linux-kernel - Re: [PATCH 1/2] mem-hotplug: use GFP_HIGHUSER_MOVABLE in, alloc_migrate

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Message-ID: <7ce4a7ac-07aa-6a81-48c2-91c4a9355778@suse.cz>
Date:	Mon, 18 Jul 2016 10:05:44 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Xishi Qiu <qiuxishi@...wei.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] mem-hotplug: use GFP_HIGHUSER_MOVABLE in,
 alloc_migrate_target()

On 07/18/2016 10:00 AM, Xishi Qiu wrote:
> On 2016/7/18 13:51, Joonsoo Kim wrote:
>
>> On Fri, Jul 15, 2016 at 10:47:06AM +0800, Xishi Qiu wrote:
>>> alloc_migrate_target() is called from migrate_pages(), and the page
>>> is always from user space, so we can add __GFP_HIGHMEM directly.
>>
>> No, all migratable pages are not from user space. For example,
>> blockdev file cache has __GFP_MOVABLE and migratable but it has no
>> __GFP_HIGHMEM and __GFP_USER.
>>
>
> Hi Joonsoo,
>
> So the original code "gfp_t gfp_mask = GFP_USER | __GFP_MOVABLE;"
> is not correct?

It's not incorrect. GFP_USER just specifies some reclaim flags, and may 
perhaps restrict allocation through __GFP_HARDWALL, where the original
page could have been allocated without the restriction. But it doesn't 
put the place in an unexpected address range, as placing a non-highmem 
page into highmem could. __GFP_MOVABLE then just controls a heuristic 
for placement within a zone.

>> And, zram's memory isn't GFP_HIGHUSER_MOVABLE but has __GFP_MOVABLE.
>>
>
> Can we distinguish __GFP_MOVABLE or GFP_HIGHUSER_MOVABLE when doing
> mem-hotplug?

I don't understand the question here, can you rephrase with more detail? 
Thanks.

> Thanks,
> Xishi Qiu
>
>> Thanks.
>>
>>
>> .
>>
>
>
>