Re: [RFC 1/4] mm: Per process reclaim

[Michael Kerrisk]

Hello Minchan,

On Mon, Mar 25, 2013 at 7:21 AM, Minchan Kim <minchan@xxxxxxxxxx> wrote:
> These day, there are many platforms avaiable in the embedded market
> and they are smarter than kernel which has very limited information
> about working set so they want to involve memory management more heavily
> like android's lowmemory killer and ashmem or recent many lowmemory
> notifier(there was several trial for various company NOKIA, SAMSUNG,
> Linaro, Google ChromeOS, Redhat).
>
> One of the simple imagine scenario about userspace's intelligence is that
> platform can manage tasks as forground and backgroud so it would be
> better to reclaim background's task pages for end-user's *responsibility*
> although it has frequent referenced pages.
>
> This patch adds new knob "reclaim under proc/<pid>/" so task manager
> can reclaim any target process anytime, anywhere. It could give another
> method to platform for using memory efficiently.
>
> It can avoid process killing for getting free memory, which was really
> terrible experience because I lost my best score of game I had ever
> after I switch the phone call while I enjoyed the game.
>
> Writing 1 to /proc/pid/reclaim reclaims only file pages.
> Writing 2 to /proc/pid/reclaim reclaims only anonymous pages.
> Writing 3 to /proc/pid/reclaim reclaims all pages from target process.
>
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> ---
>  fs/proc/base.c       |   3 ++
>  fs/proc/internal.h   |   1 +
>  fs/proc/task_mmu.c   | 115 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/rmap.h |   4 ++
>  mm/Kconfig           |  13 ++++++
>  mm/internal.h        |   7 +---
>  mm/vmscan.c          |  59 ++++++++++++++++++++++++++
>  7 files changed, 196 insertions(+), 6 deletions(-)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 9b43ff77..ed83e85 100644

[...]

> +#define RECLAIM_FILE (1 << 0)
> +#define RECLAIM_ANON (1 << 1)
> +#define RECLAIM_ALL (RECLAIM_FILE | RECLAIM_ANON)
> +
> +static ssize_t reclaim_write(struct file *file, const char __user *buf,
> +                               size_t count, loff_t *ppos)
> +{
> +       struct task_struct *task;
> +       char buffer[PROC_NUMBUF];
> +       struct mm_struct *mm;
> +       struct vm_area_struct *vma;
> +       int type;
> +       int rv;
> +
> +       memset(buffer, 0, sizeof(buffer));
> +       if (count > sizeof(buffer) - 1)
> +               count = sizeof(buffer) - 1;
> +       if (copy_from_user(buffer, buf, count))
> +               return -EFAULT;
> +       rv = kstrtoint(strstrip(buffer), 10, &type);
> +       if (rv < 0)
> +               return rv
> +       if (type < RECLAIM_ALL || type > RECLAIM_FILE)
> +               return -EINVAL;> +       task = get_proc_task(file->f_path.dentry->d_inode);

The check here is the wrong way round. Should be

       if (type < RECLAIM_FILE || type > RECLAIM_ALL)

Thanks,

Michael
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