Messages in this thread | | | Subject | Re: [v2 PATCH] mm: thp: fix false negative of shmem vma's THP eligibility | From | Yang Shi <> | Date | Tue, 23 Apr 2019 11:34:13 -0700 |
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On 4/23/19 10:52 AM, Michal Hocko wrote: > On Wed 24-04-19 00:43:01, Yang Shi wrote: >> The commit 7635d9cbe832 ("mm, thp, proc: report THP eligibility for each >> vma") introduced THPeligible bit for processes' smaps. But, when checking >> the eligibility for shmem vma, __transparent_hugepage_enabled() is >> called to override the result from shmem_huge_enabled(). It may result >> in the anonymous vma's THP flag override shmem's. For example, running a >> simple test which create THP for shmem, but with anonymous THP disabled, >> when reading the process's smaps, it may show: >> >> 7fc92ec00000-7fc92f000000 rw-s 00000000 00:14 27764 /dev/shm/test >> Size: 4096 kB >> ... >> [snip] >> ... >> ShmemPmdMapped: 4096 kB >> ... >> [snip] >> ... >> THPeligible: 0 >> >> And, /proc/meminfo does show THP allocated and PMD mapped too: >> >> ShmemHugePages: 4096 kB >> ShmemPmdMapped: 4096 kB >> >> This doesn't make too much sense. The anonymous THP flag should not >> intervene shmem THP. Calling shmem_huge_enabled() with checking >> MMF_DISABLE_THP sounds good enough. And, we could skip stack and >> dax vma check since we already checked if the vma is shmem already. > Kirill, can we get a confirmation that this is really intended behavior > rather than an omission please? Is this documented? What is a global > knob to simply disable THP system wise? > > I have to say that the THP tuning API is one giant mess :/ > > Btw. this patch also seem to fix khugepaged behavior because it previously > ignored both VM_NOHUGEPAGE and MMF_DISABLE_THP.
Aha, I didn't notice this. It looks we need separate the patch to fix that khugepaged problem for both 5.1-rc and LTS.
> >> Fixes: 7635d9cbe832 ("mm, thp, proc: report THP eligibility for each vma") >> Cc: Michal Hocko <mhocko@suse.com> >> Cc: Vlastimil Babka <vbabka@suse.cz> >> Cc: David Rientjes <rientjes@google.com> >> Cc: Kirill A. Shutemov <kirill@shutemov.name> >> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> >> --- >> v2: Check VM_NOHUGEPAGE per Michal Hocko >> >> mm/huge_memory.c | 4 ++-- >> mm/shmem.c | 3 +++ >> 2 files changed, 5 insertions(+), 2 deletions(-) >> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index 165ea46..5881e82 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -67,8 +67,8 @@ bool transparent_hugepage_enabled(struct vm_area_struct *vma) >> { >> if (vma_is_anonymous(vma)) >> return __transparent_hugepage_enabled(vma); >> - if (vma_is_shmem(vma) && shmem_huge_enabled(vma)) >> - return __transparent_hugepage_enabled(vma); >> + if (vma_is_shmem(vma)) >> + return shmem_huge_enabled(vma); >> >> return false; >> } >> diff --git a/mm/shmem.c b/mm/shmem.c >> index 2275a0f..6f09a31 100644 >> --- a/mm/shmem.c >> +++ b/mm/shmem.c >> @@ -3873,6 +3873,9 @@ bool shmem_huge_enabled(struct vm_area_struct *vma) >> loff_t i_size; >> pgoff_t off; >> >> + if ((vma->vm_flags & VM_NOHUGEPAGE) || >> + test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags)) >> + return false; >> if (shmem_huge == SHMEM_HUGE_FORCE) >> return true; >> if (shmem_huge == SHMEM_HUGE_DENY) >> -- >> 1.8.3.1 >>
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