Messages in this thread Patch in this message | | | From | Minchan Kim <> | Subject | [PATCH] ANDROID: binder: change down_write to down_read | Date | Wed, 28 Mar 2018 11:42:31 +0900 |
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binder_update_page_range needs down_write of mmap_sem because vm_insert_page need to change vma->vm_flags to VM_MIXEDMAP unless it is set. However, when I profile binder working, it seems every binder buffers should be mapped in advance by binder_mmap. It means we could set VM_MIXEDMAP in bider_mmap time which is already hold a mmap_sem as down_write so binder_update_page_range doesn't need to hold a mmap_sem as down_write.
Android suffers from mmap_sem contention so let's reduce mmap_sem down_write.
Cc: Martijn Coenen <maco@android.com> Cc: Todd Kjos <tkjos@google.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Minchan Kim <minchan@kernel.org> --- drivers/android/binder.c | 2 +- drivers/android/binder_alloc.c | 8 +++++--- 2 files changed, 6 insertions(+), 4 deletions(-)
diff --git a/drivers/android/binder.c b/drivers/android/binder.c index 764b63a5aade..9a14c6dd60c4 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -4722,7 +4722,7 @@ static int binder_mmap(struct file *filp, struct vm_area_struct *vma) failure_string = "bad vm_flags"; goto err_bad_arg; } - vma->vm_flags = (vma->vm_flags | VM_DONTCOPY) & ~VM_MAYWRITE; + vma->vm_flags |= (VM_DONTCOPY | VM_MIXEDMAP) & ~VM_MAYWRITE; vma->vm_ops = &binder_vm_ops; vma->vm_private_data = proc; diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c index 5a426c877dfb..a184bf12eb15 100644 --- a/drivers/android/binder_alloc.c +++ b/drivers/android/binder_alloc.c @@ -219,7 +219,7 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate, mm = alloc->vma_vm_mm; if (mm) { - down_write(&mm->mmap_sem); + down_read(&mm->mmap_sem); vma = alloc->vma; } @@ -229,6 +229,8 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate, goto err_no_vma; } + WARN_ON_ONCE(vma && !(vma->vm_flags & VM_MIXEDMAP)); + for (page_addr = start; page_addr < end; page_addr += PAGE_SIZE) { int ret; bool on_lru; @@ -288,7 +290,7 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate, /* vm_insert_page does not seem to increment the refcount */ } if (mm) { - up_write(&mm->mmap_sem); + up_read(&mm->mmap_sem); mmput(mm); } return 0; @@ -321,7 +323,7 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate, } err_no_vma: if (mm) { - up_write(&mm->mmap_sem); + up_read(&mm->mmap_sem); mmput(mm); } return vma ? -ENOMEM : -ESRCH; -- 2.17.0.rc1.321.gba9d0f2565-goog
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