From: Pedro Gomes <pedrodemargomes@gmail.com>
To: David Hildenbrand <david@redhat.com>
Cc: SeongJae Park <sj@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
John Hubbard <jhubbard@nvidia.com>
Subject: Re: [PATCH] mm/damon: Add option to monitor only writes
Date: Mon, 7 Feb 2022 23:05:03 -0300 [thread overview]
Message-ID: <CACpbsfapGSbno_n7ZJYJ2E4KkqWdWe_Wz8PuECBa3PZBp2Xnxw@mail.gmail.com> (raw)
In-Reply-To: <c4128a09-1dc7-24b3-8ff2-eaf61f3de5e5@redhat.com>
On Mon, Feb 7, 2022 at 7:32 AM David Hildenbrand <david@redhat.com> wrote:
>
> Just like clearrefs, this can race against GUP-fast to detect pinned
> pages. And just like clearrefs, we're not handling PMDs properly. And
> just like anything that write-protects random anon pages right now, this
> does not consider O_DIRECT as is.
>
> Fortunately, there are not too many users of clearreefs/softdirty
> tracking out there (my search a while ago returned no open source
> users). My assumption is that your feature might see more widespread use.
>
> Adding more random write protection until we fixed the COW issues [1]
> really makes my stomach hurt on a Monday morning.
I was not aware of these issues.
> Please, let's defer any more features that rely on write-protecting
> random anon pages until we have ways in place to not corrupt random user
> space.
>
> That is:
> 1) Teaching the COW logic to not copy pages that are pinned -- I'm
> working on that.
> 2) Converting O_DIRECT to use FOLL_PIN instead of FOLL_GET. John is
> working on that.
>
> So I'm not against this change. I'm against this change at this point in
> time.
I agree. I will wait until the COW problems are solved to send this patch.
--
Atenciosamente,
Pedro Demarchi Gomes.
next prev parent reply other threads:[~2022-02-08 2:09 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-03 13:12 [PATCH] mm/damon: Add option to monitor only writes Pedro Demarchi Gomes
2022-02-03 13:39 ` SeongJae Park
2022-02-04 15:11 ` Pedro Gomes
2022-02-07 8:16 ` SeongJae Park
2022-02-04 1:29 ` kernel test robot
2022-02-04 1:29 ` kernel test robot
2022-02-04 1:30 ` kernel test robot
2022-02-07 10:32 ` David Hildenbrand
2022-02-08 2:05 ` Pedro Gomes [this message]
2022-02-08 9:01 ` David Hildenbrand
2022-02-08 13:18 ` Pedro Gomes
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