On Thu, 21 Dec 2023 09:17:55 +0000
David Laight [off-list ref] wrote:

quoted

Unfortunately, it has to be PAGE_SIZE (and for now it's a power of 2 to
make masking easy). It's used for splice and will also be used for memory
mapping with user space.  

Perhaps then the sysctl to set the size should be powers of 4k

It's not a sysctl but a file in tracefs

with a minimum size of PAGE_SIZE.
Then you don't have to know the page size when setting things up.

The user shouldn't need to know either. But the size of the sub-buffer
limits the biggest size of an event, so the user only needs to make sure
the sub-buffer is bigger than their biggest event.

I'm also guessing that no Linux kernels have a PAGE_SIZE of 2k?
IIRC some old mmu (maybe 68020 era) used 2k pages.

I think 1kb units is perfectly fine (patch 15 changes to kb units). The
interface says its to define the minimal size of the sub-buffer, not the
actual size.

-- Steve