From: Andy Lutomirski <luto@kernel.org>
To: Nicholas Piggin <npiggin@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>
Cc: Randy Dunlap <rdunlap@infradead.org>,
linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org,
Anton Blanchard <anton@ozlabs.org>
Subject: Re: [PATCH v4 2/4] lazy tlb: allow lazy tlb mm refcounting to be configurable
Date: Tue, 8 Jun 2021 09:20:05 -0700 [thread overview]
Message-ID: <8ac1d420-b861-f586-bacf-8c3949e9b5c4@kernel.org> (raw)
In-Reply-To: <20210605014216.446867-3-npiggin@gmail.com>
On 6/4/21 6:42 PM, Nicholas Piggin wrote:
> Add CONFIG_MMU_TLB_REFCOUNT which enables refcounting of the lazy tlb mm
> when it is context switched. This can be disabled by architectures that
> don't require this refcounting if they clean up lazy tlb mms when the
> last refcount is dropped. Currently this is always enabled, which is
> what existing code does, so the patch is effectively a no-op.
>
> Rename rq->prev_mm to rq->prev_lazy_mm, because that's what it is.
I am in favor of this approach, but I would be a lot more comfortable
with the resulting code if task->active_mm were at least better
documented and possibly even guarded by ifdefs.
x86 bare metal currently does not need the core lazy mm refcounting, and
x86 bare metal *also* does not need ->active_mm. Under the x86 scheme,
if lazy mm refcounting were configured out, ->active_mm could become a
dangling pointer, and this makes me extremely uncomfortable.
So I tend to think that, depending on config, the core code should
either keep ->active_mm [1] alive or get rid of it entirely.
[1] I don't really think it belongs in task_struct at all. It's not a
property of the task. It's the *per-cpu* mm that the core code is
keeping alive for lazy purposes. How about consolidating it with the
copy in rq?
I guess the short summary of my opinion is that I like making this
configurable, but I do not like the state of the code.
--Andy
next prev parent reply other threads:[~2021-06-08 16:20 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-05 1:42 [PATCH v4 0/4] shoot lazy tlbs Nicholas Piggin
2021-06-05 1:42 ` [PATCH v4 1/4] lazy tlb: introduce lazy mm refcount helper functions Nicholas Piggin
2021-06-07 23:49 ` Andrew Morton
2021-06-08 1:39 ` Nicholas Piggin
2021-06-08 1:48 ` Andrew Morton
2021-06-08 4:11 ` Nicholas Piggin
2021-06-05 1:42 ` [PATCH v4 2/4] lazy tlb: allow lazy tlb mm refcounting to be configurable Nicholas Piggin
2021-06-08 3:11 ` Nicholas Piggin
2021-06-08 16:20 ` Andy Lutomirski [this message]
2021-06-14 0:45 ` Nicholas Piggin
2021-06-14 3:52 ` Andy Lutomirski
2021-06-14 4:14 ` Nicholas Piggin
2021-06-14 4:47 ` Nicholas Piggin
2021-06-14 5:21 ` Nicholas Piggin
2021-06-14 16:20 ` Andy Lutomirski
2021-06-15 0:55 ` Nicholas Piggin
2021-06-16 0:14 ` Andy Lutomirski
2021-06-16 1:02 ` Nicholas Piggin
2021-06-17 0:32 ` Nicholas Piggin
2021-06-05 1:42 ` [PATCH v4 3/4] lazy tlb: shoot lazies, a non-refcounting lazy tlb option Nicholas Piggin
2021-06-08 3:15 ` Nicholas Piggin
2021-06-05 1:42 ` [PATCH v4 4/4] powerpc/64s: enable MMU_LAZY_TLB_SHOOTDOWN Nicholas Piggin
2021-06-07 23:52 ` Andrew Morton
2021-06-08 2:13 ` Nicholas Piggin
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=8ac1d420-b861-f586-bacf-8c3949e9b5c4@kernel.org \
--to=luto@kernel.org \
--cc=akpm@linux-foundation.org \
--cc=anton@ozlabs.org \
--cc=linux-arch@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=npiggin@gmail.com \
--cc=rdunlap@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).