linux-kernel - Re: [PATCH] mm, hugetlb: use memory policy when available

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Date:	Thu, 5 Nov 2015 14:47:21 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Dave Hansen <dave@...1.net>
Cc:	akpm@...ux-foundation.org, n-horiguchi@...jp.nec.com,
	mike.kravetz@...cle.com, hillf.zj@...baba-inc.com,
	rientjes@...gle.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, dave.hansen@...ux.intel.com
Subject: Re: [PATCH] mm, hugetlb: use memory policy when available

On 10/20/2015 09:53 PM, Dave Hansen wrote:
> From: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> I have a hugetlbfs user which is never explicitly allocating huge pages
> with 'nr_hugepages'.  They only set 'nr_overcommit_hugepages' and then let
> the pages be allocated from the buddy allocator at fault time.
> 
> This works, but they noticed that mbind() was not doing them any good and
> the pages were being allocated without respect for the policy they
> specified.
> 
> The code in question is this:
> 
>> struct page *alloc_huge_page(struct vm_area_struct *vma,
> ...
>>         page = dequeue_huge_page_vma(h, vma, addr, avoid_reserve, gbl_chg);
>>         if (!page) {
>>                 page = alloc_buddy_huge_page(h, NUMA_NO_NODE);
> 
> dequeue_huge_page_vma() is smart and will respect the VMA's memory policy.
> But, it only grabs _existing_ huge pages from the huge page pool.  If the
> pool is empty, we fall back to alloc_buddy_huge_page() which obviously
> can't do anything with the VMA's policy because it isn't even passed the
> VMA.
> 
> Almost everybody preallocates huge pages.  That's probably why nobody has
> ever noticed this.  Looking back at the git history, I don't think this
> _ever_ worked from when alloc_buddy_huge_page() was introduced in 7893d1d5,
> 8 years ago.
> 
> The fix is to pass vma/addr down in to the places where we actually call in
> to the buddy allocator.  It's fairly straightforward plumbing.  This has
> been lightly tested.
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> Cc: Mike Kravetz <mike.kravetz@...cle.com>
> Cc: Hillf Danton <hillf.zj@...baba-inc.com>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>

Together with the fix and NUMA=n cleanup

Acked=by: Vlastimil Babka <vbabka@...e.cz>

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