linux-kernel - Re: [PATCH 1/2] iomap: support tail packing inline read

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Message-ID: <YPVfxn6/oCPBZpKu@infradead.org>
Date:   Mon, 19 Jul 2021 12:19:34 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Andreas Gr?nbacher <andreas.gruenbacher@...il.com>,
        Christoph Hellwig <hch@...radead.org>,
        linux-erofs@...ts.ozlabs.org,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Darrick J. Wong" <djwong@...nel.org>, Chao Yu <chao@...nel.org>,
        Liu Bo <bo.liu@...ux.alibaba.com>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        Liu Jiang <gerry@...ux.alibaba.com>
Subject: Re: [PATCH 1/2] iomap: support tail packing inline read

On Sat, Jul 17, 2021 at 07:40:41PM +0100, Matthew Wilcox wrote:
> Well, either sense of a WARN_ON is wrong.
> 
> For a file which is PAGE_SIZE + 3 bytes in size, to_iomap_page() will
> be NULL.  For a file which is PAGE_SIZE/2 + 3 bytes in size,
> to_iomap_page() will not be NULL.  (assuming the block size is <=
> PAGE_SIZE / 2).
> 
> I think we need a prep patch that looks something like this:

Something like this is where we should eventually end up, but it
also affects the read from disk case so we need to be careful.