linux-kernel - Re: [PATCH v2 15/30] xfs: Define usercopy region in xfs

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Date:   Tue, 29 Aug 2017 05:45:36 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Dave Chinner <david@...morbit.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org, David Windsor <dave@...lcore.net>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        linux-xfs@...r.kernel.org, linux-mm@...ck.org,
        kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v2 15/30] xfs: Define usercopy region in xfs_inode slab
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On Tue, Aug 29, 2017 at 10:31:26PM +1000, Dave Chinner wrote:
> Probably should.  I've already been looking at killing the inline
> extents array to simplify the management of the extent list (much
> simpler to index by rbtree when we don't have direct/indirect
> structures), so killing the inline data would get rid of the other
> part of the union the inline data sits in.

That's exactly where I came form with my extent list work.  Although
the rbtree performance was horrible due to the memory overhead and
I've switched to a modified b+tree at the moment..

> OTOH, if we're going to have to dynamically allocate the memory for
> the extent/inline data for the data fork, it may just be easier to
> make the entire data fork a dynamic allocation (like the attr fork).

I though about this a bit, but it turned out that we basically
always need the data anyway, so I don't think it's going to buy
us much unless we shrink the inode enough so that they better fit
into a page.