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SubjectRe: [PATCH v4 3/4] mm/page_reporting: Allow driver to specify reporting order
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On 6/25/21 3:48 PM, Michael S. Tsirkin wrote:
> On Fri, Jun 25, 2021 at 09:47:09AM +0800, Gavin Shan wrote:
>> The page reporting order (threshold) is sticky to @pageblock_order
>> by default. The page reporting can never be triggered because the
>> freeing page can't come up with a free area like that huge. The
>> situation becomes worse when the system memory becomes heavily
>> fragmented.
>>
>> For example, the following configurations are used on ARM64 when 64KB
>> base page size is enabled. In this specific case, the page reporting
>> won't be triggered until the freeing page comes up with a 512MB free
>> area. That's hard to be met, especially when the system memory becomes
>> heavily fragmented.
>>
>> PAGE_SIZE: 64KB
>> HPAGE_SIZE: 512MB
>> pageblock_order: 13 (512MB)
>> MAX_ORDER: 14
>>
>> This allows the drivers to specify the page reporting order when the
>> page reporting device is registered. It falls back to @pageblock_order
>> if it's not specified by the driver. The existing users (hv_balloon
>> and virtio_balloon) don't specify it and @pageblock_order is still
>> taken as their page reporting order. So this shouldn't introduce any
>> functional changes.
>>
>> Signed-off-by: Gavin Shan <gshan@redhat.com>
>> Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
>> ---
>> include/linux/page_reporting.h | 3 +++
>> mm/page_reporting.c | 6 ++++++
>> 2 files changed, 9 insertions(+)
>>
>> diff --git a/include/linux/page_reporting.h b/include/linux/page_reporting.h
>> index 3b99e0ec24f2..fe648dfa3a7c 100644
>> --- a/include/linux/page_reporting.h
>> +++ b/include/linux/page_reporting.h
>> @@ -18,6 +18,9 @@ struct page_reporting_dev_info {
>>
>> /* Current state of page reporting */
>> atomic_t state;
>> +
>> + /* Minimal order of page reporting */
>> + unsigned int order;
>> };
>>
>> /* Tear-down and bring-up for page reporting devices */
>> diff --git a/mm/page_reporting.c b/mm/page_reporting.c
>> index 34bf4d26c2c4..382958eef8a9 100644
>> --- a/mm/page_reporting.c
>> +++ b/mm/page_reporting.c
>> @@ -329,6 +329,12 @@ int page_reporting_register(struct page_reporting_dev_info *prdev)
>> goto err_out;
>> }
>>
>> + /*
>> + * Update the page reporting order if it's specified by driver.
>> + * Otherwise, it falls back to @pageblock_order.
>> + */
>> + page_reporting_order = prdev->order ? : pageblock_order;
>> +
>
> Hmm. So on ARM achitectures with 64K pages, the command line parameter
> is silently ignored?
>
> Isn't this a problem?
>

It's fine as the command line parameter is used as debugging purpose.
Besides, it can be changed by writing to the following file:

/sys/module/page_reporting/parameters/page_reporting_order


>> /* initialize state and work structures */
>> atomic_set(&prdev->state, PAGE_REPORTING_IDLE);
>> INIT_DELAYED_WORK(&prdev->work, &page_reporting_process);
>> --
>> 2.23.0

Thanks,
Gavin

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