linux-kernel - Re: [PATCH RFC v2 3/4] mm/ksm: introduce force

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Date:   Tue, 14 May 2019 14:22:49 +0100
From:   Aaron Tomlin <atomlin@...hat.com>
To:     Oleksandr Natalenko <oleksandr@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Kirill Tkhai <ktkhai@...tuozzo.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>,
        Matthew Wilcox <willy@...radead.org>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Timofey Titovets <nefelim4ag@...il.com>,
        Grzegorz Halat <ghalat@...hat.com>, linux-mm@...ck.org
Subject: Re: [PATCH RFC v2 3/4] mm/ksm: introduce force_madvise knob

On Tue 2019-05-14 15:16 +0200, Oleksandr Natalenko wrote:
> Present a new sysfs knob to mark task's anonymous memory as mergeable.
> 
> To force merging task's VMAs, its PID is echoed in a write-only file:
> 
>    # echo PID > /sys/kernel/mm/ksm/force_madvise
> 
> Force unmerging is done similarly, but with "minus" sign:
> 
>    # echo -PID > /sys/kernel/mm/ksm/force_madvise
> 
> "0" or "-0" can be used to control the current task.
> 
> To achieve this, previously introduced ksm_enter()/ksm_leave() helpers
> are used in the "store" handler.
> 
> Signed-off-by: Oleksandr Natalenko <oleksandr@...hat.com>
> ---
>  mm/ksm.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 68 insertions(+)
> 
> diff --git a/mm/ksm.c b/mm/ksm.c
> index e9f3901168bb..22c59fb03d3a 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -2879,10 +2879,77 @@ static void wait_while_offlining(void)
>  
>  #define KSM_ATTR_RO(_name) \
>  	static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
> +#define KSM_ATTR_WO(_name) \
> +	static struct kobj_attribute _name##_attr = __ATTR_WO(_name)
>  #define KSM_ATTR(_name) \
>  	static struct kobj_attribute _name##_attr = \
>  		__ATTR(_name, 0644, _name##_show, _name##_store)
>  
> +static ssize_t force_madvise_store(struct kobject *kobj,
> +				     struct kobj_attribute *attr,
> +				     const char *buf, size_t count)
> +{
> +	int err;
> +	pid_t pid;
> +	bool merge = true;
> +	struct task_struct *tsk;
> +	struct mm_struct *mm;
> +	struct vm_area_struct *vma;
> +
> +	err = kstrtoint(buf, 10, &pid);
> +	if (err)
> +		return -EINVAL;
> +
> +	if (pid < 0) {
> +		pid = abs(pid);
> +		merge = false;
> +	}
> +
> +	if (!pid && *buf == '-')
> +		merge = false;
> +
> +	rcu_read_lock();
> +	if (pid) {
> +		tsk = find_task_by_vpid(pid);
> +		if (!tsk) {
> +			err = -ESRCH;
> +			rcu_read_unlock();
> +			goto out;
> +		}
> +	} else {
> +		tsk = current;
> +	}
> +
> +	tsk = tsk->group_leader;
> +
> +	get_task_struct(tsk);
> +	rcu_read_unlock();
> +
> +	mm = get_task_mm(tsk);
> +	if (!mm) {
> +		err = -EINVAL;
> +		goto out_put_task_struct;
> +	}
> +	down_write(&mm->mmap_sem);
> +	vma = mm->mmap;
> +	while (vma) {
> +		if (merge)
> +			ksm_enter(vma->vm_mm, vma, &vma->vm_flags);
> +		else
> +			ksm_leave(vma, vma->vm_start, vma->vm_end, &vma->vm_flags);
> +		vma = vma->vm_next;
> +	}
> +	up_write(&mm->mmap_sem);
> +	mmput(mm);
> +
> +out_put_task_struct:
> +	put_task_struct(tsk);
> +
> +out:
> +	return err ? err : count;
> +}
> +KSM_ATTR_WO(force_madvise);
> +
>  static ssize_t sleep_millisecs_show(struct kobject *kobj,
>  				    struct kobj_attribute *attr, char *buf)
>  {
> @@ -3185,6 +3252,7 @@ static ssize_t full_scans_show(struct kobject *kobj,
>  KSM_ATTR_RO(full_scans);
>  
>  static struct attribute *ksm_attrs[] = {
> +	&force_madvise_attr.attr,
>  	&sleep_millisecs_attr.attr,
>  	&pages_to_scan_attr.attr,
>  	&run_attr.attr,

Looks fine to me.

Reviewed-by: Aaron Tomlin <atomlin@...hat.com>

-- 
Aaron Tomlin