On Wed, Mar 05, 2025 at 06:11:24PM +0000, Matthew Wilcox wrote:

On Wed, Mar 05, 2025 at 12:43:02PM +0100, Hannes Reinecke wrote:

quoted

Oh, sure. But what annoys me: why do we have to care?

When doing I/O _all_ data is stuffed into bvecs via
bio_add_page(), and after that information about the
origin is lost; any iteration on the bio will be a bvec
iteration.
Previously we could just do a bvec iteration, get a reference
for each page, and start processing.
Now suddenly the caller has to check if it's a slab page and don't
get a reference for that. Not only that, he also has to remember
to _not_ drop the reference when he's done.
And, of course, tracing get_page() and the corresponding put_page()
calls through all the layers.

Networking needs to follow block's lead and STOP GETTING REFCOUNTS ON
PAGES.  That will speed up networking (eliminates two atomic operations per
page).  And of course, it will eliminate this hack in the MM.  I think
we do need to put this hack into the MM for now, but it needs to go away
again as quickly as possible.

What worries me is that nobody in networking has replied to this thread
yet.  Do they not care?  Let's see if a subject line change will help
with that.

Since it triggered a kernel crash, I am pretty sure people care. How
about sending out a patch to get more attentions?

I am not sure what patterns here you are suggesting to change w.r.t page
refcount, but at least using AI copilot or whatever automation tool should
be very handy.

Thanks.