linux-kernel - Re: [PATCH v3 1/7] iov_iter: Introduce fault_in_iov

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Message-ID: <YPtyRgyGqJX4Ya/R@zeniv-ca.linux.org.uk>
Date:   Sat, 24 Jul 2021 01:52:06 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Andreas Gruenbacher <agruenba@...hat.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        "Darrick J. Wong" <djwong@...nel.org>, Jan Kara <jack@...e.cz>,
        Matthew Wilcox <willy@...radead.org>, cluster-devel@...hat.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        ocfs2-devel@....oracle.com
Subject: Re: [PATCH v3 1/7] iov_iter: Introduce fault_in_iov_iter helper

On Fri, Jul 23, 2021 at 10:58:34PM +0200, Andreas Gruenbacher wrote:
> Introduce a new fault_in_iov_iter helper for manually faulting in an iterator.
> Other than fault_in_pages_writeable(), this function is non-destructive.
> 
> We'll use fault_in_iov_iter in gfs2 once we've determined that the iterator
> passed to .read_iter or .write_iter isn't in memory.

Hmm...  I suspect that this is going to be much heavier for read access
than the existing variant.  Do we ever want it for anything other than
writes?