madv.so.1

- madv library

Synopsis

/usr/lib/madv.so.1 

Description

The madv.so.1 shared object provides a means by which the VM advice can be selectively configured for a launched process (or processes) and its descendants. To enable madv.so.1, the following string needs to be present in the environment (see ld.so.1(1)) along with one or more MADV environment variables:

LD_PRELOAD=$LD_PRELOAD:madv.so.1

Environment Variables

If the madv.so.1 shared object is specified in the LD_PRELOAD list, the following environment variables are read by the madv shared object to determine to which created process(es) to apply the specified advice.

MADV=advice

MADV specifies the VM advice to use for all heap, shared memory, and mmap regions in the process address space. This advice is applied to all created processes.

Values for advice correspond to values in <sys/mman.h> used in madvise(3C) to specify memory access patterns:

normal random sequential access_lwp access_many access_many_pset access_default

MADVCFGFILE=config-file

config-file is a text file which contains one or more madv configuration entries of the form:

exec-name exec-args:advice-opts

Advice specified in config-file takes precedence over that specified by the MADV environment variable. When MADVCFGFILE is not set, advice is taken from file /etc/madv.conf if it exists.

exec-name specifies the name of an application or executable. The corresponding advice is set for newly created processes (see getexecname(3C)) that match the first exec-name found in the file.

exec-name can be a full pathname, a base name, or a pattern string. See File Name Generation in sh(1) for a discussion of pattern matching.

exec-args is an optionally specified pattern string to match against arguments. Advice is set only if exec-args is not specified or occurs within the arguments to exec-name.

advice-opts is a comma-separated list specifying the advice for various memory region(s):

madv=advice

Applies to all heap, shared memory, and mmap regions in the process address space.

heap=advice

The heap is defined to be the brk area (see brk(2)). Applies to the existing heap and for any additional heap memory allocated in the future.

shm=advice

ism=advice

dism=advice

Shared memory segments (see shmat(2)) attached using any flags, flag SHM_SHARE_MMU, or flag SHM_PAGEABLE respectively. Options ism and dism take precedence over option shm.

map=advice

mapshared=advice

mapprivate=advice

mapanon=advice

Mappings established through mmap(2) using any flags, flag MAP_SHARED, flag MAP_PRIVATE, or flag MAP_ANON, respectively. Options mapshared, mapprivate, and mapanon take precedence over option map. Option mapanon takes precedence over mapshared and mapprivate.

MADVERRFILE=pathname

By default, error messages are logged via syslog(3C) using level LOG_ERR and facility LOG_USER. If MADVERRFILE contains a valid pathname (such as /dev/stderr), error messages will be logged there instead.

Examples

Example 1 Applying Advice to All ISM Segments

The following configuration applies advice to all ISM segments for application /usr/bin/foo:

example$ LD_PRELOAD=$LD_PRELOAD:madv.so.1
example$ MADVCFGFILE=madvcfg
example$ export LD_PRELOAD MADVCFGFILE
example$ cat $MADVCFGFILE
    /usr/bin/foo:ism=access_lwp

Example 2 Setting Advice for All Applications with Exception

The following configuration sets advice for all applications with the exception of ls.

example$ LD_PRELOAD=$LD_PRELOAD:madv.so.1
example$ MADV=access_many
example$ MADVCFGFILE=madvcfg
example$ export LD_PRELOAD MADV MADVCFGFILE
example$ cat $MADVCFGFILE
    ls:

Example 3 Precedence Rules (continuation from Example 2)

Because MADVCFGFILE takes precedence over MADV, specifying '*' (pattern match all) for the exec-name of the last madv configuration entry would be equivalent to setting MADV. The following is equivalent to example 2:

example$ LD_PRELOAD=$LD_PRELOAD:madv.so.1
example$ MADVCFGFILE=madvcfg
example$ export LD_PRELOAD MADVCFGFILE
example$ cat $MADVCFGFILE
    ls:
    *:madv=access_many

Example 4 Applying Advice for Different Regions

The following configuration applies one type of advice for mmap regions and different advice for heap and shared memory regions for a select set of applications with exec names that begin with foo:

example$ LD_PRELOAD=$LD_PRELOAD:madv.so.1
example$ MADVCFGFILE=madvcfg
example$ export LD_PRELOAD MADVCFGFILE
example$ cat $MADVCFGFILE
    foo*:madv=access_many,heap=sequential,shm=access_lwp

Example 5 Applying Advice Selectively

The following configuration applies advice for the heap of applications beginning with ora that have ora1 as an argument:

example$ LD_PRELOAD=$LD_PRELOAD:madv.so.1
example$ MADVCFGFILE=madvcfg
example$ export LD_PRELOAD MADVCFGFILE
example$ cat $MADVCFGFILE
    ora* ora1:heap=access_many

Files

/etc/madv.conf

Configuration file

Attributes

See attributes(5) for descriptions of the following attributes:

See Also

cat(1), ld.so.1(1), proc(1), sh(1), brk(2), exec(2), fork(2), mmap(2), memcntl(2), shmat(2), getexecname(3C), madvise(3C), syslog(3C), proc(4), attributes(5)

Notes

The advice is inherited. A child process has the same advice as its parent. On exec() (see exec(2)), the advice is set back to the default system advice unless different advice has been configured via the madv shared object.

Advice is only applied to mmap regions explicitly created by the user program. Those regions established by the run-time linker or by system libraries making direct system calls (for example, libthread allocations for thread stacks) are not affected.