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SubjectRe: [v3 1/2] mm: khugepaged: recalculate min_free_kbytes after memory hotplug as expected by khugepaged
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On 9/25/2020 12:42 AM, Michal Hocko wrote:
> On Wed 16-09-20 18:21:48, Vijay Balakrishna wrote:
>> When memory is hotplug added or removed the min_free_kbytes must be
>> recalculated based on what is expected by khugepaged. Currently
>> after hotplug, min_free_kbytes will be set to a lower default and higher
>> default set when THP enabled is lost. This change restores min_free_kbytes
>> as expected for THP consumers.
>>
>> Fixes: f000565adb77 ("thp: set recommended min free kbytes")
>>
>> Signed-off-by: Vijay Balakrishna <vijayb@linux.microsoft.com>
>> Cc: stable@vger.kernel.org
>> Reviewed-by: Pavel Tatashin <pasha.tatashin@soleen.com>
>
> I am ok with this patch. I am not sure this is worth backporting to
> stable trees becasuse this is not a functional bug. Surprising behavior,
> yes, but not much more than that.
>
> Acked-by: Michal Hocko <mhocko@suse.com>

Thanks Michal.

>
> One minor comment below
> [...]
>> @@ -857,6 +858,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
>> zone_pcp_update(zone);
>>
>> init_per_zone_wmark_min();
>> + khugepaged_min_free_kbytes_update();
>>
>> kswapd_run(nid);
>> kcompactd_run(nid);
>> @@ -1600,6 +1602,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
>> pgdat_resize_unlock(zone->zone_pgdat, &flags);
>>
>> init_per_zone_wmark_min();
>> + khugepaged_min_free_kbytes_update();
>>
>> if (!populated_zone(zone)) {
>> zone_pcp_reset(zone);
>
> Can we move khugepaged_min_free_kbytes_update into
> init_per_zone_wmark_min? If it stays external we might hit the same
> problem when somebody else needs to modify min_free_kbytes. Early init
> call will be likely too early for khugepaged but that shouldn't matter
> AFAICS because it will call khugepaged_min_free_kbytes_update on its
> own.

Sure, let me take a look and post v4 next week.

Thanks,
Vijay

>

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