From: Minchan Kim <minchan@kernel.org>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Minchan Kim <minchan@kernel.org>, Todd Kjos <tkjos@google.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Martijn Coenen <maco@android.com>
Subject: [PATCH v2] ANDROID: binder: change down_write to down_read
Date: Thu, 29 Mar 2018 10:00:40 +0900 [thread overview]
Message-ID: <20180329010040.96760-1-minchan@kernel.org> (raw)
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: Todd Kjos <tkjos@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Martijn Coenen <maco@android.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
>From v1:
* remove WARN_ON_ONCE - Greg
* add reviewed-by - Martijn
Martijn, I took your LGTM of v1 as Reviewed-by. If you don't like it
or want to change it to acked-by, please, tell me.
drivers/android/binder.c | 2 +-
drivers/android/binder_alloc.c | 6 +++---
2 files changed, 4 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..4f382d51def1 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;
}
@@ -288,7 +288,7 @@ 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 +321,7 @@ 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
next reply other threads:[~2018-03-29 1:00 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-29 1:00 Minchan Kim [this message]
2018-03-29 1:59 ` [PATCH v2] ANDROID: binder: change down_write to down_read Arve Hjønnevåg
2018-03-29 2:01 ` Minchan Kim
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