From: Dan Schatzberg <schatzberg.dan@gmail.com>
To: "Michal Koutný" <mkoutny@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
"open list:BLOCK LAYER" <linux-block@vger.kernel.org>,
open list <linux-kernel@vger.kernel.org>,
"open list:CONTROL GROUP (CGROUP)" <cgroups@vger.kernel.org>,
"open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Jens Axboe <axboe@kernel.dk>
Subject: Re: [PATCH 3/3] loop: Charge i/o to mem and blk cg
Date: Tue, 29 Jun 2021 10:03:33 -0400 [thread overview]
Message-ID: <YNsoNeQNMmdplmtp@dschatzberg-fedora-PC0Y6AEN> (raw)
In-Reply-To: <YNr1TYfBwR/tEpEJ@blackbook>
> Non-inlining in the loop module doesn't seem like a big trouble. OTOH,
> other callers may be more sensitive and would need to rely on inlining.
Yes, this is my concern as well.
> I can't currently think of a nice way to have both the exported and the
> exlicitly inlined variant at once. It seems it's either API or perf
> craft in the end but both are uncertain, so I guess the current approach
> is fine in the end.
>
> > Yes it is intentional. All requests (not just aio) go through the loop
> > worker which grabs the blkcg reference in loop_queue_work() on
> > construction. So I believe grabbing a reference per request is
> > unnecessary.
>
> Isn't there a window without the reference between loop_queue_rq and
> loop_queue_work?
Hmm, perhaps I'm not understanding how the reference counting works,
but my understanding is that we enter loop_queue_rq with presumably
some code earlier holding a reference to the blkcg, we only need to
acquire a reference sometime before returning from loop_queue_rq. The
"window" between loop_queue_rq and loop_queue_work is all
straight-line code so there's no possibility for the earlier code to
get control back and drop the reference.
> I don't know, you seem to know better, so I'd suggest
> dropping a comment line into the code explaining this.
I wouldn't be so sure that I know any better here :D - I'm fairly
inexperienced in this domain.
Where would you suggest putting such a comment? The change in question
removed a particular case where we explicitly grab a reference to the
blkcg because now we do it uniformly in one place. Would you like a
comment explaining why we acquire a reference for all loop workers or
one explaining specifically why we don't need to acquire one for aio?
next prev parent reply other threads:[~2021-06-29 14:03 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-10 17:39 [PATCH V14 0/3] Charge loop device i/o to issuing cgroup Dan Schatzberg
2021-06-10 17:39 ` [PATCH 1/3] loop: Use worker per cgroup instead of kworker Dan Schatzberg
2021-06-10 17:39 ` [PATCH 2/3] mm: Charge active memcg when no mm is set Dan Schatzberg
2021-06-25 14:47 ` Michal Koutný
2021-06-10 17:39 ` [PATCH 3/3] loop: Charge i/o to mem and blk cg Dan Schatzberg
2021-06-25 15:01 ` Michal Koutný
2021-06-28 14:17 ` Dan Schatzberg
2021-06-29 10:26 ` Michal Koutný
2021-06-29 14:03 ` Dan Schatzberg [this message]
2021-06-30 9:42 ` Michal Koutný
2021-06-30 14:49 ` Dan Schatzberg
-- strict thread matches above, loose matches on Subject: below --
2021-06-03 14:57 [PATCH V13 0/3] Charge loop device i/o to issuing cgroup Dan Schatzberg
2021-06-03 14:57 ` [PATCH 3/3] loop: Charge i/o to mem and blk cg Dan Schatzberg
2021-04-02 19:16 [PATCH V12 0/3] Charge loop device i/o to issuing cgroup Dan Schatzberg
2021-04-02 19:16 ` [PATCH 3/3] loop: Charge i/o to mem and blk cg Dan Schatzberg
2021-04-06 3:23 ` Ming Lei
2021-03-29 14:48 [PATCH V11 0/3] Charge loop device i/o to issuing cgroup Dan Schatzberg
2021-03-29 14:48 ` [PATCH 3/3] loop: Charge i/o to mem and blk cg Dan Schatzberg
2021-03-16 15:36 [PATCH v10 0/3] Charge loop device i/o to issuing cgroup Dan Schatzberg
2021-03-16 15:36 ` [PATCH 3/3] loop: Charge i/o to mem and blk cg Dan Schatzberg
2021-03-16 16:25 ` Shakeel Butt
2020-08-31 15:36 [PATCH v8 0/3] Charge loop device i/o to issuing cgroup Dan Schatzberg
2020-08-31 15:37 ` [PATCH 3/3] loop: Charge i/o to mem and blk cg Dan Schatzberg
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