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mm: introduce mmap_lock_speculate_{try_begin|retry}

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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: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Link: https://lkml.kernel.org/r/20241122174416.1367052-3-surenb@google.com
This commit is contained in:
Suren Baghdasaryan 2024-11-22 09:44:16 -08:00 committed by Peter Zijlstra
parent eb449bd969
commit 03a001b156
1 changed files with 31 additions and 2 deletions
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33
include/linux/mmap_lock.h
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@ -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 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_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)
{