From: Christoph Hellwig <hch@infradead.org>
To: Alexandre Ghiti <alex@ghiti.fr>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-block@vger.kernel.org, cgroups@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
david@kernel.org, Johannes Weiner <hannes@cmpxchg.org>,
Yosry Ahmed <yosry@kernel.org>, Nhat Pham <nphamcs@gmail.com>,
Chengming Zhou <chengming.zhou@linux.dev>,
Jens Axboe <axboe@kernel.dk>, Tejun Heo <tj@kernel.org>,
Josef Bacik <josef@toxicpanda.com>, Chris Li <chrisl@kernel.org>,
Kairui Song <kasong@tencent.com>,
Kemeng Shi <shikemeng@huaweicloud.com>,
Baoquan He <baoquan.he@linux.dev>, Barry Song <baohua@kernel.org>,
Youngjun Park <youngjun.park@lge.com>
Subject: Re: [RFC PATCH 1/4] block: do not issue background swap bios as root
Date: Mon, 28 Sep 2026 02:44:17 -0700 [thread overview]
Message-ID: <aro28ZGuYgmNg_n5@infradead.org> (raw)
In-Reply-To: <20260928081900.4187482-2-alex@ghiti.fr>
On Mon, Sep 28, 2026 at 10:18:36AM +0200, Alexandre Ghiti wrote:
> bio_issue_as_root_blkg() issues every REQ_SWAP bio as root, bypassing
> the cgroup IO controllers, because reclaim cannot stall indefinitely on
> swap writes. Some swap writes are not urgent though: zswap writeback is
> best effort.
>
> Such a bio cannot simply drop REQ_SWAP: dm-crypt and dm-thin rely on it
> for limit_swap_bios, which caps in-flight swap bios to avoid a memory
> deadlock, see commit a666e5c05e7c ("dm: fix deadlock when swapping to
> encrypted device").
Is that true? REQ_BACKGROUND very much implies the I/O can the throttled
and thus better not be foreground paging, and thus the caller should be
able to tolerate a failure.
next prev parent reply other threads:[~2026-09-28 9:44 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-28 8:18 [RFC PATCH 0/4] mm/zswap: make shrinker writeback work with iocost Alexandre Ghiti
2026-09-28 8:18 ` [RFC PATCH 1/4] block: do not issue background swap bios as root Alexandre Ghiti
2026-09-28 9:44 ` Christoph Hellwig [this message]
2026-09-28 8:18 ` [RFC PATCH 2/4] mm/zswap: turn shrink_memcg_cb()'s argument into a flags word Alexandre Ghiti
2026-09-28 8:18 ` [RFC PATCH 3/4] mm/zswap: allow writeback to be throttled by the cgroup IO controllers Alexandre Ghiti
2026-09-28 8:18 ` [RFC PATCH 4/4] mm/zswap: move reclaim-driven writeback to a kworker Alexandre Ghiti
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=aro28ZGuYgmNg_n5@infradead.org \
--to=hch@infradead.org \
--cc=akpm@linux-foundation.org \
--cc=alex@ghiti.fr \
--cc=axboe@kernel.dk \
--cc=baohua@kernel.org \
--cc=baoquan.he@linux.dev \
--cc=cgroups@vger.kernel.org \
--cc=chengming.zhou@linux.dev \
--cc=chrisl@kernel.org \
--cc=david@kernel.org \
--cc=hannes@cmpxchg.org \
--cc=josef@toxicpanda.com \
--cc=kasong@tencent.com \
--cc=linux-block@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=nphamcs@gmail.com \
--cc=shikemeng@huaweicloud.com \
--cc=tj@kernel.org \
--cc=yosry@kernel.org \
--cc=youngjun.park@lge.com \
/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
all inboxes | Powered by JetHome®