Linaro-mm-sig September 2026

linaro-mm-sig@lists.linaro.org

21 participants
51 discussions

Re: [PATCH v8 2/2] dma-buf: Split sgl by largest page-aligned chunk

by Jason Gunthorpe

On Tue, Sep 01, 2026 at 05:08:49PM +0000, David Hu wrote: > From: David Hu <xuehaohu(a)google.com> > > Currently, `fill_sg_entry()` splits the scatterlist using `UINT_MAX`. > This creates a non-page-aligned DMA length (`0xFFFFFFFF`) for the > first entry, resulting in non-page-aligned DMA addresses for all > subsequent entries. This patch is fine, but pedenatically a scatterlist's entry limit should be bounded to dma_get_max_seg_size(), though I don't think it helps this. Operating scatterlists at the size limits has proven problematic in a number of places already... > In addition, a non-page-aligned sgl length will trigger an edge case > in `ib_umem_find_best_pgsz()`. In case of a discontinuity in later > buffers, we will have a `va` with lowest bit set to 1. That will lead > to `ib_umem_find_best_pgsz()` always return 0, and break the promise > to find best page size for the mapping on the NIC side. That's an IB side bug, the newer logic that joins adjacent SGLs should have avoided it? Jason

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Linaro-mm-sig September 2026