Re: [PATCH 1/2] mem-hotplug: use GFP_HIGHUSER_MOVABLE in, alloc_migrate_target()

[Vlastimil Babka]

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.
> >
> >
> > .