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Date: Tue, 22 Dec 2020 02:10:42 +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 > -----Original Message----- > From: Song Bao Hua (Barry Song) > Sent: Tuesday, December 22, 2020 3:03 PM > 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? > Or we can do get_page() to avoid the movement of the page. > > > > > > > > ~Vitaly > > > > Thanks > Barry
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