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    Subject[PATCH 4/4] coredump: documentation for proc entry
    This patch adds the documentation for

    Signed-off-by: Hidehiro Kawai <>
    Documentation/filesystems/proc.txt | 38 +++++++++++++++++++++++++++
    1 files changed, 38 insertions(+)

    Index: linux-2.6.20-mm1/Documentation/filesystems/proc.txt
    --- linux-2.6.20-mm1.orig/Documentation/filesystems/proc.txt
    +++ linux-2.6.20-mm1/Documentation/filesystems/proc.txt
    @@ -41,6 +41,7 @@ Table of Contents
    2.11 /proc/sys/fs/mqueue - POSIX message queues filesystem
    2.12 /proc/<pid>/oom_adj - Adjust the oom-killer score
    2.13 /proc/<pid>/oom_score - Display current oom-killer score
    + 2.14 /proc/<pid>/coredump_omit_anonymous_shared - Core dump coordinator

    @@ -1982,6 +1983,43 @@ This file can be used to check the curre
    any given <pid>. Use it together with /proc/<pid>/oom_adj to tune which
    process should be killed in an out-of-memory situation.

    +2.14 /proc/<pid>/coredump_omit_anonymous_shared - Core dump coordinator
    +When a process is dumped, all anonymous memory is written to a core file as
    +long as the size of the core file isn't limited. But sometimes we don't want
    +to dump some memory segments, for example, huge shared memory.
    +The /proc/<pid>/coredump_omit_anonymous_shared is a flag which enables you to
    +omit anonymous shared memory segments from a core file when it is generated.
    +When the <pid> process is dumped, the core dump routine decides whether a
    +given memory segment should be dumped into a core file or not based on the
    +type of the memory segment and the flag.
    +If you have written a non-zero value to this proc file, anonymous shared
    +memory segments are not dumped. There are three types of anonymous shared
    + - IPC shared memory
    + - the memory segments created by mmap(2) with MAP_ANONYMOUS and MAP_SHARED
    + flags
    + - the memory segments created by mmap(2) with MAP_SHARED flag, and the
    + mapped file has already been unlinked
    +Because current core dump routine doesn't distinguish these segments, you can
    +only choose either dumping all anonymous shared memory segments or not.
    +If you don't want to dump all shared memory segments attached to pid 1234,
    +write 0 to the process's proc file.
    + $ echo 1 > /proc/1234/coredump_omit_anonymous_shared
    +When a new process is created, the process inherits the flag status from its
    +parent. It is useful to set the flag before the program runs.
    +For example:
    + $ echo 1 > /proc/self/coredump_omit_anonymous_shared
    + $ ./some_program

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