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From: Oscar Salvador <osalvador@suse.de>
To: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Michal Hocko <mhocko@kernel.org>,
	akpm@linux-foundation.org, david@redhat.com,
	anthony.yznaga@oracle.com, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm,memory_hotplug: Explicitly pass the head to isolate_huge_page
Date: Wed, 13 Feb 2019 09:13:14 +0100
Message-ID: <20190213081310.zfxwb3svoqsxnuyc@d104.suse.de> (raw)
In-Reply-To: <52f7a47c-4a8b-c06d-04c0-48d9bb43823b@oracle.com>

On Tue, Feb 12, 2019 at 04:13:05PM -0800, Mike Kravetz wrote:
> Well, commit 94310cbcaa3c ("mm/madvise: enable (soft|hard) offline of
> HugeTLB pages at PGD level") should have allowed migration of gigantic
> pages.  I believe it was added for 16GB pages on powerpc.  However, due
> to subsequent changes I suspsect this no longer works.

I will take a look, I am definitely interested in that.
Thanks for pointing it out Mike.

> 
> > This check doesn't make much sense in principle. Why should we bail out
> > based on a section size? We are offlining a pfn range. All that we care
> > about is whether the hugetlb is migrateable.
> 
> Yes.  Do note that the do_migrate_range is only called from __offline_pages
> with a start_pfn that was returned by scan_movable_pages.  scan_movable_pages
> has the hugepage_migration_supported check for PageHuge pages.  So, it would
> seem to be redundant to do another check in do_migrate_range.

Well, the thing is that if the gigantic page does not start at the very beginning
of the memblock, and we do find migrateable pages before it in scan_movable_pages(),
the range that we will pass to do_migrate_ranges() will contain the gigantic page.
So we need the check there to cover that case too, although I agree that the current
check is misleading.

I will think about it.

-- 
Oscar Salvador
SUSE L3


  reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-08  9:06 Oscar Salvador
2019-02-11  8:58 ` David Hildenbrand
2019-02-12  8:33 ` Michal Hocko
2019-02-12 13:45   ` Oscar Salvador
2019-02-12 14:40     ` Michal Hocko
2019-02-13  0:13       ` Mike Kravetz
2019-02-13  8:13         ` Oscar Salvador [this message]
2019-02-13 12:33           ` Michal Hocko
2019-02-13 15:15             ` Oscar Salvador

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