Re: [PATCH v10 01/19] zram: sleepable entry locking

[Sebastian Andrzej Siewior]

On 2026-07-07 17:15:21 [+0900], Sergey Senozhatsky wrote:
> On (26/07/07 08:40), Sebastian Andrzej Siewior wrote:
> [..]
> > >  static void zram_slot_lock(struct zram *zram, u32 index)
> > >  {
> > > -	spin_lock(&zram->table[index].lock);
> > > +	unsigned long *lock = &zram->table[index].flags;
> > > +
> > > +	mutex_acquire(slot_dep_map(zram, index), 0, 0, _RET_IP_);
> > > +	wait_on_bit_lock(lock, ZRAM_ENTRY_LOCK, TASK_UNINTERRUPTIBLE);
> > > +	lock_acquired(slot_dep_map(zram, index), _RET_IP_);
> > >  }
> > 
> > Looking at this, is there a special need to have a lockdep map per
> > table? Wouldn't it be enough to have one per zram? Logically you use the
> > same __key so I don't think it makes much of a difference but you could
> > lower the memory usage a bit by having less of those structs per zram.
> 
> So the idea was to separate lockdep maps and keep them per-device
> because various zram devices can be on different IO paths with very
> different locking graphs.  E.g. zram0 can be a swap device with all
> the locks that swap layer has, while zram1 can be a "normal" block
> device mounted with ext4 with all the locks that ext4/vfs bring.

Ach so index will be 0 for zram0 and 1 for zram1? In that case it is
different from what I assumed. But you use the same key so I think it
will be the same lock from lockdep's point of view. Like it will
complain if you do
	zram_slot_lock(zram, 0);
	zram_slot_lock(zram, 1);

without nesting.

Sebastian