On Fri, Dec 20, 2024 at 07:32:52PM +0100, David Hildenbrand wrote:

On 19.12.24 00:11, Alistair Popple wrote:

quoted

On Tue, Dec 17, 2024 at 11:31:25PM +0100, David Hildenbrand wrote:

quoted

On 17.12.24 06:13, Alistair Popple wrote:

quoted

The procfs mmu files such as smaps currently ignore device dax and fs
dax pages because these pages are considered special. To maintain
existing behaviour once these pages are treated as normal pages and
returned from vm_normal_page() add tests to explicitly skip them.

Signed-off-by: Alistair Popple <apopple@nvidia.com>
---
   fs/proc/task_mmu.c | 18 ++++++++++++++----
   1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 38a5a3e..c9b227a 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c

@@ -801,6 +801,8 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
   	if (pte_present(ptent)) {
   		page = vm_normal_page(vma, addr, ptent);
+		if (page && (is_device_dax_page(page) || is_fsdax_page(page)))

This "is_device_dax_page(page) || is_fsdax_page(page)" is a common theme
here, likely we should have a special helper?

Sounds good, will add is_dax_page() if there are enough callers left after any
review comments.

:)

In the end there was only a single caller so I will leave this open-coded.

quoted

quoted

But, don't we actually want to include them in the smaps output now? I think
we want.

I'm not an expert in what callers of vm_normal_page() think of as a "normal"
page.

Yeah, it's tricky. It means "this is abnormal, don't look at the struct
page". We're moving away from that, such that these folios/pages will be ...
mostly normal :)

quoted

So my philosphy here was to ensure anything calling vm_normal_page()
didn't accidentally start seeing DAX pages, either by checking existing filters
(lots of callers already call vma_is_special_huge() or some equivalent) or
explicitly filtering them out in the hope someone smarter than me could tell me
it was unneccssary.

That stategy seems to have worked, and so I agree we likely do want them in
smaps. I just didn't want to silently do it without this kind of discussion
first.

Yes, absolutely.

quoted

quoted

The rmap code will indicate these pages in /proc/meminfo, per-node info, in
the memcg ... as "Mapped:" etc.

So likely we just want to also indicate them here, or is there any downsides
we know of?

I don't know of any, and I think it makes sense to also indicate them so will
drop this check in the respin.

It will be easy to hide them later, at least we talked about it. Thanks for
doing all this!

Not a problem. The other main thing in this patch is also hiding them from
/proc/<PID>/pagemap. Based on this discussion I can't think of any good reason
why we would want to hide them there so will also remove the checks in the
pagemap walker.

-- 
Cheers,

David / dhildenb