VMAllocator Class Reference

VMAllocator is an implementation of the CacheAllocator interface in terms of OS page allocation calls. More...

#include <VMAllocator.h>

Inheritance diagram for VMAllocator:

List of all members.

Public Member Functions
	VMAllocator (size_t cbAlloc, size_t nLocked=0)
	Constructs a new VMAllocator.
virtual	~VMAllocator ()
virtual void *	allocate (int *pErrorCode=NULL)
	Allocates a chunk of memory of size determined by the constructor.
virtual int	deallocate (void *pMem, int *pErrorCode=NULL)
	Deallocates a chunk of memory.
virtual int	setProtection (void *pMem, uint cb, bool readOnly, int *pErrorCode=NULL)
	Changes protection state for a contiguous range of virtual memory.
virtual size_t	getBytesAllocated () const
	Returns: number of bytes currently allocated
Private Attributes
size_t	cbAlloc
size_t	nAllocs
bool	bLockPages

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Detailed Description

VMAllocator is an implementation of the CacheAllocator interface in terms of OS page allocation calls.

Definition at line 35 of file VMAllocator.h.

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Constructor & Destructor Documentation

VMAllocator::VMAllocator	(	size_t	cbAlloc,
		size_t	nLocked = 0
	)			[explicit]

Constructs a new VMAllocator.

Parameters:

	cbAlloc	number of bytes per allocation; all calls to allocate must specify this same value
	nLocked	if nonzero, specifies that allocations should be locked in memory, and that no more than the specified number will be allocated at any one time

Definition at line 38 of file VMAllocator.cpp.

References bLockPages, cbAlloc, and nAllocs.

{
    cbAlloc = cbAllocInit;
    nAllocs = 0;
    if (nLocked) {
#ifdef RLIMIT_MEMLOCK
        struct rlimit rl;
        if (::getrlimit(RLIMIT_MEMLOCK,&rl)) {
            throw SysCallExcn("getrlimit failed");
        }
        if (rl.rlim_cur != RLIM_INFINITY) {
            // REVIEW:  what if other stuff in the same process needs
            // locked pages?
            rl.rlim_cur = nLocked*cbAlloc;
            rl.rlim_max = nLocked*cbAlloc;
            if (::setrlimit(RLIMIT_MEMLOCK,&rl)) {
                throw SysCallExcn("setrlimit failed");
            }
        }
#endif
        bLockPages = true;
    } else {
        bLockPages = false;
    }
}

VMAllocator::~VMAllocator

(

)

[virtual]

Definition at line 64 of file VMAllocator.cpp.

References getBytesAllocated().

{
    // This assertion indicates that not all allocated pages were deallocated.
    // In relation to LER-5976: in debug builds, each allocation is divided
    // into 3 sections (two guard pages surrounding the actual allocation).
    // The mprotect calls in allocate(int *) can fail in low memory situations
    // (the kernel may allocate private memory as it tracks a single mmap
    // region being split in three).  When this occurs, subsequent munmap calls
    // (even on different regions) in deallocate sometimes fail, leading to a
    // failure of this assertion.  This should not occur in release builds,
    // since no guard pages are allocated or protected. NOTE: On Ubuntu Edgy
    // Eft (2.6.17-12-generic SMP), the munmap calls in deallocate fails three
    // times, then inexplicably begin succeeding.  Retrying the failed calls
    // then succeeds.
    assert(!getBytesAllocated());
}

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Member Function Documentation

void * VMAllocator::allocate

(

int *

pErrorCode = NULL

)

[virtual]

Allocates a chunk of memory of size determined by the constructor.

Parameters:

pErrorCode

on error and if non-NULL, the int referenced is modified to contain the OS error code

Returns:

the allocated chunk; NULL if memory cannot be allocated (see pErrorCode for OS error code)

Implements CacheAllocator.

Definition at line 81 of file VMAllocator.cpp.

References bLockPages, cbAlloc, SysCallExcn::getCurrentErrorCode(), and nAllocs.

Referenced by RandomAccessFileDeviceTest::testAsyncIO().

{
#ifdef HAVE_MMAP

    uint cbActualAlloc = cbAlloc;
#ifndef NDEBUG
    // For a debug build, allocate "fence" regions before and after each
    // allocated buffer.  This helps to catch stray pointers around buffer
    // boundaries.  The fence size is one OS memory page, since that's
    // the minimum unit of protection, and also guarantees 512-byte
    // alignment for O_DIRECT file access.
    cbActualAlloc += 2*getpagesize();
#endif

    void *v = ::mmap(
        NULL,cbActualAlloc,
        PROT_READ | PROT_WRITE,MAP_PRIVATE | MAP_ANONYMOUS,-1,0);
    if (v == MAP_FAILED) {
        if (pErrorCode != NULL) {
            *pErrorCode = SysCallExcn::getCurrentErrorCode();
        }
        return NULL;
    }

