Applications such as Just-In-Time (JIT) compilers, Checkpoint/Restore In Userspace (CRIU), and User Mode Linux (UML) need to know the highest virtual address, TASK_SIZE, to implement pointer tagging or make a first educated guess at where to find a large, unused region of memory. Unfortunately the currently available mechanisms for determining TASK_SIZE are either convoluted and potentially error-prone, such as making repeated munmap() calls and checking the return code, or make use of hard-coded assumptions that limit an application's portability across kernels with different Kconfig options and multiple architectures. Therefore, expose TASK_SIZE to userspace. While PAGE_SIZE is exposed to userspace via an auxiliary vector, that approach is not used for TASK_SIZE in case run-time alterations to the usable virtual address range are one day implemented, such as through an extension to prctl(PR_SET_MM) or a flag to clone. There is no prctl(PR_GET_MM). Instead such information is expected to come from /proc/<pid>/stat[m]. For the same extendability reason, use a per-pid proc entry rather than a system-wide entry like /proc/sys/vm/mmap_min_addr. Signed-off-by: Christopher Covington <cov@xxxxxxxxxxxxx> --- Documentation/filesystems/proc.txt | 1 + fs/proc/array.c | 5 +++++ 2 files changed, 6 insertions(+) diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt index 74329fd..b9c19cf 100644 --- a/Documentation/filesystems/proc.txt +++ b/Documentation/filesystems/proc.txt @@ -343,6 +343,7 @@ Table 1-4: Contents of the stat files (as of 2.6.30-rc7) env_start address above which program environment is placed env_end address below which program environment is placed exit_code the thread's exit_code in the form reported by the waitpid system call + end_mem address below which all regular program parts are placed (TASK_SIZE) .............................................................................. The /proc/PID/maps file containing the currently mapped memory regions and diff --git a/fs/proc/array.c b/fs/proc/array.c index 9a3ca9e..32b5002 100644 --- a/fs/proc/array.c +++ b/fs/proc/array.c @@ -561,6 +561,11 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns, else seq_puts(m, " 0"); + if (mm && permitted) + seq_put_decimal_ull(m, " ", mm->task_size); + else + seq_puts(m, " 0"); + seq_putc(m, '\n'); if (mm) mmput(mm); -- Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc. Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
