linux-kernel - Re: [External] Re: [RESEND PATCH v2 00/12] Convert all vmstat counters to pages or bytes

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Message-ID: <alpine.LSU.2.11.2012071218540.9574@eggly.anvils>
Date:   Mon, 7 Dec 2020 12:33:18 -0800 (PST)
From:   Hugh Dickins <hughd@...gle.com>
To:     Roman Gushchin <guro@...com>
cc:     Michal Hocko <mhocko@...e.com>,
        Muchun Song <songmuchun@...edance.com>,
        Greg KH <gregkh@...uxfoundation.org>, rafael@...nel.org,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Hugh Dickins <hughd@...gle.com>, Will Deacon <will@...nel.org>,
        Mike Rapoport <rppt@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>, esyr@...hat.com,
        peterx@...hat.com, krisman@...labora.com,
        Suren Baghdasaryan <surenb@...gle.com>, avagin@...nvz.org,
        Marco Elver <elver@...gle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Cgroups <cgroups@...r.kernel.org>
Subject: Re: [External] Re: [RESEND PATCH v2 00/12] Convert all vmstat counters
 to pages or bytes

On Mon, 7 Dec 2020, Roman Gushchin wrote:
> On Mon, Dec 07, 2020 at 04:02:54PM +0100, Michal Hocko wrote:
> > 
> > As I've said the THP accounting change makes more sense to me because it
> > allows future changes which are already undergoing so there is more
> > merit in those.
> 
> +1
> And this part is absolutely trivial.

It does need to be recognized that, with these changes, every THP stats
update overflows the per-cpu counter, resorting to atomic global updates.
And I'd like to see that mentioned in the commit message.

But this change is consistent with 4.7's 8f182270dfec ("mm/swap.c: flush
lru pvecs on compound page arrival"): we accepted greater overhead for
greater accuracy back then, so I think it's okay to do so for THP stats.

Hugh