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SubjectRe: [PATCH] mm/page_alloc: increase default min_free_kbytes bound
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On 2/21/20 2:53 AM, John Hubbard wrote:
> On 2/20/20 7:01 AM, Joel Savitz wrote:
>>
>> Currently, the vm.min_free_kbytes sysctl value is capped at a hardcoded
>> 64M in init_per_zone_wmark_min (unless it is overridden by khugepaged
>> initialization).
>>
>> This value has not been modified since 2005, and enterprise-grade
>> systems now frequently have hundreds of GB of RAM and multiple 10, 40,
>> or even 100 GB NICs. We have seen page allocation failures on heavily
>> loaded systems related to NIC drivers. These issues were resolved by an
>> increase to vm.min_free_kbytes.
>>
>> This patch increases the hardcoded value by a factor of 4 as a temporary
>> solution.
>>
>> Further work to make the calculation of vm.min_free_kbytes more
>> consistent throughout the kernel would be desirable.
>>
>> As an example of the inconsistency of the current method, this value is
>> recalculated by init_per_zone_wmark_min() in the case of memory hotplug
>> which will override the value set by set_recommended_min_free_kbytes()
>> called during khugepaged initialization even if khugepaged remains
>> enabled, however an on/off toggle of khugepaged will then recalculate
>> and set the value via set_recommended_min_free_kbytes().
>>
>> Signed-off-by: Joel Savitz <jsavitz@redhat.com>
>> ---
>> mm/page_alloc.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 3c4eb750a199..32cbfb13e958 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -7867,8 +7867,8 @@ int __meminit init_per_zone_wmark_min(void)
>> min_free_kbytes = new_min_free_kbytes;
>> if (min_free_kbytes < 128)
>> min_free_kbytes = 128;
>> - if (min_free_kbytes > 65536)
>> - min_free_kbytes = 65536;
>> + if (min_free_kbytes > 262144)
>> + min_free_kbytes = 262144;
>
>
> Would it be any better to at least use symbols, instead of numbers, in the
> routine? Like this:

+1

Thanks

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