On 16 Apr 2026, at 4:47, David Hildenbrand (Arm) wrote: > On 4/15/26 20:01, Zi Yan wrote: >> On 15 Apr 2026, at 5:21, Baolin Wang wrote: >> >>> On 4/15/26 4:00 PM, David Hildenbrand (Arm) wrote: >>> >>> My comments are in reply to Zi’s comment: >>> >>> "I think hugepage_global_enabled() should be enough to decide whether >>> khugepaged should run or not. " >>> >>> I’m concerned that only relying on hugepage_global_enabled() to decide >>> whether khugepaged should run would cause a regression for anonymous and >>> shmem memory collapse, as it ignores per-size mTHP configuration. >>> >>>> The question is really which semantics we want. >>>> >>>> Right now, there is no way to disable khugepaged for anon pages, to just >>>> get them during page faults. >>> >>> Right. >>> >>>> And we are now talking about the same problem for FS: to only get them >>>> during page faults (like we did so far without >>>> CONFIG_READ_ONLY_THP_FOR_FS). >>> >>> OK. I’m fine with using hugepage_global_enabled() to determine whether >>> khugepaged scans file folios. >>> >>> My concern is that for anonymous memory and shmem, the per-size mTHP >>> settings should be considered. >> >> OK, I misunderstood the meaning of hugepage_global_enabled(), since per-size >> mTHP settings could also enable khugepaged if PMD_SIZE is set. >> >> I will take willy’s original suggestion and make khugepaged on if the global >> setting is enabled. The below is the new version of this patch. I moved anon >> pmd huge page code to a separate anon_hpage_pmd_enabled() like >> shmem_hpage_pmd_enabled() and cleaned up the comment. Let me know your >> thoughts. >> >> Thanks. >> >> From 92b92f2b2ab41c70b41dd304ce648786ee6a1603 Mon Sep 17 00:00:00 2001 >> From: Zi Yan <[email protected]> >> Date: Wed, 15 Apr 2026 13:52:50 -0400 >> Subject: [PATCH] mm/khugepaged: remove READ_ONLY_THP_FOR_FS check in >> hugepage_pmd_enabled() >> >> Remove READ_ONLY_THP_FOR_FS and khugepaged for file-backed pmd-sized >> hugepages are enabled by the global transparent hugepage control. >> khugepaged can still be enabled by per-size control for anon and shmem when >> the global control is off. >> >> Signed-off-by: Zi Yan <[email protected]> >> --- >> mm/khugepaged.c | 26 +++++++++++++++----------- >> 1 file changed, 15 insertions(+), 11 deletions(-) >> >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index b8452dbdb043..586d27ce896e 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -406,18 +406,8 @@ static inline int collapse_test_exit_or_disable(struct >> mm_struct *mm) >> mm_flags_test(MMF_DISABLE_THP_COMPLETELY, mm); >> } >> >> -static bool hugepage_pmd_enabled(void) >> +static inline bool anon_hpage_pmd_enabled() >> { >> - /* >> - * We cover the anon, shmem and the file-backed case here; file-backed >> - * hugepages, when configured in, are determined by the global control. >> - * Anon pmd-sized hugepages are determined by the pmd-size control. >> - * Shmem pmd-sized hugepages are also determined by its pmd-size >> control, >> - * except when the global shmem_huge is set to SHMEM_HUGE_DENY. >> - */ >> - if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && >> - hugepage_global_enabled()) >> - return true; >> if (test_bit(PMD_ORDER, &huge_anon_orders_always)) >> return true; >> if (test_bit(PMD_ORDER, &huge_anon_orders_madvise)) >> @@ -425,6 +415,20 @@ static bool hugepage_pmd_enabled(void) >> if (test_bit(PMD_ORDER, &huge_anon_orders_inherit) && >> hugepage_global_enabled()) >> return true; >> + return false; >> +} >> + > > Works for me. > >> +static bool hugepage_pmd_enabled(void) >> +{ >> + /* >> + * Anon, shmem and file-backed pmd-sized hugepages are all determined by >> + * the global control. If the global control is off, anon and shmem >> + * pmd-sized hugepages are also determined by its per-size control. >> + */ >> + if (hugepage_global_enabled()) >> + return true; >> + if (anon_hpage_pmd_enabled()) >> + return true; >> if (IS_ENABLED(CONFIG_SHMEM) && shmem_hpage_pmd_enabled()) > > BTW, can we please provide a stub for shmem_hpage_pmd_enabled() in > shmem_fs.h such that we can remove the IS_ENABLED here? >
Sure. Best Regards, Yan, Zi
