

TAILQ_HEAD()

static TAILQ_HEAD ( CacheHashTable  , DEFINE_SLAB(  BufCacheEntry  )

static

BufCache_Init –

Initialize the system buffer cache.

Definition at line 21 of file bufcache.c.

{
    int i;
 
    Spinlock_Init(&cacheLock, "BufCache Lock", SPINLOCK_TYPE_NORMAL);
 
    diskBuf = XMem_New();
    if (!diskBuf)
        Panic("BufCache: Cannot create XMem region\n");
 
    if (!XMem_Allocate(diskBuf, CACHESIZE))
        Panic("BufCache: Cannot back XMem region\n");
 
    TAILQ_INIT(&lruList);
 
    hashTable = PAlloc_AllocPage();
    if (!hashTable)
        Panic("BufCache: Cannot allocate hash table\n");
    for (i = 0; i < HASHTABLEENTRIES; i++) {
        TAILQ_INIT(&hashTable[i]);
    }
 
    Slab_Init(&cacheEntrySlab, "BufCacheEntry Slab", sizeof(BufCacheEntry), 16);
 
    // Initialize cache
    uintptr_t bufBase = XMem_GetBase(diskBuf);
    for (i = 0; i < CACHESIZE/BLOCKSIZE; i++) {
        BufCacheEntry *e = BufCacheEntry_Alloc();
        if (!e) {
            Panic("BufCache: Cannot allocate cache entry\n");
        }
 
        memset(e, 0, sizeof(*e));
        e->disk = NULL;
        e->buffer = (void *)(bufBase + BLOCKSIZE * i);
        TAILQ_INSERT_TAIL(&lruList, e, lruEntry);
    }
 
    cacheHit = 0;
    cacheMiss = 0;
    cacheAlloc = 0;
}

Variable Documentation

cacheLock

Spinlock cacheLock

Definition at line 18 of file bufcache.c.

diskBuf

XMem* diskBuf

Definition at line 19 of file bufcache.c.