linux-kernel - Re: [RFC][PATCH 7/9] mm/vmscan: Consider anonymous pages without swap

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Date:   Thu, 29 Oct 2020 12:30:51 -0700
From:   Yang Shi <shy828301@...il.com>
To:     osalvador <osalvador@...e.de>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        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>
Subject: Re: [RFC][PATCH 7/9] mm/vmscan: Consider anonymous pages without swap

On Thu, Oct 29, 2020 at 12:08 PM osalvador <osalvador@...e.de> wrote:
>
> On Thu, Oct 29, 2020 at 08:57:32AM -0700, Yang Shi wrote:
> > IMHO, we don't have to modify those two places at all. They are used
> > to rebalance the anon lru active/inactive ratio even if we did not try
> > to evict anon pages at all, so "total_swap_pages" is used instead of
> > checking swappiness and available swap space.
> >
> > The changes may result in imbalanced anon lru.
>
> I might be missing something, so bear with me.
>
> It is true that since we are only rebalancing the lists, we do not need to
> check for swap space yet, but here we are also adding a new end-point where we
> can migrate to in case of memory pressure.
>
> So in case we can demote pages, it makes sense to proceed with the aging
> and rebalancing regardless of whether we have swap in place, right?

Yes, makes sense. I missed that point.

>
> But maybe the right procedure would be to perform some sort of the
> following check in those two places:
>
>         if (total_swap_pages || can_migrate_to_demote_node)
>                 - proceed_with_rebalancing_or_aging

Looks sane to me.

>
> --
> Oscar Salvador
> SUSE L3