#ifndef NDEBUG
    PBuffer p = static_cast<PBuffer>(v);
    memset(p, 0xFE, getpagesize());
    if (::mprotect(p, getpagesize(), PROT_NONE)) {
        if (pErrorCode != NULL) {
            *pErrorCode = SysCallExcn::getCurrentErrorCode();
        }
        ::munmap(v,cbAlloc);
        return NULL;
    }
    p += getpagesize();
    memset(p, 0xFF, cbAlloc);
    v = p;
    p += cbAlloc;
    memset(p, 0xFE, getpagesize());
    if (::mprotect(p, getpagesize(), PROT_NONE)) {
        if (pErrorCode != NULL) {
            *pErrorCode = SysCallExcn::getCurrentErrorCode();
        }
        ::munmap(v,cbAlloc);
        return NULL;
    }
#endif

    if (bLockPages) {
        if (::mlock(v,cbAlloc)) {
            if (pErrorCode != NULL) {
                *pErrorCode = SysCallExcn::getCurrentErrorCode();
            }
            ::munmap(v,cbAlloc);
            return NULL;
        }
    }
#else
    void *v = malloc(cbAlloc);
    if (v == NULL) {
        if (pErrorCode != NULL) {
            *pErrorCode = SysCallExcn::getCurrentErrorCode();
        }
        return NULL;
    }
#endif
    ++nAllocs;
    return v;
}

int VMAllocator::deallocate	(	void *	pMem,
		int *	pErrorCode = NULL
	)			[virtual]

Deallocates a chunk of memory.

Parameters:

	pMem	the allocated memory
	pErrorCode	on error and if non-NULL, the int referenced is modified to contain the OS error code

Returns:

0 on success; -1 if memory cannot be deallocated (see pErrorCode for OS error code)

Implements CacheAllocator.

Definition at line 151 of file VMAllocator.cpp.

References bLockPages, cbAlloc, free(), SysCallExcn::getCurrentErrorCode(), and nAllocs.

Referenced by RandomAccessFileDeviceTest::testAsyncIO().

{
#ifdef HAVE_MMAP
    if (bLockPages) {
        if (::munlock(p,cbAlloc)) {
            if (pErrorCode != NULL) {
                *pErrorCode = SysCallExcn::getCurrentErrorCode();
            }
            return -1;
        }
    }

    uint cbActualAlloc = cbAlloc;
#ifndef NDEBUG
    PBuffer p2 = static_cast<PBuffer>(p);
    p2 -= getpagesize();
    p = p2;
    cbActualAlloc += 2*getpagesize();
#endif
    if (::munmap((caddr_t)p,cbActualAlloc)) {
        if (pErrorCode != NULL) {
            *pErrorCode = SysCallExcn::getCurrentErrorCode();
        }
        return -1;
    }
#else
    free(p);
#endif
    --nAllocs;

    return 0;
}

int VMAllocator::setProtection	(	void *	pMem,
		uint	cb,
		bool	readOnly,
		int *	pErrorCode = NULL
	)			[virtual]

Changes protection state for a contiguous range of virtual memory.

Parameters:

	pMem	start of range
	cb	number of bytes in range
	readOnly	true for read-only; false for read-write (TODO jvs 7-Feb-2006: support no-access as well)
	pErrorCode	on error and if non-NULL, the int referenced is modified to contain the OS error code

Returns:

0 on success; -1 if an error occurs while manupulating memory protections (see pErrorCode for OS error code)

Implements CacheAllocator.

Definition at line 189 of file VMAllocator.cpp.

References SysCallExcn::getCurrentErrorCode().

{
    // FIXME jvs 7-Feb-2006:  use autoconf to get HAVE_MPROTECT instead
#ifdef HAVE_MMAP
    int prot = PROT_READ;
    if (!readOnly) {
        prot |= PROT_WRITE;
    }
    if (::mprotect(pMem, cb, prot)) {
        if (pErrorCode != NULL) {
            *pErrorCode = SysCallExcn::getCurrentErrorCode();
        }
        return -1;
    }
#endif

    return 0;
}

size_t VMAllocator::getBytesAllocated

(

)

const [virtual]

Returns:

number of bytes currently allocated

Implements CacheAllocator.

Definition at line 184 of file VMAllocator.cpp.

References cbAlloc, and nAllocs.

Referenced by ~VMAllocator().

{
    return nAllocs*cbAlloc;
}

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Member Data Documentation

size_t VMAllocator::cbAlloc [private]

Definition at line 38 of file VMAllocator.h.

Referenced by allocate(), deallocate(), getBytesAllocated(), and VMAllocator().

size_t VMAllocator::nAllocs [private]

Definition at line 39 of file VMAllocator.h.

Referenced by allocate(), deallocate(), getBytesAllocated(), and VMAllocator().

bool VMAllocator::bLockPages [private]

Definition at line 40 of file VMAllocator.h.

Referenced by allocate(), deallocate(), and VMAllocator().

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The documentation for this class was generated from the following files:

• /home/pub/open/dev/fennel/cache/VMAllocator.h
• /home/pub/open/dev/fennel/cache/VMAllocator.cpp

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