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?
Hi Kirill, Ping. Any comment? Thanks, Yang
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.Fixes: 7635d9cbe832 ("mm, thp, proc: report THP eligibility for each vma") Cc: Michal Hocko <[email protected]> Cc: Vlastimil Babka <[email protected]> Cc: David Rientjes <[email protected]> Cc: Kirill A. Shutemov <[email protected]> Signed-off-by: Yang Shi <[email protected]> --- 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
