Use per-vma locking for concurrent page installations, this minimizes
contention with unrelated vmas improving performance. The mmap_lock is
still acquired when needed though, e.g. before folio_walk_start().
Many thanks to Barry Song who posted a similar approach [1].
Link: https://lore.kernel.org/all/20240902225009.34576-1-21cnbao@gmail.com/ [1]
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Barry Song <v-songbaohua@oppo.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Carlos Llamas <cmllamas@google.com>
---
drivers/android/binder_alloc.c | 70 +++++++++++++++++++++++++++++-----
1 file changed, 60 insertions(+), 10 deletions(-)
diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index d505ffddb6db..47cf1c354e6f 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -234,13 +234,63 @@ static inline bool binder_alloc_is_mapped(struct binder_alloc *alloc)
return smp_load_acquire(&alloc->mapped);
}
+static struct vm_area_struct *binder_find_lock_vma(struct binder_alloc *alloc,
+ unsigned long addr,
+ bool *mm_locked)
+{
+ struct mm_struct *mm = alloc->mm;
+ struct vm_area_struct *vma;
+
+ /* attempt per-vma lock first */
+ vma = lock_vma_under_rcu(mm, addr);
+ if (vma) {
+ *mm_locked = false;
+ return vma;
+ }
+
+ /* fallback to mmap_lock */
+ mmap_read_lock(mm);
+ vma = vma_lookup(mm, addr);
+ if (!vma || !binder_alloc_is_mapped(alloc)) {
+ mmap_read_unlock(mm);
+ return NULL;
+ }
+ *mm_locked = true;
+
+ return vma;
+}
+
+static struct page *binder_page_lookup(struct mm_struct *mm,
+ struct vm_area_struct *vma,
+ unsigned long addr,
+ bool mm_locked)
+{
+ struct folio_walk fw;
+ struct page *page;
+
+ /* folio_walk_start() requires the mmap_lock */
+ if (!mm_locked)
+ mmap_read_lock(mm);
+
+ if (!folio_walk_start(&fw, vma, addr, 0))
+ return NULL;
+
+ page = fw.page;
+ folio_walk_end(&fw, vma);
+
+ if (!mm_locked)
+ mmap_read_unlock(mm);
+
+ return page;
+}
+
static int binder_install_single_page(struct binder_alloc *alloc,
unsigned long index,
unsigned long addr)
{
struct vm_area_struct *vma;
- struct folio_walk fw;
struct page *page;
+ bool mm_locked;
int ret = 0;
if (!mmget_not_zero(alloc->mm))
@@ -257,12 +307,11 @@ static int binder_install_single_page(struct binder_alloc *alloc,
INIT_LIST_HEAD(&page->lru);
page->index = index;
- mmap_read_lock(alloc->mm);
- vma = vma_lookup(alloc->mm, addr);
- if (!vma || !binder_alloc_is_mapped(alloc)) {
+ vma = binder_find_lock_vma(alloc, addr, &mm_locked);
+ if (!vma) {
pr_err("%d: %s failed, no vma\n", alloc->pid, __func__);
ret = -ESRCH;
- goto unlock;
+ goto out;
}
ret = vm_insert_page(vma, addr, page);
@@ -275,14 +324,13 @@ static int binder_install_single_page(struct binder_alloc *alloc,
*/
ret = 0;
__free_page(page);
- if (!folio_walk_start(&fw, vma, addr, 0)) {
+ page = binder_page_lookup(alloc->mm, vma, addr, mm_locked);
+ if (!page) {
pr_err("%d: failed to find page at offset %lx\n",
alloc->pid, addr - alloc->vm_start);
ret = -ESRCH;
break;
}
- page = fw.page;
- folio_walk_end(&fw, vma);
fallthrough;
case 0:
/* Mark page installation complete and safe to use */
@@ -296,8 +344,10 @@ static int binder_install_single_page(struct binder_alloc *alloc,
break;
}
-unlock:
- mmap_read_unlock(alloc->mm);
+ if (mm_locked)
+ mmap_read_unlock(alloc->mm);
+ else
+ vma_end_read(vma);
if (page)
__free_page(page);
out:
--
2.47.0.199.ga7371fff76-googOn Tue, 5 Nov 2024 20:02:50 +0000 Carlos Llamas <cmllamas@google.com>
> Use per-vma locking for concurrent page installations, this minimizes
> contention with unrelated vmas improving performance. The mmap_lock is
> still acquired when needed though, e.g. before folio_walk_start().
>
Is the locking order correct in this patch?
lock vma
lock vma->vm_mm
> Many thanks to Barry Song who posted a similar approach [1].
