Re: [PATCH 1/6] mm/page_alloc: Delete vm.percpu_pagelist_fraction

[Dave Hansen]

On 5/21/21 3:28 AM, Mel Gorman wrote:
> The vm.percpu_pagelist_fraction is used to increase the batch and high
> limits for the per-cpu page allocator (PCP). The intent behind the sysctl
> is to reduce zone lock acquisition when allocating/freeing pages but it has
> a problem. While it can decrease contention, it can also increase latency
> on the allocation side due to unreasonably large batch sizes. This leads
> to games where an administrator adjusts percpu_pagelist_fraction on the
> fly to work around contention and allocation latency problems.
> 
> This series aims to alleviate the problems with zone lock contention while
> avoiding the allocation-side latency problems. For the purposes of review,
> it's easier to remove this sysctl now and reintroduce a similar sysctl
> later in the series that deals only with pcp->high.
> 
> Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>

I despise working with percpu_pagelist_fraction.  I usually just end up
poking random numbers into it and then checking what the fallout looks
like in /proc/zoneinfo is.

Good riddance.

Acked-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>