Re: regression - mm: shmem: add large folio support for tmpfs affect GPU performance.

[Hugh Dickins <hughd@google.com>]

On Fri, 25 Jul 2025, Baolin Wang wrote:
> > 
> > I hope to correct the logic of i915 driver's shmem allocation, by extending
> > the shmem write length in the i915 driver to allocate PMD- sized THPs. IIUC,
> > some sample fix code is as follows (untested). Patryk, could you help test
> > it to see if this resolves your issue? Thanks.

This patch cannot be the right fix.  It may be a very sensible workaround
for some in-kernel drivers (I've not looked or tried); but unless I
misunderstand, it does nothing to restore userspace behaviour on a
huge=always tmpfs.

Please reread my comment earlier in the thread, in particular,
Passing a new SIGBUS xfstest does not excuse a regression: strict PAGE_SIZE
SIGBUS behaviour is fine for the newly-featured mTHPs or large folios,
but not for the long-established huge=always.

Thanks,
Hugh