linux-kernel - Re: [PATCH] lib/iov_iter.c: extract virt-contiguous pages in iov_iter_extract_bvec

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Message-ID: <3855842.1728061012@warthog.procyon.org.uk>
Date: Fri, 04 Oct 2024 17:56:52 +0100
From: David Howells <dhowells@...hat.com>
To: Ming Lei <ming.lei@...hat.com>
Cc: dhowells@...hat.com, Jens Axboe <axboe@...nel.dk>,
    Alexander Viro <viro@...iv.linux.org.uk>,
    linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lib/iov_iter.c: extract virt-contiguous pages in iov_iter_extract_bvec_pages

Ming Lei <ming.lei@...hat.com> wrote:

> All iov_iter_bvec() users only want to extract virt-contiguous pages from
> iov_iter_extract_pages() instead physical-contiguous pages.

What do you mean by "virt-contiguous"?  Virtual according to what mapping?

The reason for physical contiguity is that you can pass a set of physical
contiguous pages as a single DMA descriptor.  Therefore, at some point, you
might end up screwing up skb_splice_from_iter().  Currently, that's limited to
a PAGE_SIZE per fragment, but hopefully that will be fixed at some point.

David