On 16.08.23 16:13, Daniel Gomez wrote:
On Wed, Aug 16, 2023 at 08:04:11PM +0800, Yin, Fengwei wrote:
On 8/16/2023 7:44 PM, Daniel Gomez wrote:
On Wed, Aug 16, 2023 at 07:30:35AM +0800, Yin Fengwei wrote:
On 8/15/23 21:25, Daniel Gomez wrote:
Hi Yin,
On Tue, Aug 08, 2023 at 10:09:17AM +0800, Yin Fengwei wrote:
Commit 98b211d6415f ("madvise: convert madvise_free_pte_range() to use a
folio") replaced the page_mapcount() with folio_mapcount() to check
whether the folio is shared by other mapping.
It's not correct for large folios. folio_mapcount() returns the total
mapcount of large folio which is not suitable to detect whether the folio
is shared.
Use folio_estimated_sharers() which returns a estimated number of shares.
That means it's not 100% correct. It should be OK for madvise case here.
I'm trying to understand why it should be ok for madvise this change, so
I hope it's okay to ask you few questions.
folio_mapcount() calculates the total maps for all the subpages of a
folio. However, the folio_estimated_sharers does it only for the first
subpage making it not true for large folios. Then, wouldn't this change
drop support for large folios?
I saw David explained this very well in another mail.
Seems like folio_entire_mapcount() is not accurate either because of it
does not inclue PTE-mapped sub-pages which I think we need here. Hence,
the folio_mapcount(). Could this be something missing in the test side?
I tried to replicate the setup with CONFIG_TRANSPARENT_HUGEPAGE but
seems like I'm not able to do it:
./cow
# [INFO] detected THP size: 2048 KiB
# [INFO] detected hugetlb size: 2048 KiB
# [INFO] detected hugetlb size: 1048576 KiB
# [INFO] huge zeropage is enabled
TAP version 13
1..166
# [INFO] Anonymous memory tests in private mappings
# [RUN] Basic COW after fork() ... with base page
not ok 1 MADV_NOHUGEPAGE failed
# [RUN] Basic COW after fork() ... with swapped out base page
not ok 2 MADV_NOHUGEPAGE failed
# [RUN] Basic COW after fork() ... with THP
not ok 3 MADV_HUGEPAGE failed
# [RUN] Basic COW after fork() ... with swapped-out THP
not ok 4 MADV_HUGEPAGE failed
# [RUN] Basic COW after fork() ... with PTE-mapped THP
not ok 5 MADV_HUGEPAGE failed
# [RUN] Basic COW after fork() ... with swapped-out, PTE-mapped THP
not ok 6 MADV_HUGEPAGE failed
...
Can you post the MADV_PAGEOUT and PTE-mapped THP related testing result?
And I suppose swap need be enabled also for the testing.
You may find a dump of the logs in the link below with system information. Let me
know if you find something wrong in my setup or if you need something else.
Besides CONFIG_TRANSPARENT_HUGEPAGE, CONFIG_SWAP is also enabled in the kernel.
https://gitlab.com/-/snippets/2584135
Also, strace reports ENOSYS for MADV_*:
madvise(0x7f2912465000, 4096, MADV_NOHUGEPAGE) = -1 ENOSYS (Function not implemented)
madvise(0x7f2912000000, 2097152, MADV_HUGEPAGE) = -1 ENOSYS (Function not implemented)
O. The problem here is MADV_HUGEPAGE/MADV_NOHUGEPAGE doesn't work.
Do you have CONFIG_ADVISE_SYSCALLS enabled?
It worked after I enabled the conf. Some tests failed and some were
skipped. But I managed to reproduce the issue now, thanks Yin!
Bail out! 4 out of 166 tests failed
# Totals: pass:146 fail:4 xfail:0 xpass:0 skip:16 error:0
These hugetlb that are failing are known failures.
--
Cheers,
David / dhildenb
