Re: [PATCH v4 01/10] mmap locking API: initial implementation as rwsem wrappers

From: Davidlohr Bueso
Date: Mon Apr 20 2020 - 15:51:46 EST


On Tue, 14 Apr 2020, Michel Lespinasse wrote:

This change wraps the existing mmap_sem related rwsem calls into a new
mmap locking API. There are two justifications for the new API:

- At first, it provides an easy hooking point to instrument mmap_sem
locking latencies independently of any other rwsems.

- In the future, it may be a starting point for replacing the rwsem
implementation with a different one, such as range locks.

Signed-off-by: Michel Lespinasse <walken@xxxxxxxxxx>
Reviewed-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>

Reviewed-by: Davidlohr Bueso <dbueso@xxxxxxx>

With one observation below.

+static inline void mmap_downgrade_write_lock(struct mm_struct *mm)
+{
+ downgrade_write(&mm->mmap_sem);
+}

Shouldn't this really be just mmap_downgrade_write()? In locking
normally don't add the _lock at the end as it implies the operation
of acquiring the lock.

Thanks,
Davidlohr