From: "Paul E. McKenney" <paulmck@kernel.org>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: Vlastimil Babka <vbabka@suse.cz>,
rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
rushikesh.s.kadam@intel.com, urezki@gmail.com,
neeraj.iitr10@gmail.com, frederic@kernel.org,
rostedt@goodmis.org, vineeth@bitbyteword.org,
boqun.feng@gmail.com, Hyeonggon Yoo <42.hyeyoo@gmail.com>
Subject: Re: [PATCH v5 02/18] mm/sl[au]b: rearrange struct slab fields to allow larger rcu_head
Date: Sat, 3 Sep 2022 06:53:10 -0700 [thread overview]
Message-ID: <20220903135310.GS6159@paulmck-ThinkPad-P17-Gen-1> (raw)
In-Reply-To: <013ca416-72de-8059-a5d5-cd63c92ef119@joelfernandes.org>
On Fri, Sep 02, 2022 at 11:09:08AM -0400, Joel Fernandes wrote:
>
>
> On 9/2/2022 5:30 AM, Vlastimil Babka wrote:
> > On 9/2/22 11:26, Vlastimil Babka wrote:
> >> On 9/2/22 00:17, Joel Fernandes (Google) wrote:
> >>> From: Vlastimil Babka <vbabka@suse.cz>
> >>>
> >>> Joel reports [1] that increasing the rcu_head size for debugging
> >>> purposes used to work before struct slab was split from struct page, but
> >>> now runs into the various SLAB_MATCH() sanity checks of the layout.
> >>>
> >>> This is because the rcu_head in struct page is in union with large
> >>> sub-structures and has space to grow without exceeding their size, while
> >>> in struct slab (for SLAB and SLUB) it's in union only with a list_head.
> >>>
> >>> On closer inspection (and after the previous patch) we can put all
> >>> fields except slab_cache to a union with rcu_head, as slab_cache is
> >>> sufficient for the rcu freeing callbacks to work and the rest can be
> >>> overwritten by rcu_head without causing issues.
> >>>
> >>> This is only somewhat complicated by the need to keep SLUB's
> >>> freelist+counters aligned for cmpxchg_double. As a result the fields
> >>> need to be reordered so that slab_cache is first (after page flags) and
> >>> the union with rcu_head follows. For consistency, do that for SLAB as
> >>> well, although not necessary there.
> >>>
> >>> As a result, the rcu_head field in struct page and struct slab is no
> >>> longer at the same offset, but that doesn't matter as there is no
> >>> casting that would rely on that in the slab freeing callbacks, so we can
> >>> just drop the respective SLAB_MATCH() check.
> >>>
> >>> Also we need to update the SLAB_MATCH() for compound_head to reflect the
> >>> new ordering.
> >>>
> >>> While at it, also add a static_assert to check the alignment needed for
> >>> cmpxchg_double so mistakes are found sooner than a runtime GPF.
> >>>
> >>> [1] https://lore.kernel.org/all/85afd876-d8bb-0804-b2c5-48ed3055e702@joelfernandes.org/
> >>>
> >>> Reported-by: Joel Fernandes <joel@joelfernandes.org>
> >>> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> >>
> >> I've added patches 01 and 02 to slab tree for -next exposure before Joel's
> >> full series posting, but it should be also ok if rcu tree carries them with
> >> the whole patchset. I can then drop them from slab tree (there are no
> >> dependencies with other stuff there) so we don't introduce duplicite commits
> >> needlessly, just give me a heads up.
> >
> > Ah but in that case please apply the reviews from my posting [1]
> >
> > patch 1:
> > Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
> >
> > patch 2
> > Acked-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
> >
> > [1] https://lore.kernel.org/all/20220826090912.11292-1-vbabka@suse.cz/
>
>
> Sorry for injecting confusion - my main intent with including the mm patches in
> this series is to make it easier for other reviewers/testers to backport the
> series to their kernels in one shot. Some reviewers expressed interested in
> trying out the series.
>
> I think it is best to let the -mm patches in the series go through the slab
> tree, as you also have the Acks/Reviews there and will take sure those
> dependencies are out of the way.
>
> My lesson here is to be more clear, I could have added some notes for context
> below the "---" of those mm patches.
>
> Thanks again for your help,
Hello, Vlastimil, and thank you for putting these together!
I believe that your two patches should go in via the slab tree.
I am queueing them in -rcu only temporarily and just for convenience
in testing. I expect that I will rebase them so that I can let your
versions cover things in -next.
