On Sun, Nov 24, 2024 at 4:58 PM Wei Yang <richard.weiyang@xxxxxxxxx> wrote: > > 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. Ah, good eye! read_seqcount_retry() would be better. Peter, do you want me to post a new patchset or you can patch it when picking it up? > > >+} > >+ > >+#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
