On Mon, Mar 16, 2026 at 09:02:33AM -0700, Breno Leitao wrote: > On Mon, Mar 16, 2026 at 03:44:14PM +0100, David Hildenbrand (Arm) wrote: > > On 3/16/26 14:47, Breno Leitao wrote: > > > On Mon, Mar 16, 2026 at 12:55:13PM +0000, Lorenzo Stoakes (Oracle) wrote: > > >> On Mon, Mar 09, 2026 at 05:00:34AM -0700, Breno Leitao wrote: > > >>> Add a shell-based selftest that exercises the full set of THP sysfs > > >>> knobs: enabled (global and per-size anon), defrag, use_zero_page, > > >>> hpage_pmd_size, shmem_enabled (global and per-size), shrink_underused, > > >>> khugepaged/ tunables, and per-size stats files. > > >>> > > >>> Each writable knob is tested for valid writes, invalid-input rejection, > > >>> idempotent writes, and mode transitions where applicable. All original > > >>> values are saved before testing and restored afterwards. > > >>> > > >>> The test uses the kselftest KTAP framework (ktap_helpers.sh) for > > >>> structured TAP 13 output, making results parseable by the kselftest > > >>> harness. The test plan is printed at the end since the number of test > > >>> points is dynamic (depends on available hugepage sizes and sysfs files). > > >>> > > >>> This is particularly useful for validating the refactoring of > > >>> enabled_store() and anon_enabled_store() to use sysfs_match_string() > > >>> and the new change_enabled()/change_anon_orders() helpers. > > >>> > > >>> Signed-off-by: Breno Leitao <[email protected]> > > >> > > >> The test is broken locally for me, returning error code 127. > > >> > > >> I do appreciate the effort here, so I'm sorry to push back negatively, > > >> but I > > >> feel a bash script here is pretty janky, and frankly if any of these > > >> interfaces > > >> were as broken as this it'd be a major failure that would surely get > > >> picked up > > >> far sooner elsewhere. > > >> > > >> So while I think this might be useful as a local test for your sysfs > > >> interface > > >> changes, I don't think this is really suited to the mm selftests. > > > > > > That is totally fine. This test is what I have been using to test the > > > changes, and I decide to share it in case someone find it useful. > > > > > > Let's drop it. > > > > Out of interest, to we know why the test is failing for Lorenzo? > > I really don't know, but, it sounds like ktap was not found?
Yeah CONFIG_KUNIT is not set so could be :) > > Then the first early-exit path hit: > ktap_skip_all "..." # undefined → returns 127 exit "$KSFT_SKIP" > # expands to: exit "" → exits with last $? = 127 > > > I agree that the test is a bit excessive, in particular when it comes to > > invalid/idempotent values etc. I could see some value for testing > > whether setting the modes keeps working, but also then I wonder if that > > is really something we'll be changing frequently (and that breaks easily). > > yea, I make it very excessive, because there were some intrinsics in > those sysfs that I was gettingit wrong when doing the intial conversion. > > So, the test is something that I trust now, and I found it useful when > finding regressiosn. > > Is is something that will chagne frequently? probably not! > > That said, would you like to have a simplified/different version of this > test? In an ideal world we'd use kunit or something to assert it internal to the kernel I guess, but if we do have something scaled down it'd at least be nice to have in C? :) I am not sure how useful it'd be though overall, I don't see us changing this too often and really we're more interested in asserting behaviour. Sadly THP is inherently tricky to test generally because of its very nature, I wish we could have better test isolation etc. See tools/testing/vma for a forlorn dream of kernel code being run in userland (but oh how the stubs/duplicate declarations/etc. are a pain). I suspect THP could never be given the same treatment though! :) Cheers, Lorenzo
