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Date:   Tue, 24 Jan 2023 16:08:20 +0000
From:   Matthew Wilcox <willy@infradead.org>
To:     Christoph Hellwig <hch@infradead.org>
Cc:     Qu Wenruo <quwenruo.btrfs@gmx.com>,
        Keith Busch <kbusch@kernel.org>,
        "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>
Subject: Re: What would happen if the block device driver/firmware found some
 block of a bio is corrupted?
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On Mon, Jan 23, 2023 at 10:32:06PM -0800, Christoph Hellwig wrote:
> On Tue, Jan 24, 2023 at 01:38:41PM +0800, Qu Wenruo wrote:
> > The retry for file read is indeed triggered inside VFS, not fs/block/dm
> > layer itself.
> 
> Well, it's really MM code.  If ->readahead fails, we eventually fall
> back to a single-page ->radpage.  That might still be more than one
> sector in some cases, but at least nicely narrows down the range.

I had code to split a large folio into single-page folios at one point,
but I don't believe that ever got merged.  At least, I can't find any
trace of it in filemap.c or iomap/buffered_io.c.  So I think we just
retry the ->read_folio() call each time.