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

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Message-ID: <CAHpGcMJThSqjowuEGCzjNFN8y5tq8kxmxfSivwtuTEMK_xd-cQ@mail.gmail.com>
Date:   Sat, 24 Jul 2021 10:05:17 +0200
From:   Andreas Grünbacher <andreas.gruenbacher@...il.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Andreas Gruenbacher <agruenba@...hat.com>,
        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 <cluster-devel@...hat.com>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ocfs2-devel@....oracle.com
Subject: Re: [PATCH v3 1/7] iov_iter: Introduce fault_in_iov_iter helper

Am Sa., 24. Juli 2021 um 03:53 Uhr schrieb Al Viro <viro@...iv.linux.org.uk>:
> 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?

I don't know if it actually is slower when pages need to be faulted
in, but I'm fine turning it into a write-only function.

Thanks,
Andreas