Re: [PATCH 0/1] mm, compaction: correct the bounds of __fragmentation_index()

Robert Harris
2018-02-19T11:40:39Z

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> On 19 Feb 2018, at 08:24, Michal Hocko <mhocko@kernel.org> wrote:
>
> On Sun 18-02-18 16:47:54, robert.m.harris@oracle.com <mailto:robert.m.harris@oracle.com> wrote:
>> From: "Robert M. Harris" <robert.m.harris@oracle.com>
>>
>> __fragmentation_index() calculates a value used to determine whether
>> compaction should be favoured over page reclaim in the event of
>> allocation failure. The function purports to return a value between 0
>> and 1000, representing units of 1/1000. Barring the case of a
>> pathological shortfall of memory, the lower bound is instead 500. This
>> is significant because it is the default value of
>> sysctl_extfrag_threshold, i.e. the value below which compaction should
>> be avoided in favour of page reclaim for costly pages.
>>
>> Here's an illustration using a zone that I fragmented with selective
>> calls to __alloc_pages() and __free_pages --- the fragmentation for
>> order-1 could not be minimised further yet is reported as 0.5:
>
> Cover letter for a single patch is usually an overkill. Why is this
> information not valuable in the patch description directly?

This is my first patch and I’m not familiar with all the conventions.
I’ll incorporate those details in the next version of the commit message.

Robert Harris

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