linux-kernel - Re: [PATCH] iomap: Fix the write_count in iomap_add_to

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Message-ID: <20200822131312.GA17997@infradead.org>
Date:   Sat, 22 Aug 2020 14:13:12 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Dave Chinner <david@...morbit.com>
Cc:     Ritesh Harjani <riteshh@...ux.ibm.com>,
        Anju T Sudhakar <anju@...ux.vnet.ibm.com>, hch@...radead.org,
        darrick.wong@...cle.com, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        willy@...radead.org
Subject: Re: [PATCH] iomap: Fix the write_count in iomap_add_to_ioend().

On Sat, Aug 22, 2020 at 07:53:58AM +1000, Dave Chinner wrote:
> but iomap only allows BIO_MAX_PAGES when creating the bio. And:
> 
> #define BIO_MAX_PAGES 256
> 
> So even on a 64k page machine, we should not be building a bio with
> more than 16MB of data in it. So how are we getting 4GB of data into
> it?

BIO_MAX_PAGES is the number of bio_vecs in the bio, it has no
direct implication on the size, as each entry can fit up to UINT_MAX
bytes.