From: Christoph Hellwig <hch@infradead.org>
To: Qu Wenruo <quwenruo.btrfs@gmx.com>
Cc: Christoph Hellwig <hch@infradead.org>, Qu Wenruo <wqu@suse.com>,
linux-btrfs@vger.kernel.org, linux-block@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org
Subject: Re: [PATCH v3 3/4] iomap: reject NOWAIT and BOUNCE direct IOs
Date: Mon, 15 Jun 2026 22:19:46 -0700 [thread overview]
Message-ID: <ajDc8nFYyiQ66TOR@infradead.org> (raw)
In-Reply-To: <8a0e1881-fe73-4912-95f9-8eac998840d5@gmx.com>
On Tue, Jun 16, 2026 at 10:30:27AM +0930, Qu Wenruo wrote:
> After scanning the code for related memory allocation, there are some other
> locations doing memory allocation, including but not limited to:
>
> - iomap_dio_alloc_bio()
> This one is a little tricky, if we pass GFP_NOWAIT, we can break the
> old assumption that the function will always return a bio.
>
> - fscrypt_set_bio_crypt_ctx()
> This one is fine so far, as neither XFS nor btrfs support fscrypt yet.
>
> And any memory allocation failure in NOWAIT mode should return -EAGAIN, not
> -ENOMEM so that the caller can retry in blocking mode as a fallback.
>
> To me, considering NOWAIT itself is only an optimistic flag, and caller
> should always have a blocking mode as fallback, I'd prefer to reject NOWAIT
> + BOUNCE direct writes completely inside btrfs for now.
If you want to do that in btrfs please do it there.
> And leave all the missing NOWAIT handling in iomap in a dedicated series.
This might be worth looking into.
next prev parent reply other threads:[~2026-06-16 5:19 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-12 9:51 [PATCH v3 0/4] btrfs: use IOMAP_DIO_BOUNCE flag instead of falling back to buffered IO Qu Wenruo
2026-06-12 9:51 ` [PATCH v3 1/4] block: revert the iov_iter after a short copy in bio_iov_iter_bounce_write() Qu Wenruo
2026-06-15 15:03 ` Christoph Hellwig
2026-06-12 9:51 ` [PATCH v3 2/4] block: respect iov_iter::nofault flag " Qu Wenruo
2026-06-15 15:05 ` Christoph Hellwig
2026-06-12 9:51 ` [PATCH v3 3/4] iomap: reject NOWAIT and BOUNCE direct IOs Qu Wenruo
2026-06-15 15:05 ` Christoph Hellwig
2026-06-15 22:43 ` Qu Wenruo
2026-06-16 1:00 ` Qu Wenruo
2026-06-16 5:19 ` Christoph Hellwig [this message]
2026-06-16 5:18 ` Christoph Hellwig
2026-06-12 9:51 ` [PATCH v3 4/4] btrfs: use IOMAP_DIO_BOUNCE flag instead of falling back to buffered IO Qu Wenruo
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