>
> Link: https://lore.kernel.org/all/20240902225009.34576-1-21cnbao@gmail.com/ [1]
> Cc: Nhat Pham <nphamcs@gmail.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Barry Song <v-songbaohua@oppo.com>
> Cc: Suren Baghdasaryan <surenb@google.com>
> Signed-off-by: Carlos Llamas <cmllamas@google.com>
> ---
> drivers/android/binder_alloc.c | 70 +++++++++++++++++++++++++++++-----
> 1 file changed, 60 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
> index d505ffddb6db..47cf1c354e6f 100644
> --- a/drivers/android/binder_alloc.c
> +++ b/drivers/android/binder_alloc.c
> @@ -234,13 +234,63 @@ static inline bool binder_alloc_is_mapped(struct binder_alloc *alloc)
> return smp_load_acquire(&alloc->mapped);
> }
>
> +static struct vm_area_struct *binder_find_lock_vma(struct binder_alloc *alloc,
> + unsigned long addr,
> + bool *mm_locked)
> +{
> + struct mm_struct *mm = alloc->mm;
> + struct vm_area_struct *vma;
> +
> + /* attempt per-vma lock first */
> + vma = lock_vma_under_rcu(mm, addr);
> + if (vma) {
> + *mm_locked = false;
> + return vma;
> + }
> +
> + /* fallback to mmap_lock */
> + mmap_read_lock(mm);
> + vma = vma_lookup(mm, addr);
> + if (!vma || !binder_alloc_is_mapped(alloc)) {
> + mmap_read_unlock(mm);
> + return NULL;
> + }
> + *mm_locked = true;
> +
> + return vma;
> +}
> +
> +static struct page *binder_page_lookup(struct mm_struct *mm,
> + struct vm_area_struct *vma,
> + unsigned long addr,
> + bool mm_locked)
> +{
> + struct folio_walk fw;
> + struct page *page;
> +
> + /* folio_walk_start() requires the mmap_lock */
> + if (!mm_locked)
> + mmap_read_lock(mm);
> +
> + if (!folio_walk_start(&fw, vma, addr, 0))
> + return NULL;
> +
> + page = fw.page;
> + folio_walk_end(&fw, vma);
> +
> + if (!mm_locked)
> + mmap_read_unlock(mm);
> +
> + return page;
> +}
> +
> static int binder_install_single_page(struct binder_alloc *alloc,
> unsigned long index,
> unsigned long addr)
> {
> struct vm_area_struct *vma;
> - struct folio_walk fw;
> struct page *page;
> + bool mm_locked;
> int ret = 0;
>
> if (!mmget_not_zero(alloc->mm))
> @@ -257,12 +307,11 @@ static int binder_install_single_page(struct binder_alloc *alloc,
> INIT_LIST_HEAD(&page->lru);
> page->index = index;
>
> - mmap_read_lock(alloc->mm);
> - vma = vma_lookup(alloc->mm, addr);
> - if (!vma || !binder_alloc_is_mapped(alloc)) {
> + vma = binder_find_lock_vma(alloc, addr, &mm_locked);
> + if (!vma) {
> pr_err("%d: %s failed, no vma\n", alloc->pid, __func__);
> ret = -ESRCH;
> - goto unlock;
> + goto out;
> }
>
> ret = vm_insert_page(vma, addr, page);
> @@ -275,14 +324,13 @@ static int binder_install_single_page(struct binder_alloc *alloc,
> */
> ret = 0;
> __free_page(page);
> - if (!folio_walk_start(&fw, vma, addr, 0)) {
> + page = binder_page_lookup(alloc->mm, vma, addr, mm_locked);
> + if (!page) {
> pr_err("%d: failed to find page at offset %lx\n",
> alloc->pid, addr - alloc->vm_start);
> ret = -ESRCH;
> break;
> }
> - page = fw.page;
> - folio_walk_end(&fw, vma);
> fallthrough;
> case 0:
> /* Mark page installation complete and safe to use */
> @@ -296,8 +344,10 @@ static int binder_install_single_page(struct binder_alloc *alloc,
> break;
> }
>
> -unlock:
> - mmap_read_unlock(alloc->mm);
> + if (mm_locked)
> + mmap_read_unlock(alloc->mm);
> + else
> + vma_end_read(vma);
> if (page)
> __free_page(page);
> out:
> --
> 2.47.0.199.ga7371fff76-goog
On Thu, Nov 07, 2024 at 06:55:34AM +0800, Hillf Danton wrote: > On Tue, 5 Nov 2024 20:02:50 +0000 Carlos Llamas <cmllamas@google.com> > > Use per-vma locking for concurrent page installations, this minimizes > > contention with unrelated vmas improving performance. The mmap_lock is > > still acquired when needed though, e.g. before folio_walk_start(). > > > Is the locking order correct in this patch? > > lock vma > lock vma->vm_mm Sorry, I've also fixed this issue in v2. I was trying to avoid having to vma_lookup() again after switching locks. However, this seems unavoidable so I've fixed the locking order and I've also switched to get_user_pages_remote(). This seems like a better option now. -- Carlos Llamas
On Tue, Nov 05, 2024 at 08:02:50PM +0000, Carlos Llamas wrote:
> +static struct page *binder_page_lookup(struct mm_struct *mm,
> + struct vm_area_struct *vma,
> + unsigned long addr,
> + bool mm_locked)
> +{
> + struct folio_walk fw;
> + struct page *page;
> +
> + /* folio_walk_start() requires the mmap_lock */
> + if (!mm_locked)
> + mmap_read_lock(mm);
> +
> + if (!folio_walk_start(&fw, vma, addr, 0))
> + return NULL;
Just realized that mmap_lock need to be released if folio_walk_start()
fails and !mm_locked. I'll add the fix for v2.
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