linux-kernel - RE: [PATCH] zsmalloc: do not use bit_spin

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Date:   Tue, 22 Dec 2020 02:07:53 +0000
From:   "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>
To:     Vitaly Wool <vitaly.wool@...sulko.com>
CC:     Shakeel Butt <shakeelb@...gle.com>,
        Minchan Kim <minchan@...nel.org>,
        "Mike Galbraith" <efault@....de>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        NitinGupta <ngupta@...are.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "tiantao (H)" <tiantao6@...ilicon.com>
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?

> 
> >
> > ~Vitaly
> 

Thanks
Barry