HP-UX Reference (11i v1 05/09) - 2 System Calls (vol 5)

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msync(2) msync(2)

HP-UX EXTENSIONS

NAME

msync - synchronize a mapped ﬁle

SYNOPSIS

int msync(caddr_t addr,size_t len, int flags);

DESCRIPTION

msync controls the caching operations of a mapped ﬁle region.

addr and len specify the region to be synchronized. If these are not the address and length of a region

created by a previous successful call to

mmap(), msync() returns an error. The behavior of msync()

upon a region created with the MAP_ANONYMOUS

or MAP_PRIVATE ﬂags is undeﬁned.

After a successful call to

msync() with

MS_SYNC speciﬁed, all previous modiﬁcations to the mapped

region are visible to processes using

read(). Previous modiﬁcations to the ﬁle using

write() may be

lost.

After a successful call to

msync() with only MS_INVALIDATE

speciﬁed, all previous modiﬁcations to

the ﬁle using

write() are visible to the mapped region. Previous direct modiﬁcations to the mapped

region may be lost.

Performance Considerations

The following performance considerations only apply when using the

MS_INVALIDATE option with

msync(). These performance constraints do not apply when either MS_ASYNC or MS_SYNC are

exclusively used with msync().

Direct read/write references to portions of a mapped memory region currently undergoing an

msync()

operation (with MS_INVALIDATE speciﬁed), may be blocked until all scheduled write operations are com-

pleted. This is especially true when performing an

msync() operation across a relatively large address

range that requires many individual write operations to be scheduled out to the underlying hardware. HP-

UX will schedule a separate write operation for each contiguous group of modiﬁed pages on disk. As more

write operations are queued out to the device, the overall suspension time of direct read/write references to

the same portions of the memory region will generally increase.

The suspension times of direct read/write references can be reduced by issuing

msync() requests over

smaller portions of the memory region, but issuing them more frequently than a corresponding larger syn-

chronization request. This will serve to more evenly distribute I/O activity across the mapped ﬁle, while

reducing the number of write operations per

msync().

ERRORS

[EINVAL] addr is not a multiple of the page size as returned by

sysconf(_SC_PAGE_SIZE)

[EINVAL] The address range speciﬁed by addr and len was not created by a successful call to

mmap().

AUTHOR

msync() was developed by HP, AT&T, and OSF.