linux-kernel - Re: [PATCH] mm, memcg: reclaim more aggressively before high allocator throttling

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Date:   Thu, 28 May 2020 20:48:31 +0100
From:   Chris Down <chris@...isdown.name>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Tejun Heo <tj@...nel.org>, Michal Hocko <mhocko@...nel.org>,
        Linux MM <linux-mm@...ck.org>,
        Cgroups <cgroups@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH] mm, memcg: reclaim more aggressively before high
 allocator throttling

Shakeel Butt writes:
>What was the initial reason to have different behavior in the first place?

This differing behaviour is simply a mistake, it was never intended to be this 
deviate from what happens elsewhere. To that extent this patch is as much a bug 
fix as it is an improvement.

>>  static void high_work_func(struct work_struct *work)
>> @@ -2378,16 +2384,20 @@ void mem_cgroup_handle_over_high(void)
>>  {
>>         unsigned long penalty_jiffies;
>>         unsigned long pflags;
>> +       unsigned long nr_reclaimed;
>>         unsigned int nr_pages = current->memcg_nr_pages_over_high;
>
>Is there any benefit to keep current->memcg_nr_pages_over_high after
>this change? Why not just use SWAP_CLUSTER_MAX?

I don't feel strongly either way, but current->memcg_nr_pages_over_high can be 
very large for large allocations.

That said, maybe we should just reclaim `max(SWAP_CLUSTER_MAX, current - high)` 
for each loop? I agree that with this design it looks like perhaps we don't 
need it any more.

Johannes, what do you think?