linux-kernel - Re: [PATCH v3 3/5] hugetlb: only set HPageMigratable for migratable hstates

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Message-Id: <20210128133733.ce1fb2eac98ab5696c08f288@linux-foundation.org>
Date:   Thu, 28 Jan 2021 13:37:33 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Michal Hocko <mhocko@...e.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Muchun Song <songmuchun@...edance.com>,
        David Hildenbrand <david@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Miaohe Lin <linmiaohe@...wei.com>
Subject: Re: [PATCH v3 3/5] hugetlb: only set HPageMigratable for migratable
 hstates

On Thu, 28 Jan 2021 06:52:21 +0100 Oscar Salvador <osalvador@...e.de> wrote:

> On Wed, Jan 27, 2021 at 03:36:41PM -0800, Mike Kravetz wrote:
> > Yes, this patch is somewhat optional.  It should be a minor improvement
> > in cases where we are dealing with hpages in a non-migratable hstate.
> > Although, I do not believe this is the common case.
> > 
> > The real reason for even looking into this was a comment by Oscar.  With
> > the name change to HPageMigratable, it implies that the page is migratable.
> > However, this is not the case if the page's hstate does not support migration.
> > So, if we check the hstate when setting the flag we can eliminate those
> > cases where the page is certainly not migratable.
> > 
> > I don't really love this patch.  It has minimal functional value.
> > 
> > Oscar, what do you think about dropping this?
> 
> Yeah, I remember this topic arose during a discussion of patch#2 in the
> early versions, about whether the renaming to HPageMigratable made
> sense.
> 
> Back then I thought that we could have this in one place at fault-path [1],
> which should have made this prettier, but it is not the case.
> True is that the optimization is little, so I am fine with dropping this
> patch.

I've dropped it.

> unmap_and_move_huge_page() fences off pages belonging to non-migratable
> hstates.
> 
> [1] https://patchwork.kernel.org/project/linux-mm/patch/20210120013049.311822-3-mike.kravetz@oracle.com/#23914033