From: Logan Gunthorpe <logang@deltatee.com>
To: Mykola Marzhan <mykola@meshstor.io>, Jens Axboe <axboe@kernel.dk>,
Song Liu <song@kernel.org>, Yu Kuai <yukuai@fygo.io>,
Keith Busch <kbusch@kernel.org>, Christoph Hellwig <hch@lst.de>,
Sagi Grimberg <sagi@grimberg.me>,
linux-block@vger.kernel.org, linux-raid@vger.kernel.org,
linux-nvme@lists.infradead.org
Cc: Li Nan <magiclinan@didiglobal.com>, Xiao Ni <xiao@kernel.org>,
Guoqing Jiang <guoqing.jiang@linux.dev>,
Leon Romanovsky <leon@kernel.org>, Jason Gunthorpe <jgg@ziepe.ca>,
Kiran Kumar Modukuri <kmodukuri@nvidia.com>,
Chaitanya Kulkarni <kch@nvidia.com>,
Bjorn Helgaas <bhelgaas@google.com>,
Shivaji Kant <shivajikant@google.com>,
Pranjal Shrivastava <praan@google.com>,
Henrique Carvalho <henrique.carvalho@suse.com>,
linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org,
linux-pci@vger.kernel.org
Subject: Re: [PATCH v2 4/7] md/raid1: don't use write-behind for P2PDMA bios
Date: Mon, 20 Jul 2026 10:31:45 -0600 [thread overview]
Message-ID: <66e72dfa-cb03-49ea-ac52-cb171edef6e4@deltatee.com> (raw)
In-Reply-To: <20260719105327.864949-5-mykola@meshstor.io>
On 2026-07-19 04:53, Mykola Marzhan wrote:
> alloc_behind_master_bio() copies the bio's data with bio_copy_data(),
> a CPU copy. P2PDMA pages are peer device (BAR) memory; generic code
> must not assume CPU load/store access to them is safe or fast on
> every architecture, and bouncing peer memory through the CPU defeats
> the point of a peer-to-peer transfer.
>
> Skip write-behind for P2PDMA bios: they are written directly to all
> members, including write-mostly ones. Ordering against write-behind
> I/O in flight to overlapping sectors is preserved: the non-behind
> clone path serializes on CollisionCheck rdevs (see the preceding
> fix), which covers these bios like any other write that bypasses
> write-behind.
>
> Fixes: 02666132403a ("md: propagate BLK_FEAT_PCI_P2PDMA from member devices to RAID device")
> Assisted-by: Claude:claude-opus-4-8
> Signed-off-by: Mykola Marzhan <mykola@meshstor.io>
Looks correct to me.
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
next prev parent reply other threads:[~2026-07-20 16:32 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-19 10:53 [PATCH v2 0/7] block,md,nvme: correct handling of unsupported P2PDMA transfers Mykola Marzhan
2026-07-19 10:53 ` [PATCH v2 1/7] blk-mq-dma: restore BLK_STS_TARGET for unsupported P2P transfers Mykola Marzhan
2026-07-19 11:01 ` sashiko-bot
2026-07-20 14:49 ` Christoph Hellwig
[not found] ` <CAPzsNDv6hUV3gHdaxuwjRcr4couUKq_M5DKObFNaYqCHnm7ZMw@mail.gmail.com>
2026-07-20 18:42 ` Logan Gunthorpe
2026-07-20 18:49 ` Logan Gunthorpe
2026-07-21 17:49 ` Mykola Marzhan
2026-07-19 10:53 ` [PATCH v2 2/7] md: ensure REQ_NOMERGE is set on P2PDMA bios Mykola Marzhan
2026-07-19 11:02 ` sashiko-bot
2026-07-19 10:53 ` [PATCH v2 3/7] md/raid1: serialize non-write-behind writes on CollisionCheck rdevs Mykola Marzhan
2026-07-19 11:08 ` sashiko-bot
2026-07-19 10:53 ` [PATCH v2 4/7] md/raid1: don't use write-behind for P2PDMA bios Mykola Marzhan
2026-07-19 11:05 ` sashiko-bot
2026-07-20 16:31 ` Logan Gunthorpe [this message]
2026-07-19 10:53 ` [PATCH v2 5/7] md/raid1,raid10: keep REQ_NOMERGE on narrow_write_error() retry clones Mykola Marzhan
2026-07-19 11:20 ` sashiko-bot
2026-07-20 16:32 ` Logan Gunthorpe
2026-07-19 10:53 ` [PATCH v2 6/7] md/raid1,raid10: skip futile retries on P2PDMA mapping failures Mykola Marzhan
2026-07-19 11:11 ` sashiko-bot
2026-07-20 16:49 ` Logan Gunthorpe
2026-07-21 17:50 ` Mykola Marzhan
2026-07-21 23:38 ` Logan Gunthorpe
2026-07-19 10:53 ` [PATCH v2 7/7] nvme-rdma: return BLK_STS_TARGET for unsupported P2P transfers Mykola Marzhan
2026-07-19 11:17 ` sashiko-bot
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