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Thu, 5 Sep 2024 18:21:50 +0000 (UTC) Date: Thu, 5 Sep 2024 20:21:46 +0200 (CEST) From: Mikulas Patocka To: Eric Biggers cc: dm-devel@lists.linux.dev, Alasdair Kergon , Mike Snitzer , Tejun Heo , Lai Jiangshan , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Sami Tolvanen Subject: Re: [PATCH] dm verity: don't use WQ_MEM_RECLAIM In-Reply-To: <20240904040444.56070-1-ebiggers@kernel.org> Message-ID: <086a76c4-98da-d9d1-9f2f-6249c3d55fe9@redhat.com> References: <20240904040444.56070-1-ebiggers@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 X-Rspam-User: X-Rspamd-Queue-Id: 85B0A4001C X-Rspamd-Server: rspam01 X-Stat-Signature: 349gcunrhkpneiuxpsnnq9p7snw9kfgf X-HE-Tag: 1725560519-386237 X-HE-Meta: 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 EseD6E3z +K9mHcbwlkMA1Uwy2KIUZ2XyolKxMS0ay5bUghOtMkZRJx1FGL1X8fsyP9PjGThemXCMo8rlHCyK0VM21JymAPyFTHGaQvznnxKFn7bVQc5iOSKXS7HyWmvZjxF5MajGHQ6hee2I2PsOj5d/X/Y/edLJb4/aj7LNotrjLfdPYOv39rVBQhBq1HprM+81Mf54q18qIHXa7pRkjZ/NjR1G77MYbkONE+sRgL3nx5Z/8syY862JTDalDs25RbqHlcaz37+hkKm7Tm8PLq2CBfldkA4wwlouZj02qDagcMSDAjVOVyf8zV5lGg2vU3Bu+hrJERwrD9CVHvV89BNp8eo78Y15H/XK/RJIozgBfd+u6Ca4ZIJNd9a1A2mPdNtIcphhTc+V+ X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 3 Sep 2024, Eric Biggers wrote: > From: Eric Biggers > > Since dm-verity doesn't support writes, the kernel's memory reclaim code > will never wait on dm-verity work. That makes the use of WQ_MEM_RECLAIM > in dm-verity unnecessary. WQ_MEM_RECLAIM has been present from the > beginning of dm-verity, but I could not find a justification for it; > I suspect it was just copied from dm-crypt which does support writes. > > Therefore, remove WQ_MEM_RECLAIM from dm-verity. This eliminates the > creation of an unnecessary rescuer thread per dm-verity device. > > Signed-off-by: Eric Biggers Hmm. I can think about a case where you have read-only dm-verity device, on the top of that you have dm-snapshot device and on the top of that you have a writable filesystem. When the filesystem needs to write data, it submits some write bios. When dm-snapshot receives these write bios, it will read from the dm-verity device and write to the snapshot's exception store device. So, dm-verity needs WQ_MEM_RECLAIM in this case. Mikulas > --- > drivers/md/dm-verity-target.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c > index cf659c8feb29f..051e84ca401dc 100644 > --- a/drivers/md/dm-verity-target.c > +++ b/drivers/md/dm-verity-target.c > @@ -1488,11 +1488,11 @@ static int verity_ctr(struct dm_target *ti, unsigned int argc, char **argv) > * Also as required for the "try_verify_in_tasklet" feature: WQ_HIGHPRI > * allows verify_wq to preempt softirq since verification in BH workqueue > * will fall-back to using it for error handling (or if the bufio cache > * doesn't have required hashes). > */ > - v->verify_wq = alloc_workqueue("kverityd", WQ_MEM_RECLAIM | WQ_HIGHPRI, 0); > + v->verify_wq = alloc_workqueue("kverityd", WQ_HIGHPRI, 0); > if (!v->verify_wq) { > ti->error = "Cannot allocate workqueue"; > r = -ENOMEM; > goto bad; > } > > base-commit: 88fac17500f4ea49c7bac136cf1b27e7b9980075 > -- > 2.46.0 >