Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Zi Yan <ziy@nvidia.com>
To:     David Hildenbrand <david@redhat.com>
CC:     <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Minchan Kim <minchan@kernel.org>,
        Oscar Salvador <osalvador@suse.de>,
        Michal Hocko <mhocko@kernel.org>,
        Vlastimil Babka <vbabka@suse.cz>
Subject: Re: [PATCH v1] mm/page_alloc: drop pr_info_ratelimited() in
 alloc_contig_range()
Date:   Mon, 1 Mar 2021 10:35:22 -0500
Message-ID: <395622C6-F8D9-408D-B35B-17B16F1B5E77@nvidia.com>
In-Reply-To: <20210301150945.77012-1-david@redhat.com>
References: <20210301150945.77012-1-david@redhat.com>
MIME-Version: 1.0
Content-Type: multipart/signed;
        boundary="=_MailMate_4DE8FF03-D3CA-4DB3-A579-7B9830E8D138_=";
        micalg=pgp-sha512; protocol="application/pgp-signature"
Precedence: bulk

--=_MailMate_4DE8FF03-D3CA-4DB3-A579-7B9830E8D138_=
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On 1 Mar 2021, at 10:09, David Hildenbrand wrote:

> The information that some PFNs are busy is:
> a) not helpful for ordinary users: we don't even know *who* called
>    alloc_contig_range(). This is certainly not worth a pr_info.*().
> b) not really helpful for debugging: we don't have any details *why*
>    these PFNs are busy, and that is what we usually care about.
> c) not complete: there are other cases where we fail alloc_contig_range=
()
>    using different paths that are not getting recorded.
>
> For example, we reach this path once we succeeded in isolating pagebloc=
ks,
> but failed to migrate some pages - which can happen easily on
> ZONE_NORMAL (i.e., has_unmovable_pages() is racy) but also on ZONE_MOVA=
BLE
> i.e., we would have to retry longer to migrate).
>
> For example via virtio-mem when unplugging memory, we can create quite
> some noise (especially with ZONE_NORMAL) that is not of interest to
> users - it's expected that some allocations may fail as memory is busy.=

>
> Let's just drop that pr_info_ratelimit() and rather implement a dynamic=

> debugging mechanism in the future that can give us a better reason why
> alloc_contig_range() failed on specific pages.
>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---

LGTM. I agree that the printout is not quite useful.

Reviewed-by: Zi Yan <ziy@nvidia.com>


=E2=80=94
Best Regards,
Yan Zi

--=_MailMate_4DE8FF03-D3CA-4DB3-A579-7B9830E8D138_=
Content-Description: OpenPGP digital signature
Content-Disposition: attachment; filename="signature.asc"
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----
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=DMSI
-----END PGP SIGNATURE-----

--=_MailMate_4DE8FF03-D3CA-4DB3-A579-7B9830E8D138_=--