linux-kernel - Re: [PATCH v3] mm: vmpressure: don't count proactive reclaim in vmpressure

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Date:   Fri, 1 Jul 2022 16:09:47 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Yosry Ahmed <yosryahmed@...gle.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Shakeel Butt <shakeelb@...gle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Matthew Wilcox <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Miaohe Lin <linmiaohe@...wei.com>, NeilBrown <neilb@...e.de>,
        Alistair Popple <apopple@...dia.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Peter Xu <peterx@...hat.com>, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v3] mm: vmpressure: don't count proactive reclaim in
 vmpressure

On Thu, 30 Jun 2022 08:30:44 +0000 Yosry Ahmed <yosryahmed@...gle.com> wrote:

> vmpressure is used in cgroup v1 to notify userspace of reclaim
> efficiency events, and is also used in both cgroup v1 and v2 as a signal
> for memory pressure for networking, see
> mem_cgroup_under_socket_pressure().
> 
> Proactive reclaim intends to probe memcgs for cold memory, without
> affecting their performance. Hence, reclaim caused by writing to
> memory.reclaim should not trigger vmpressure.
> 
> ...
>
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2319,6 +2319,7 @@ static unsigned long reclaim_high(struct mem_cgroup *memcg,
>  				  gfp_t gfp_mask)
>  {
>  	unsigned long nr_reclaimed = 0;
> +	unsigned int reclaim_options = MEMCG_RECLAIM_MAY_SWAP;
>  
>  	do {
>  		unsigned long pflags;
> @@ -2331,7 +2332,8 @@ static unsigned long reclaim_high(struct mem_cgroup *memcg,
>  
>  		psi_memstall_enter(&pflags);
>  		nr_reclaimed += try_to_free_mem_cgroup_pages(memcg, nr_pages,
> -							     gfp_mask, true);
> +							     gfp_mask,
> +							     reclaim_options);

It's a bit irksome to create all these unneeded local variables.  Why
not simply add the constant arg to the try_to_free_mem_cgroup_pages()
call?

>  		psi_memstall_leave(&pflags);
>  	} while ((memcg = parent_mem_cgroup(memcg)) &&
>  		 !mem_cgroup_is_root(memcg));
> @@ -2576,7 +2578,7 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
>  	struct page_counter *counter;
>  	unsigned long nr_reclaimed;
>  	bool passed_oom = false;
> -	bool may_swap = true;
> +	unsigned int reclaim_options = MEMCG_RECLAIM_MAY_SWAP;
>  	bool drained = false;
>  	unsigned long pflags;
>  
> @@ -2593,7 +2595,7 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
>  		mem_over_limit = mem_cgroup_from_counter(counter, memory);
>  	} else {
>  		mem_over_limit = mem_cgroup_from_counter(counter, memsw);
> -		may_swap = false;
> +		reclaim_options &= ~MEMCG_RECLAIM_MAY_SWAP;

	reclaim_options = 0

would be clearer?