From: Luis Chamberlain <mcgrof@kernel.org>
To: Keith Busch <kbusch@kernel.org>
Cc: Bart Van Assche <bvanassche@acm.org>,
Christoph Hellwig <hch@lst.de>,
linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
linux-block@vger.kernel.org, lsf-pc@lists.linux-foundation.org,
david@fromorbit.com, leon@kernel.org, sagi@grimberg.me,
axboe@kernel.dk, joro@8bytes.org, brauner@kernel.org,
hare@suse.de, willy@infradead.org, djwong@kernel.org,
john.g.garry@oracle.com, ritesh.list@gmail.com,
p.raghav@samsung.com, gost.dev@samsung.com, da.gomez@samsung.com
Subject: Re: [LSF/MM/BPF TOPIC] breaking the 512 KiB IO boundary on x86_64
Date: Thu, 20 Mar 2025 14:46:20 -0700 [thread overview]
Message-ID: <Z9yMrCtwtX7xIMMx@bombadil.infradead.org> (raw)
In-Reply-To: <Z9w7Nz-CxWSqj__H@kbusch-mbp.dhcp.thefacebook.com>
On Thu, Mar 20, 2025 at 09:58:47AM -0600, Keith Busch wrote:
> I allocate out of hugetlbfs to reliably send direct IO at this size
> because the nvme driver's segment count is limited to 128. The driver
> doesn't impose a segment size limit, though. If each segment is only 4k
> (a common occurance), I guess that's where Luis is getting the 512K
> limit?
Right, for direct IO we are not getting the large folios we can take
fruit from with buffered IO, so in effect we can end up with large IOs
possible with buffered but not direct IO.
Yes, direct IO with huge pages can help you overcome this as you noted.
But also mTHP can be enabled and used for direct IO, or io-uring cmd but
mTHP is not deterministic for your allocations even if you have a min
order filesystem. The min order requirement is only useful to use in the
buffered IO case.
Luis
next prev parent reply other threads:[~2025-03-20 21:46 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-03-20 11:41 Luis Chamberlain
2025-03-20 12:11 ` Matthew Wilcox
2025-03-20 13:29 ` Daniel Gomez
2025-03-20 14:31 ` Matthew Wilcox
2025-03-20 13:47 ` Daniel Gomez
2025-03-20 14:54 ` Christoph Hellwig
2025-03-21 9:14 ` Daniel Gomez
2025-03-20 14:18 ` Christoph Hellwig
2025-03-20 15:37 ` Bart Van Assche
2025-03-20 15:58 ` Keith Busch
2025-03-20 16:13 ` Kanchan Joshi
2025-03-20 16:38 ` Christoph Hellwig
2025-03-20 21:50 ` Luis Chamberlain
2025-03-20 21:46 ` Luis Chamberlain [this message]
2025-03-20 21:40 ` Luis Chamberlain
2025-03-20 18:46 ` Ritesh Harjani
2025-03-20 21:30 ` Darrick J. Wong
2025-03-21 2:13 ` Ritesh Harjani
2025-03-21 3:05 ` Darrick J. Wong
2025-03-21 4:56 ` Theodore Ts'o
2025-03-21 5:00 ` Christoph Hellwig
2025-03-21 18:39 ` Ritesh Harjani
2025-03-21 16:38 ` Keith Busch
2025-03-21 17:21 ` Ritesh Harjani
2025-03-21 18:55 ` Keith Busch
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