On Tue, Apr 28, 2020 at 3:11 PM Nitin Gupta <nigupta@nvidia.com> wrote:

> For some applications, we need to allocate almost all memory as
> hugepages. However, on a running system, higher-order allocations can
> fail if the memory is fragmented. Linux kernel currently does on-demand
> compaction as we request more hugepages, but this style of compaction
> incurs very high latency. Experiments with one-time full memory
> compaction (followed by hugepage allocations) show that kernel is able
> to restore a highly fragmented memory state to a fairly compacted memory
> state within <1 sec for a 32G system. Such data suggests that a more
> proactive compaction can help us allocate a large fraction of memory as
> hugepages keeping allocation latencies low.
>
> For a more proactive compaction, the approach taken here is to define
> a new tunable called 'proactiveness' which dictates bounds for external
> fragmentation wrt HUGETLB_PAGE_ORDER order which kcompactd tries to
> maintain.
>
> The tunable is exposed through sysfs:
>   /sys/kernel/mm/compaction/proactiveness
>
>
> <snip>


Ping.

Any comments/feedback?

-Nitin