On Mon, Aug 23, 2021 at 12:47 PM Gerald Schaefer <gerald.schae...@linux.ibm.com> wrote: > > On Mon, 23 Aug 2021 16:05:46 +0200 > Gerald Schaefer <gerald.schae...@linux.ibm.com> wrote: > > > On Fri, 20 Aug 2021 07:43:40 +0200 > > Christoph Hellwig <h...@lst.de> wrote: > > > > > Hi all, > > > > > > looking at the recent ZONE_DEVICE related changes we still have a > > > horrible maze of different code paths. I already suggested to > > > depend on ARCH_HAS_PTE_SPECIAL for ZONE_DEVICE there, which all modern > > Oh, we do have PTE_SPECIAL, actually that took away the last free bit > in the pte. So, if there is a chance that ZONE_DEVICE would depend > on PTE_SPECIAL instead of PTE_DEVMAP, we might be back in the game > and get rid of that CONFIG_FS_DAX_LIMITED.
So PTE_DEVMAP is primarily there to coordinate the get_user_pages_fast() path, and even there it's usage can be eliminated in favor of PTE_SPECIAL. I started that effort [1], but need to rebase on new notify_failure infrastructure coming from Ruan [2]. So I think you are not in the critical path until I can get the PTE_DEVMAP requirement out of your way. [1]: https://lore.kernel.org/r/161604050866.1463742.7759521510383551055.st...@dwillia2-desk3.amr.corp.intel.com [2]: https://lore.kernel.org/r/20210730085245.3069812-1-ruansy.f...@fujitsu.com
