On Fri, Nov 22, 2024 at 09:44:16AM -0800, Suren Baghdasaryan wrote: >Add helper functions to speculatively perform operations without >read-locking mmap_lock, expecting that mmap_lock will not be >write-locked and mm is not modified from under us. > >Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> >Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> >Reviewed-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> >--- >Changes since v2 [1] >- Added SOB, per Liam Howlett > >[1] https://lore.kernel.org/all/20241121162826.987947-3-surenb@xxxxxxxxxx/ > > include/linux/mmap_lock.h | 33 +++++++++++++++++++++++++++++++-- > 1 file changed, 31 insertions(+), 2 deletions(-) > >diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h >index 9715326f5a85..8ac3041df053 100644 >--- a/include/linux/mmap_lock.h >+++ b/include/linux/mmap_lock.h >@@ -71,6 +71,7 @@ static inline void mmap_assert_write_locked(const struct mm_struct *mm) > } > > #ifdef CONFIG_PER_VMA_LOCK >+ > static inline void mm_lock_seqcount_init(struct mm_struct *mm) > { > seqcount_init(&mm->mm_lock_seq); >@@ -87,11 +88,39 @@ static inline void mm_lock_seqcount_end(struct mm_struct *mm) > do_raw_write_seqcount_end(&mm->mm_lock_seq); > } > >-#else >+static inline bool mmap_lock_speculate_try_begin(struct mm_struct *mm, unsigned int *seq) >+{ >+ /* >+ * Since mmap_lock is a sleeping lock, and waiting for it to become >+ * unlocked is more or less equivalent with taking it ourselves, don't >+ * bother with the speculative path if mmap_lock is already write-locked >+ * and take the slow path, which takes the lock. >+ */ >+ return raw_seqcount_try_begin(&mm->mm_lock_seq, *seq); >+} >+ >+static inline bool mmap_lock_speculate_retry(struct mm_struct *mm, unsigned int seq) >+{ >+ return do_read_seqcount_retry(&mm->mm_lock_seq, seq); Just curious why we don't use read_seqcount_retry(). Looks this is the only user outside seqlock.h. >+} >+ >+#else /* CONFIG_PER_VMA_LOCK */ >+ > static inline void mm_lock_seqcount_init(struct mm_struct *mm) {} > static inline void mm_lock_seqcount_begin(struct mm_struct *mm) {} > static inline void mm_lock_seqcount_end(struct mm_struct *mm) {} >-#endif >+ >+static inline bool mmap_lock_speculate_try_begin(struct mm_struct *mm, unsigned int *seq) >+{ >+ return false; >+} >+ >+static inline bool mmap_lock_speculate_retry(struct mm_struct *mm, unsigned int seq) >+{ >+ return true; >+} >+ >+#endif /* CONFIG_PER_VMA_LOCK */ > > static inline void mmap_init_lock(struct mm_struct *mm) > { >-- >2.47.0.371.ga323438b13-goog -- Wei Yang Help you, Help me
