Re: [PATCH v2 1/2] nvme-pci: Use size_t for length fields to handle larger sizes

Leon Romanovsky
2025-11-19T09:55:22Z

On Tue, Nov 18, 2025 at 06:03:11AM +0100, Christoph Hellwig wrote:
> On Mon, Nov 17, 2025 at 09:22:43PM +0200, Leon Romanovsky wrote:
> > From: Leon Romanovsky <leonro@nvidia.com>
> >
> > This patch changes the length variables from unsigned int to size_t.
> > Using size_t ensures that we can handle larger sizes, as size_t is
> > always equal to or larger than the previously used u32 type.
> >
> > Originally, u32 was used because blk-mq-dma code evolved from
> > scatter-gather implementation, which uses unsigned int to describe length.
> > This change will also allow us to reuse the existing struct phys_vec in places
> > that don't need scatter-gather.
> >
> > Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
> > Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
> > ---
> > block/blk-mq-dma.c | 8 ++++++--
> > drivers/nvme/host/pci.c | 4 ++--
> > 2 files changed, 8 insertions(+), 4 deletions(-)
> >
> > diff --git a/block/blk-mq-dma.c b/block/blk-mq-dma.c
> > index e9108ccaf4b0..e7d9b54c3eed 100644
> > --- a/block/blk-mq-dma.c
> > +++ b/block/blk-mq-dma.c
> > @@ -8,7 +8,7 @@
> >
> > struct phys_vec {
> > phys_addr_t paddr;
> > - u32 len;
> > + size_t len;
> > };
>
> So we're now going to increase memory usage by 50% again after just
> reducing it by removing the scatterlist?

It is slightly less.

Before this change: 96 bits
After this change (on 64bits system): 128 bits.

It is 33% increase per-structure.

So what is the resolution? Should I drop this patch or not?

Thanks