Re: [PATCH 5/7] iomap: limit buffered I/O size to 128M

["Darrick J. Wong" <djwong@kernel.org>]

On Mon, Feb 03, 2025 at 10:43:09AM +0100, Christoph Hellwig wrote:
> Currently iomap can build extremely large bios (I've seen sizes
> up to 480MB).  Limit this to a lower bound so that the soon to
> be added per-ioend integrity buffer doesn't go beyond what the
> page allocator can support.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/iomap/buffered-io.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 06990e012884..71bb676d4998 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -456,6 +456,7 @@ static loff_t iomap_readpage_iter(const struct iomap_iter *iter,
>  	sector = iomap_sector(iomap, pos);
>  	if (!ctx->bio ||
>  	    bio_end_sector(ctx->bio) != sector ||
> +	    ctx->bio->bi_iter.bi_size > SZ_128M ||

I imagine this is one of the XXX parts, but we probably shouldn't limit
the bios for !pi filesystems that won't care.

--D

>  	    !bio_add_folio(ctx->bio, folio, plen, poff)) {
>  		if (ctx->bio)
>  			iomap_read_submit_bio(iter, ctx);
> @@ -1674,6 +1675,8 @@ static struct iomap_ioend *iomap_alloc_ioend(struct iomap_writepage_ctx *wpc,
>  static bool iomap_can_add_to_ioend(struct iomap_writepage_ctx *wpc, loff_t pos,
>  		u16 ioend_flags)
>  {
> +	if (wpc->ioend->io_bio.bi_iter.bi_size > SZ_128M)
> +		return false;
>  	if (ioend_flags & IOMAP_IOEND_BOUNDARY)
>  		return false;
>  	if ((ioend_flags & IOMAP_IOEND_NOMERGE_FLAGS) !=
> -- 
> 2.45.2
> 
>