Re: [PATCH v3] fs/proc: add VmTaskSize field to /proc/$$/status

[Rafael Aquini]

On Mon, May 06, 2019 at 11:53:43AM -0400, Joel Savitz wrote:
> There is currently no easy and architecture-independent way to find the
> lowest unusable virtual address available to a process without
> brute-force calculation. This patch allows a user to easily retrieve
> this value via /proc/<pid>/status.
> 
> Using this patch, any program that previously needed to waste cpu cycles
> recalculating a non-sensitive process-dependent value already known to
> the kernel can now be optimized to use this mechanism.
> 
> Signed-off-by: Joel Savitz <jsavitz@xxxxxxxxxx>
> ---
>  Documentation/filesystems/proc.txt | 2 ++
>  fs/proc/task_mmu.c                 | 2 ++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
> index 66cad5c86171..1c6a912e3975 100644
> --- a/Documentation/filesystems/proc.txt
> +++ b/Documentation/filesystems/proc.txt
> @@ -187,6 +187,7 @@ read the file /proc/PID/status:
>    VmLib:      1412 kB
>    VmPTE:        20 kb
>    VmSwap:        0 kB
> +  VmTaskSize:	137438953468 kB
>    HugetlbPages:          0 kB
>    CoreDumping:    0
>    THP_enabled:	  1
> @@ -263,6 +264,7 @@ Table 1-2: Contents of the status files (as of 4.19)
>   VmPTE                       size of page table entries
>   VmSwap                      amount of swap used by anonymous private data
>                               (shmem swap usage is not included)
> + VmTaskSize                  lowest unusable address in process virtual memory

Can we change this help text to "size of process' virtual address space memory" ?

>   HugetlbPages                size of hugetlb memory portions
>   CoreDumping                 process's memory is currently being dumped
>                               (killing the process may lead to a corrupted core)
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 95ca1fe7283c..0af7081f7b19 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -74,6 +74,8 @@ void task_mem(struct seq_file *m, struct mm_struct *mm)
>  	seq_put_decimal_ull_width(m,
>  		    " kB\nVmPTE:\t", mm_pgtables_bytes(mm) >> 10, 8);
>  	SEQ_PUT_DEC(" kB\nVmSwap:\t", swap);
> +	seq_put_decimal_ull_width(m,
> +		    " kB\nVmTaskSize:\t", mm->task_size >> 10, 8);
>  	seq_puts(m, " kB\n");
>  	hugetlb_report_usage(m, mm);
>  }
> -- 
> 2.18.1
> 
Acked-by: Rafael Aquini <aquini@xxxxxxxxxx>