[PATCH v4 tip/perf/core 2/4] mm: Introduce mmap_lock_speculation_{begin|end}
From: Andrii Nakryiko <andrii@kernel.org>
Date: 2024-10-28 01:09:12
Also in:
bpf, linux-mm, lkml
Subsystem:
memory mapping - locking, the rest · Maintainers:
Andrew Morton, Suren Baghdasaryan, Liam R. Howlett, Lorenzo Stoakes, Linus Torvalds
From: Suren Baghdasaryan <surenb@google.com> 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@infradead.org> Signed-off-by: Suren Baghdasaryan <surenb@google.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> --- include/linux/mmap_lock.h | 29 +++++++++++++++++++++++++++-- 1 file changed, 27 insertions(+), 2 deletions(-)
diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
index 6b3272686860..58dde2e35f7e 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);
@@ -86,11 +87,35 @@ 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_speculation_begin(struct mm_struct *mm, unsigned int *seq) +{ + *seq = raw_read_seqcount(&mm->mm_lock_seq); + /* Allow speculation if mmap_lock is not write-locked */ + return (*seq & 1) == 0; +} + +static inline bool mmap_lock_speculation_end(struct mm_struct *mm, unsigned int seq) +{ + return !do_read_seqcount_retry(&mm->mm_lock_seq, seq); +} + +#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_speculation_begin(struct mm_struct *mm, unsigned int *seq) +{ + return false; +} + +static inline bool mmap_lock_speculation_end(struct mm_struct *mm, unsigned int seq) +{ + return false; +} + +#endif /* CONFIG_PER_VMA_LOCK */ static inline void mmap_init_lock(struct mm_struct *mm) {
--
2.43.5