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Message-ID: <2e22fe80-2280-4003-923d-8749fe85b81a@redhat.com>
Date:   Tue, 12 Dec 2023 19:07:52 +0100
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User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH v3 2/4] mm/ksm: add sysfs knobs for advisor
Content-Language: en-US
To:     Stefan Roesch <shr@devkernel.io>, kernel-team@fb.com
Cc:     Andrew Morton <akpm@linux-foundation.org>, hannes@cmpxchg.org,
        riel@surriel.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org
References: <20231204234906.1237478-1-shr@devkernel.io>
 <20231204234906.1237478-3-shr@devkernel.io>
 <ebea3b6f-efc0-4d98-bf4d-3e2b867fa886@redhat.com>
 <a0c4f60b-77de-44c1-b348-2fbf12494630@app.fastmail.com>
From:   David Hildenbrand <david@redhat.com>
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Organization: Red Hat
In-Reply-To: <a0c4f60b-77de-44c1-b348-2fbf12494630@app.fastmail.com>
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On 12.12.23 19:02, Stefan Roesch wrote:
> 
> 
> On Tue, Dec 12, 2023, at 5:45 AM, David Hildenbrand wrote:
>> On 05.12.23 00:49, Stefan Roesch wrote:
>>> This adds four new knobs for the KSM advisor to influence its behaviour.
>>>
>>> The knobs are:
>>> - advisor_mode:
>>>       none:      no advisor (default)
>>>       scan-time: scan time advisor
>>> - advisor_max_cpu: 70 (default, cpu usage percent)
>>> - advisor_min_pages: 500 (default)
>>> - advisor_max_pages: 30000 (default)
>>> - advisor_target_scan_time: 200 (default in seconds)
>>>
>>> The new values will take effect on the next scan round.
>>>
>>> Signed-off-by: Stefan Roesch <shr@devkernel.io>
>>> ---
>>>    mm/ksm.c | 127 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>>    1 file changed, 127 insertions(+)
>>>
>>> diff --git a/mm/ksm.c b/mm/ksm.c
>>> index b27010fa2e946..18b7185bbc65b 100644
>>> --- a/mm/ksm.c
>>> +++ b/mm/ksm.c
>>> @@ -3735,6 +3735,128 @@ static ssize_t smart_scan_store(struct kobject *kobj,
>>>    }
>>>    KSM_ATTR(smart_scan);
>>>    
>>> +static ssize_t advisor_mode_show(struct kobject *kobj,
>>> +				 struct kobj_attribute *attr, char *buf)
>>> +{
>>> +	const char *output;
>>> +
>>> +	if (ksm_advisor == KSM_ADVISOR_NONE)
>>> +		output = "[none] scan-time";
>>> +	else if (ksm_advisor == KSM_ADVISOR_SCAN_TIME)
>>> +		output = "none [scan-time]";
>>> +
>>> +	return sysfs_emit(buf, "%s\n", output);
>>> +}
>>> +
>>> +static ssize_t advisor_mode_store(struct kobject *kobj,
>>> +				  struct kobj_attribute *attr, const char *buf,
>>> +				  size_t count)
>>> +{
>>> +	if (sysfs_streq("scan-time", buf))
>>> +		ksm_advisor = KSM_ADVISOR_SCAN_TIME;
>>> +	else if (sysfs_streq("none", buf))
>>> +		ksm_advisor = KSM_ADVISOR_NONE;
>>> +	else
>>> +		return -EINVAL;
>>> +
>>> +	/* Set advisor default values */
>>> +	init_advisor();
>>
>> Is the "init_advisor()" really required?
>>
> 
> The init_advisor is required for the following scenario:
> - advisor is used
> - advisor is turned off
> - pages_to_scan is used and run for some time
> - advisor is turned on again
>     ==> Advisor would start with two high values for the first calculation

Can't set_advisor_defaults() handle that?

-- 
Cheers,

David / dhildenb