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

From: Vlastimil Babka
Date: Mon Jul 18 2016 - 04:05:50 EST

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

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

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

Xishi Qiu