linux-kernel - Re: [RFC][PATCH 11/13] mm/vmscan: Consider anonymous pages without swap

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Date:   Tue, 2 Feb 2021 14:35:00 -0800
From:   Yang Shi <shy828301@...il.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>, kbusch@...nel.org,
        "Verma, Vishal L" <vishal.l.verma@...el.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        David Rientjes <rientjes@...gle.com>,
        Huang Ying <ying.huang@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        David Hildenbrand <david@...hat.com>,
        Oscar Salvador <osalvador@...e.de>
Subject: Re: [RFC][PATCH 11/13] mm/vmscan: Consider anonymous pages without swap

On Tue, Feb 2, 2021 at 1:35 PM Dave Hansen <dave.hansen@...el.com> wrote:
>
> On 2/2/21 10:56 AM, Yang Shi wrote:
> >>
> >>         /* If we have no swap space, do not bother scanning anon pages. */
> >> -       if (!sc->may_swap || mem_cgroup_get_nr_swap_pages(memcg) <= 0) {
> >> +       if (!sc->may_swap || !can_reclaim_anon_pages(memcg, pgdat->node_id)) {
> > Just one minor thing about may_swap. It may be cleared by
> > nr_boost_reclaim. But demotion should be fine for boost_reclaim.
>
> In other words, this if() is here is to avoid generating suboptimal I/O
> during boost_reclaim.  But, since demotion doesn't generate any I/O, it
> *should* be fine for boost_reclaim.
>
> I agree with that in theory.  Although, I'm tempted to put it in the
> TODO list as something to look at in the future.  Do you think it's
> something that's immediately necessary?

No, I don't think so. We could tweak this later on.