Re: [PATCH net-next v2 2/4] udmabuf: emit one sg entry per pinned folio

[Bobby Eshleman <bobbyeshleman@gmail.com>]

On Tue, Jun 16, 2026 at 01:57:49PM -0700, Bobby Eshleman wrote:
> On Tue, Jun 16, 2026 at 06:04:03AM +0000, Kasireddy, Vivek wrote:
> > Adding Jason to this discussion.
> > 
> > Hi Bobby,
> > 
> > > Subject: [PATCH net-next v2 2/4] udmabuf: emit one sg entry per pinned
> > > folio
> > > 
> > > From: Bobby Eshleman <bobbyeshleman@meta.com>
> > > 
> > > get_sg_table() emitted one PAGE_SIZE sg entry per page even when the
> > > underlying folio was larger.
> > > 
> > > Instead, walk folios[] and emit one sg entry per folio. When folios
> > We have recently merged a patch (that will make it into 7.2) from Jason that
> > replaced sg_set_folio() with sg_alloc_table_from_pages() in udmabuf driver:
> > https://gitlab.freedesktop.org/drm/tip/-/commit/5bf888673e0dda5a53220fa0c4956271a46c353c
> > 
> > Since you are relying on sg_set_folio(), the core argument against its usage
> > in udmabuf is that it doesn't work well with offsets > PAGE_SIZE, resulting
> > in a malformed scatterlist. Not sure if this can be fixed easily.
> > 
> > > represent large pages (as is for MFD_HUGETLB), each sg entry is a large
> > > page. Normal PAGE_SIZE sg tables are unchanged.
> > > 
> > > This is helpful for importers like net/core/devmem that expect dmabuf sg
> > IMO, udmabuf needs to detect whether importers can handle segments that
> > are > PAGE_SIZE and set the entries appropriately. Please look into how the
> > GPU drivers and other dmabuf exporters/importers handle this situation, so
> > that we can adopt best practices to address this issue.
> > 
> > Thanks,
> > Vivek
> 
> Hey Vivek,
> 
> It sounds looks like that patch might solve my problem. I'll apply and
> troubleshoot from there.
> 
> Thanks!
> 
> Best,
> Bobby

Good news for me, that patch solves the problem. Thanks for bringing
that up! I can drop my udmabuf patch when I respin the series.

Best,
Bobby