On 27.01.25 17:56, Matthew Wilcox wrote:
On Mon, Jan 27, 2025 at 05:20:25PM +0100, David Hildenbrand wrote:
14.04% postgres [kernel.kallsyms] [k] try_grab_folio_fast
|
--14.04%--try_grab_folio_fast
gup_fast_fallback
|
--13.85%--iov_iter_extract_pages
bio_iov_iter_get_pages
iomap_dio_bio_iter
__iomap_dio_rw
iomap_dio_rw
xfs_file_dio_read
xfs_file_read_iter
__io_read
io_read
io_issue_sqe
io_submit_sqes
__do_sys_io_uring_enter
do_syscall_64
BTW, two things that come to mind:
(1) We always fallback to GUP-slow, I wonder why. GUP-fast would go via
try_grab_folio_fast().
I don't think we do?
iov_iter_extract_pages() calls
iov_iter_extract_user_pages() calls
pin_user_pages_fast() calls
gup_fast_fallback() calls
gup_fast() calls
gup_fast_pgd_range() calls
gup_fast_p4d_range() calls
gup_fast_pud_range() calls
gup_fast_pud_leaf() calls
try_grab_folio_fast() which is where we see the contention.
If that were to fail, we'd see contention in __get_user_pages_locked(),
right?
Sorry, my brain stripped the "_fast" in the callchain above :( -- it
*is* try_grab_folio_fast() :)
So yes, we are in GUP-fast as one would expect.
--
Cheers,
David / dhildenb
