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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20210128055221.GA3166@localhost.localdomain>
Date:   Thu, 28 Jan 2021 06:52:21 +0100
From:   Oscar Salvador <osalvador@...e.de>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     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>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v3 3/5] hugetlb: only set HPageMigratable for migratable
 hstates

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.

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

Thanks

-- 
Oscar Salvador
SUSE L3