Re: [PATCH mmotm 5/5] huge tmpfs: add shmem_pmd_fault()

From: Stephen Rothwell
Date: Wed Apr 20 2016 - 19:56:39 EST

Hi Hugh,

On Sat, 16 Apr 2016 16:41:33 -0700 (PDT) Hugh Dickins <hughd@xxxxxxxxxx> wrote:
> The pmd_fault() method gives the filesystem an opportunity to place
> a trans huge pmd entry at *pmd, before any pagetable is exposed (and
> an opportunity to split it on COW fault): now use it for huge tmpfs.
> This patch is a little raw: with more time before LSF/MM, I would
> probably want to dress it up better - the shmem_mapping() calls look
> a bit ugly; it's odd to want FAULT_FLAG_MAY_HUGE and VM_FAULT_HUGE just
> for a private conversation between shmem_fault() and shmem_pmd_fault();
> and there might be a better distribution of work between those two, but
> prising apart that series of huge tests is not to be done in a hurry.
> Good for now, presents the new way, but might be improved later.
> This patch still leaves the huge tmpfs map_team_by_pmd() allocating a
> pagetable while holding page lock, but other filesystems are no longer
> doing so; and we've not yet settled whether huge tmpfs should (like anon
> THP) or should not (like DAX) participate in deposit/withdraw protocol.
> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
> ---
> I've been testing with this applied on top of mmotm plus 1-4/5,
> but I suppose the right place for it is immediately after
> huge-tmpfs-map-shmem-by-huge-page-pmd-or-by-page-team-ptes.patch
> with a view to perhaps merging it into that in the future.
> mm/huge_memory.c | 4 ++--
> mm/memory.c | 13 +++++++++----
> mm/shmem.c | 33 +++++++++++++++++++++++++++++++++
> 3 files changed, 44 insertions(+), 6 deletions(-)

I added this to the end of mmotm in linux-next today.

Stephen Rothwell