linux-kernel - Re: [PATCH v11 07/14] HMM: mm add helper to update page table when migrating memory v2.

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Date:	Fri, 23 Oct 2015 11:25:54 +0800
From:	"Hillf Danton" <hillf.zj@...baba-inc.com>
To:	"'Jerome Glisse'" <jglisse@...hat.com>
Cc:	"'linux-kernel'" <linux-kernel@...r.kernel.org>,
	<linux-mm@...ck.org>
Subject: Re: [PATCH v11 07/14] HMM: mm add helper to update page table when migrating memory v2.

> > > This is a multi-stage process, first we save and replace page table
> > > entry with special HMM entry, also flushing tlb in the process. If
> > > we run into non allocated entry we either use the zero page or we
> > > allocate new page. For swaped entry we try to swap them in.
> > >
> > Please elaborate why swap entry is handled this way.
> 
> So first, this is only when you have a device then use HMM and a device
> that use memory migration. So far it only make sense for discrete GPUs.
> So regular workload that do not use a GPUs with HMM are not impacted and
> will not go throught this code path.
> 
> Now, here we are migrating memory because the device driver is asking for
> it, so presumably we are expecting that the device will use that memory
> hence we want to swap in anything that have been swap to disk. Once it is
> swap in memory we copy it to device memory and free the pages. So in the
> end we only need to allocate a page temporarily until we move things to
> the device.
> 
I prefer it is in log message.

thanks
Hillf

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