linux-kernel - RE: [PATCH 1/2] mm: drop migrate type checks from has_unmovable

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Date:   Mon, 13 Nov 2017 07:33:13 +0000
From:   Ran Wang <ran.wang_1@....com>
To:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Michal Hocko <mhocko@...e.com>
CC:     Michael Ellerman <mpe@...erman.id.au>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        Yasuaki Ishimatsu <yasu.isimatu@...il.com>,
        "qiuxishi@...wei.com" <qiuxishi@...wei.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, Leo Li <leoyang.li@....com>,
        Xiaobo Xie <xiaobo.xie@....com>
Subject: RE: [PATCH 1/2] mm: drop migrate type checks from has_unmovable_pages

Hello Michal,

<snip>

> Date: Fri, 13 Oct 2017 14:00:12 +0200
> 
> From: Michal Hocko <mhocko@...e.com>
> 
> Michael has noticed that the memory offline tries to migrate kernel code
> pages when doing  echo 0 > /sys/devices/system/memory/memory0/online
> 
> The current implementation will fail the operation after several failed page
> migration attempts but we shouldn't even attempt to migrate that memory
> and fail right away because this memory is clearly not migrateable. This will
> become a real problem when we drop the retry loop counter resp. timeout.
> 
> The real problem is in has_unmovable_pages in fact. We should fail if there
> are any non migrateable pages in the area. In orther to guarantee that
> remove the migrate type checks because MIGRATE_MOVABLE is not
> guaranteed to contain only migrateable pages. It is merely a heuristic.
> Similarly MIGRATE_CMA does guarantee that the page allocator doesn't
> allocate any non-migrateable pages from the block but CMA allocations
> themselves are unlikely to migrateable. Therefore remove both checks.
> 
> Reported-by: Michael Ellerman <mpe@...erman.id.au>
> Signed-off-by: Michal Hocko <mhocko@...e.com>
> Tested-by: Michael Ellerman <mpe@...erman.id.au>
> Acked-by: Vlastimil Babka <vbabka@...e.cz>
> ---
>  mm/page_alloc.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c index
> 3badcedf96a7..ad0294ab3e4f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -7355,9 +7355,6 @@ bool has_unmovable_pages(struct zone *zone,
> struct page *page, int count,
>  	 */
>  	if (zone_idx(zone) == ZONE_MOVABLE)
>  		return false;
> -	mt = get_pageblock_migratetype(page);
> -	if (mt == MIGRATE_MOVABLE || is_migrate_cma(mt))
> -		return false;

This drop cause DWC3 USB controller fail on initialization with Layerscaper processors
(such as LS1043A) as below:

[    2.701437] xhci-hcd xhci-hcd.0.auto: new USB bus registered, assigned bus number 1
[    2.710949] cma: cma_alloc: alloc failed, req-size: 1 pages, ret: -16
[    2.717411] xhci-hcd xhci-hcd.0.auto: can't setup: -12
[    2.727940] xhci-hcd xhci-hcd.0.auto: USB bus 1 deregistered
[    2.733607] xhci-hcd: probe of xhci-hcd.0.auto failed with error -12
[    2.739978] xhci-hcd xhci-hcd.1.auto: xHCI Host Controller

And I notice that someone also reported to you that DWC2 got affected recently,
so do you have the solution now?

Best regards

Ran
> 
>  	pfn = page_to_pfn(page);
>  	for (found = 0, iter = 0; iter < pageblock_nr_pages; iter++) {