linux-kernel - Re: [PATCH] mm/page_alloc: increase default min_free

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Message-Id: <20200220164033.8634c2c836c1558daebd81b9@linux-foundation.org>
Date:   Thu, 20 Feb 2020 16:40:33 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Joel Savitz <jsavitz@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Rafael Aquini <aquini@...hat.com>,
        linux-mm@...ck.org
Subject: Re: [PATCH] mm/page_alloc: increase default min_free_kbytes bound

On Thu, 20 Feb 2020 10:01:03 -0500 Joel Savitz <jsavitz@...hat.com> 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.

OK, better than nothing I guess.

> 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().
> 

Yup, these hardcoded numbers are lame.