linux-kernel - Re: [PATCH v7] iomap: make inline data support more flexible

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Message-ID: <YPsbQzcNz+r4V7P2@casper.infradead.org>
Date:   Fri, 23 Jul 2021 20:40:51 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Gao Xiang <hsiangkao@...ux.alibaba.com>
Cc:     linux-erofs@...ts.ozlabs.org, linux-fsdevel@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@....de>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Andreas Gruenbacher <andreas.gruenbacher@...il.com>,
        Huang Jianan <huangjianan@...o.com>
Subject: Re: [PATCH v7] iomap: make inline data support more flexible

On Sat, Jul 24, 2021 at 01:41:31AM +0800, Gao Xiang wrote:
> Add support for reading inline data content into the page cache from
> nonzero page-aligned file offsets.  This enables the EROFS tailpacking
> mode where the last few bytes of the file are stored right after the
> inode.
> 
> The buffered write path remains untouched since EROFS cannot be used
> for testing. It'd be better to be implemented if upcoming real users
> care and provide a real pattern rather than leave untested dead code
> around.

My one complaint with this version is the subject line.  It's a bit vague.
I went with:

iomap: Support file tail packing

I also wrote a changelog entry that reads:
    The existing inline data support only works for cases where the entire
    file is stored as inline data.  For larger files, EROFS stores the
    initial blocks separately and then can pack a small tail adjacent to
    the inode.  Generalise inline data to allow for tail packing.  Tails
    may not cross a page boundary in memory.

... but I'm not sure that's necessarily better than what you've written
here.

> Cc: Christoph Hellwig <hch@....de>
> Cc: Darrick J. Wong <djwong@...nel.org>
> Cc: Matthew Wilcox <willy@...radead.org>
> Cc: Andreas Gruenbacher <andreas.gruenbacher@...il.com>
> Tested-by: Huang Jianan <huangjianan@...o.com> # erofs
> Signed-off-by: Gao Xiang <hsiangkao@...ux.alibaba.com>

Reviewed-by: Matthew Wilcox (Oracle) <willy@...radead.org>