linux-kernel - Re: [PATCH 2/2] mm/page_owner: set correct gfp_mask on page

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Date:	Mon, 20 Jul 2015 20:54:13 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Joonsoo Kim <js1304@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH 2/2] mm/page_owner: set correct gfp_mask on page_owner

On Mon, Jul 20, 2015 at 01:27:55PM +0200, Vlastimil Babka wrote:
> On 07/16/2015 02:06 AM, Minchan Kim wrote:
> >On Wed, Jul 15, 2015 at 03:33:59PM +0900, Joonsoo Kim wrote:
> >>@@ -2003,7 +2005,7 @@ int __isolate_free_page(struct page *page, unsigned int order)
> >>  	zone->free_area[order].nr_free--;
> >>  	rmv_page_order(page);
> >>
> >>-	set_page_owner(page, order, 0);
> >>+	set_page_owner(page, order, __GFP_MOVABLE);
> >
> >It seems the reason why  __GFP_MOVABLE is okay is that __isolate_free_page
> >works on a free page on MIGRATE_MOVABLE|MIGRATE_CMA's pageblock. But if we
> >break the assumption in future, here is broken again?
> 
> I didn't study the page owner code yet and I'm catching up after
> vacation, but I share your concern. But I don't think the
> correctness depends on the pageblock we are isolating from. I think
> the assumption is that the isolated freepage will be used as a
> target for migration, and that only movable pages can be
> successfully migrated (but also CMA pages, and that information can
> be lost?). However there are also efforts to allow migrate e.g.
> driver pages that won't be marked as movable. And I'm not sure which
> migratetype are balloon pages which already have special migration
> code.

I am one of people who want to migrate driver pages from compaction
from zram point of view so I agree with you.
However, If I make zram support migratepages, I will use __GFP_MOVABLE.
So, I'm not sure there is any special driver that it can support migrate
via migratepage but it doesn't set __GFP_MOVABLE.

Having said that, I support your opinion because __GFP_MOVABLE is not
only gfp mask for allocating so we should take care of complete gfp
mask from original page.


> 
> So what I would think (without knowing all details) that the page
> owner info should be transferred during page migration with all the
> other flags, and shouldn't concern __isolate_free_page() at all?
> 

I agree.
 
Thanks.
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