On 31.01.23 16:36, Jens Axboe wrote:
Using FOLL_PIN for mapping user pages caused a performance regression of
about 2.7%. Looking at profiles, we see:
+2.71% [kernel.vmlinux] [k] mod_node_page_state
which wasn't there before. The node page state counters are percpu, but
with a very low threshold. On my setup, every 108th update ends up
needing to punt to two atomic_lond_add()'s, which is causing this above
regression.
As these counters are purely for debug purposes, move them under
CONFIG_DEBUG_VM rather than do them unconditionally.
Fixes: fd20d0c1852e ("block: convert bio_map_user_iov to use iov_iter_extract_pages")
Fixes: 920756a3306a ("block: Convert bio_iov_iter_get_pages to use iov_iter_extract_pages")
Link: https://lore.kernel.org/linux-block/f57ee72f-38e9-6afa-182f-2794638eadcb@xxxxxxxxx/
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
I added fixes tags, even though it's not a strict fix for this commits.
But it does fix a performance regression introduced by those commits.
It's a useful hint for backporting.
I'd just mention them in the commit log instead, but I don't
particularly care here as long as the commit ID's are stable.
If still possible, I'd include this as a preparational change for these
commits instead. Anyhow
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
--
Thanks,
David / dhildenb
