| Message ID | 20250107030415.721474-1-surenb@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [1/1] mm: remove extra check for VMA_LOCK_OFFSET when read-locking a vma | expand |
On Mon, Jan 06, 2025 at 07:04:15PM -0800, Suren Baghdasaryan wrote: >Since we limit vm_refcnt at VMA_REF_LIMIT and it's smaller than >VMA_LOCK_OFFSET, there is no need to check again if VMA_LOCK_OFFSET bit >is set. Remove the extra check and add a clarifying comment. > >Fixes: e8f32ff00a66 ("mm: replace vm_lock and detached flag with a reference count") >Suggested-by: Wei Yang <richard.weiyang@gmail.com> >Signed-off-by: Suren Baghdasaryan <surenb@google.com> Reviewed-by: Wei Yang <richard.weiyang@gmail.com> >--- >Applies over mm-unstable > > include/linux/mm.h | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > >diff --git a/include/linux/mm.h b/include/linux/mm.h >index 486638d22fc6..b5f262fc7dc5 100644 >--- a/include/linux/mm.h >+++ b/include/linux/mm.h >@@ -747,7 +747,11 @@ static inline bool vma_start_read(struct mm_struct *mm, struct vm_area_struct *v > > > rwsem_acquire_read(&vma->vmlock_dep_map, 0, 0, _RET_IP_); >- /* Limit at VMA_REF_LIMIT to leave one count for a writer */ >+ /* >+ * Limit at VMA_REF_LIMIT to leave one count for a writer. >+ * If VMA_LOCK_OFFSET is set, __refcount_inc_not_zero_limited() will fail >+ * because VMA_REF_LIMIT is less than VMA_LOCK_OFFSET. >+ */ > if (unlikely(!__refcount_inc_not_zero_limited(&vma->vm_refcnt, &oldcnt, > VMA_REF_LIMIT))) { > rwsem_release(&vma->vmlock_dep_map, _RET_IP_); >@@ -766,8 +770,7 @@ static inline bool vma_start_read(struct mm_struct *mm, struct vm_area_struct *v > * after it has been unlocked. > * This pairs with RELEASE semantics in vma_end_write_all(). > */ >- if (unlikely(oldcnt & VMA_LOCK_OFFSET || >- vma->vm_lock_seq == raw_read_seqcount(&mm->mm_lock_seq))) { >+ if (unlikely(vma->vm_lock_seq == raw_read_seqcount(&mm->mm_lock_seq))) { > vma_refcount_put(vma); > return false; > } > >base-commit: f349e79bfbf3abfade8011797ff6d0d47b67dab7 >-- >2.47.1.613.gc27f4b7a9f-goog
On Tue, Jan 7, 2025 at 4:28 AM Wei Yang <richard.weiyang@gmail.com> wrote: > > On Mon, Jan 06, 2025 at 07:04:15PM -0800, Suren Baghdasaryan wrote: > >Since we limit vm_refcnt at VMA_REF_LIMIT and it's smaller than > >VMA_LOCK_OFFSET, there is no need to check again if VMA_LOCK_OFFSET bit > >is set. Remove the extra check and add a clarifying comment. > > > >Fixes: e8f32ff00a66 ("mm: replace vm_lock and detached flag with a reference count") > >Suggested-by: Wei Yang <richard.weiyang@gmail.com> > >Signed-off-by: Suren Baghdasaryan <surenb@google.com> > > Reviewed-by: Wei Yang <richard.weiyang@gmail.com> Since I have to respin v8, I'll fold this fix into the original patch. > > >--- > >Applies over mm-unstable > > > > include/linux/mm.h | 9 ++++++--- > > 1 file changed, 6 insertions(+), 3 deletions(-) > > > >diff --git a/include/linux/mm.h b/include/linux/mm.h > >index 486638d22fc6..b5f262fc7dc5 100644 > >--- a/include/linux/mm.h > >+++ b/include/linux/mm.h > >@@ -747,7 +747,11 @@ static inline bool vma_start_read(struct mm_struct *mm, struct vm_area_struct *v > > > > > > rwsem_acquire_read(&vma->vmlock_dep_map, 0, 0, _RET_IP_); > >- /* Limit at VMA_REF_LIMIT to leave one count for a writer */ > >+ /* > >+ * Limit at VMA_REF_LIMIT to leave one count for a writer. > >+ * If VMA_LOCK_OFFSET is set, __refcount_inc_not_zero_limited() will fail > >+ * because VMA_REF_LIMIT is less than VMA_LOCK_OFFSET. > >+ */ > > if (unlikely(!__refcount_inc_not_zero_limited(&vma->vm_refcnt, &oldcnt, > > VMA_REF_LIMIT))) { > > rwsem_release(&vma->vmlock_dep_map, _RET_IP_); > >@@ -766,8 +770,7 @@ static inline bool vma_start_read(struct mm_struct *mm, struct vm_area_struct *v > > * after it has been unlocked. > > * This pairs with RELEASE semantics in vma_end_write_all(). > > */ > >- if (unlikely(oldcnt & VMA_LOCK_OFFSET || > >- vma->vm_lock_seq == raw_read_seqcount(&mm->mm_lock_seq))) { > >+ if (unlikely(vma->vm_lock_seq == raw_read_seqcount(&mm->mm_lock_seq))) { > > vma_refcount_put(vma); > > return false; > > } > > > >base-commit: f349e79bfbf3abfade8011797ff6d0d47b67dab7 > >-- > >2.47.1.613.gc27f4b7a9f-goog > > -- > Wei Yang > Help you, Help me
diff --git a/include/linux/mm.h b/include/linux/mm.h index 486638d22fc6..b5f262fc7dc5 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -747,7 +747,11 @@ static inline bool vma_start_read(struct mm_struct *mm, struct vm_area_struct *v rwsem_acquire_read(&vma->vmlock_dep_map, 0, 0, _RET_IP_); - /* Limit at VMA_REF_LIMIT to leave one count for a writer */ + /* + * Limit at VMA_REF_LIMIT to leave one count for a writer. + * If VMA_LOCK_OFFSET is set, __refcount_inc_not_zero_limited() will fail + * because VMA_REF_LIMIT is less than VMA_LOCK_OFFSET. + */ if (unlikely(!__refcount_inc_not_zero_limited(&vma->vm_refcnt, &oldcnt, VMA_REF_LIMIT))) { rwsem_release(&vma->vmlock_dep_map, _RET_IP_); @@ -766,8 +770,7 @@ static inline bool vma_start_read(struct mm_struct *mm, struct vm_area_struct *v * after it has been unlocked. * This pairs with RELEASE semantics in vma_end_write_all(). */ - if (unlikely(oldcnt & VMA_LOCK_OFFSET || - vma->vm_lock_seq == raw_read_seqcount(&mm->mm_lock_seq))) { + if (unlikely(vma->vm_lock_seq == raw_read_seqcount(&mm->mm_lock_seq))) { vma_refcount_put(vma); return false; }
Since we limit vm_refcnt at VMA_REF_LIMIT and it's smaller than VMA_LOCK_OFFSET, there is no need to check again if VMA_LOCK_OFFSET bit is set. Remove the extra check and add a clarifying comment. Fixes: e8f32ff00a66 ("mm: replace vm_lock and detached flag with a reference count") Suggested-by: Wei Yang <richard.weiyang@gmail.com> Signed-off-by: Suren Baghdasaryan <surenb@google.com> --- Applies over mm-unstable include/linux/mm.h | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) base-commit: f349e79bfbf3abfade8011797ff6d0d47b67dab7