linux-kernel - Re: [PATCH v2] mm, page_alloc: Fix has_unmovable

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Date:   Tue, 18 Dec 2018 08:36:55 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Oscar Salvador <osalvador@...e.de>, vbabka@...e.cz,
        pavel.tatashin@...rosoft.com, rppt@...ux.vnet.ibm.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm, page_alloc: Fix has_unmovable_pages for HugePages

On Mon 17-12-18 15:07:26, Andrew Morton wrote:
> On Mon, 17 Dec 2018 23:51:13 +0100 Oscar Salvador <osalvador@...e.de> wrote:
> 
> > v1 -> v2:
> > 	- Fix the logic for skipping pages by Michal
> > 
> > ---
> 
> Please be careful with the "^---$".  It signifies end-of-changelog, so
> I ended up without a changelog!
> 
> > >From e346b151037d3c37feb10a981a4d2a25018acf81 Mon Sep 17 00:00:00 2001
> > From: Oscar Salvador <osalvador@...e.de>
> > Date: Mon, 17 Dec 2018 14:53:35 +0100
> > Subject: [PATCH] mm, page_alloc: Fix has_unmovable_pages for HugePages
> > 
> > While playing with gigantic hugepages and memory_hotplug, I triggered
> > the following #PF when "cat memoryX/removable":
> > 
> > ...
> >
> > Also, since gigantic pages span several pageblocks, re-adjust the logic
> > for skipping pages.
> > 
> > Signed-off-by: Oscar Salvador <osalvador@...e.de>

Acked-by: Michal Hocko <mhocko@...e.com>

> cc:stable?

See http://lkml.kernel.org/r/20181217152936.GR30879@dhcp22.suse.cz. I
believe nobody is simply using gigantic pages and hotplug at the same
time and those pages do not seem to cross cma regions as well. At least
not since hugepage_migration_supported stops reporting giga pages as
migrateable.

That being said, I do not think we really need it in stable but it
should be relatively easy to backport so no objection from me to put it
there.

-- 
Michal Hocko
SUSE Labs