RE: [PATCH] zsmalloc: do not use bit_spin_lock

[Song Bao Hua (Barry Song)]

> -----Original Message-----
> From: Song Bao Hua (Barry Song)
> Sent: Tuesday, December 22, 2020 3:03 PM
> To: 'Vitaly Wool' <vitaly.wool@xxxxxxxxxxxx>
> Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>; Minchan Kim <minchan@xxxxxxxxxx>; Mike
> Galbraith <efault@xxxxxx>; LKML <linux-kernel@xxxxxxxxxxxxxxx>; linux-mm
> <linux-mm@xxxxxxxxx>; Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>;
> NitinGupta <ngupta@xxxxxxxxxx>; Sergey Senozhatsky
> <sergey.senozhatsky.work@xxxxxxxxx>; Andrew Morton
> <akpm@xxxxxxxxxxxxxxxxxxxx>; tiantao (H) <tiantao6@xxxxxxxxxxxxx>
> Subject: RE: [PATCH] zsmalloc: do not use bit_spin_lock
> 
> 
> > I'm still not convinced. Will kmap what, src? At this point src might become
> just a bogus pointer.
> 
> As long as the memory is still there, we can kmap it by its page struct. But
> if
> it is not there anymore, we have no way.
> 
> > Why couldn't the object have been moved somewhere else (due to the compaction
> mechanism for instance)
> > at the time DMA kicks in?
> 
> So zs_map_object() will guarantee the src won't be moved by holding those
> preemption-disabled lock?
> If so, it seems we have to drop the MOVABLE gfp in zswap for zsmalloc case?
> 

Or we can do get_page() to avoid the movement of the page.

> >
> > >
> > > ~Vitaly
> >
> 
> Thanks
> Barry