Thanx, Paul
next prev parent reply other threads:[~2022-09-03 13:53 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-01 22:17 [PATCH v5 00/18] Implement call_rcu_lazy() and miscellaneous fixes Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 01/18] mm/slub: perform free consistency checks before call_rcu Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 02/18] mm/sl[au]b: rearrange struct slab fields to allow larger rcu_head Joel Fernandes (Google)
2022-09-02 9:26 ` Vlastimil Babka
2022-09-02 9:30 ` Vlastimil Babka
2022-09-02 15:09 ` Joel Fernandes
2022-09-03 13:53 ` Paul E. McKenney [this message]
2022-09-01 22:17 ` [PATCH v5 03/18] rcu/tree: Use READ_ONCE() for lockless read of rnp->qsmask Joel Fernandes (Google)
2022-09-06 22:26 ` Boqun Feng
2022-09-06 22:31 ` Joel Fernandes
2022-09-01 22:17 ` [PATCH v5 04/18] rcu: Fix late wakeup when flush of bypass cblist happens Joel Fernandes (Google)
2022-09-02 11:35 ` Frederic Weisbecker
2022-09-02 23:58 ` Joel Fernandes
2022-09-03 15:10 ` Paul E. McKenney
2022-09-04 21:13 ` Frederic Weisbecker
2022-09-03 14:04 ` Paul E. McKenney
2022-09-03 14:05 ` Joel Fernandes
2022-09-06 3:07 ` Joel Fernandes
2022-09-06 9:48 ` Frederic Weisbecker
2022-09-07 2:43 ` Joel Fernandes
2022-09-01 22:17 ` [PATCH v5 05/18] rcu: Move trace_rcu_callback() before bypassing Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 06/18] rcu: Introduce call_rcu_lazy() API implementation Joel Fernandes (Google)
2022-09-02 15:21 ` Frederic Weisbecker
2022-09-02 23:09 ` Joel Fernandes
2022-09-05 12:59 ` Frederic Weisbecker
2022-09-05 20:18 ` Joel Fernandes
2022-09-05 20:32 ` Joel Fernandes
2022-09-06 8:55 ` Paul E. McKenney
2022-09-06 16:16 ` Joel Fernandes
2022-09-06 17:05 ` Paul E. McKenney
2022-09-03 22:00 ` Joel Fernandes
2022-09-04 21:01 ` Frederic Weisbecker
2022-09-05 20:20 ` Joel Fernandes
2022-09-06 3:05 ` Joel Fernandes
2022-09-06 15:17 ` Frederic Weisbecker
2022-09-06 16:15 ` Joel Fernandes
2022-09-06 16:31 ` Joel Fernandes
2022-09-06 16:38 ` Joel Fernandes
2022-09-06 16:43 ` Joel Fernandes
2022-09-06 19:11 ` Frederic Weisbecker
2022-09-07 2:56 ` Joel Fernandes
2022-09-07 9:56 ` Frederic Weisbecker
2022-09-07 10:03 ` Frederic Weisbecker
2022-09-07 14:01 ` Joel Fernandes
2022-09-07 0:06 ` Joel Fernandes
2022-09-07 9:40 ` Frederic Weisbecker
2022-09-07 13:44 ` Joel Fernandes
2022-09-07 15:38 ` Frederic Weisbecker
2022-09-07 15:39 ` Joel Fernandes
2022-09-21 23:52 ` Joel Fernandes
2022-09-06 18:16 ` Uladzislau Rezki
2022-09-06 18:21 ` Joel Fernandes
2022-09-07 8:52 ` Uladzislau Rezki
2022-09-07 15:23 ` Joel Fernandes
2022-09-03 14:03 ` Paul E. McKenney
2022-09-03 14:05 ` Joel Fernandes
2022-09-01 22:17 ` [PATCH v5 07/18] rcu: shrinker for lazy rcu Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 08/18] rcu: Add per-CB tracing for queuing, flush and invocation Joel Fernandes (Google)
2022-09-02 16:48 ` kernel test robot
2022-09-03 12:39 ` Paul E. McKenney
2022-09-03 14:07 ` Joel Fernandes
2022-09-02 19:01 ` kernel test robot
2022-09-01 22:17 ` [PATCH v5 09/18] rcuscale: Add laziness and kfree tests Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 10/18] rcutorture: Add test code for call_rcu_lazy() Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 11/18] fs: Move call_rcu() to call_rcu_lazy() in some paths Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 12/18] cred: Move call_rcu() to call_rcu_lazy() Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 13/18] security: " Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 14/18] net/core: " Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 15/18] kernel: Move various core kernel usages " Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 16/18] lib: Move call_rcu() " Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 17/18] i915: " Joel Fernandes (Google)
2022-09-01 22:17 ` [PATCH v5 18/18] fork: Move thread_stack_free_rcu() " Joel Fernandes (Google)
2022-09-03 15:22 ` [PATCH v5 00/18] Implement call_rcu_lazy() and miscellaneous fixes Paul E. McKenney
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=20220903135310.GS6159@paulmck-ThinkPad-P17-Gen-1 \
--to=paulmck@kernel.org \
--cc=42.hyeyoo@gmail.com \
--cc=boqun.feng@gmail.com \
--cc=frederic@kernel.org \
--cc=joel@joelfernandes.org \
--cc=linux-kernel@vger.kernel.org \
--cc=neeraj.iitr10@gmail.com \
--cc=rcu@vger.kernel.org \
--cc=rostedt@goodmis.org \
--cc=rushikesh.s.kadam@intel.com \
--cc=urezki@gmail.com \
--cc=vbabka@suse.cz \
--cc=vineeth@bitbyteword.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).