Re: [PATCH v4 04/11] mm/hugetlb: make hugetlb migration callback CMA aware

From: Mike Kravetz <mike.kravetz@oracle.com>
To: Joonsoo Kim <js1304@gmail.com>, Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	kernel-team@lge.com, Christoph Hellwig <hch@infradead.org>,
	Roman Gushchin <guro@fb.com>,
	Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
	Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH v4 04/11] mm/hugetlb: make hugetlb migration callback CMA aware
Date: Wed, 8 Jul 2020 17:27:22 -0700	[thread overview]
Message-ID: <d170cede-7972-7c95-0666-e2743a1c70cd@oracle.com> (raw)
In-Reply-To: <20200708071602.GB16543@js1304-desktop>

On 7/8/20 12:16 AM, Joonsoo Kim wrote:
> On Tue, Jul 07, 2020 at 01:22:31PM +0200, Vlastimil Babka wrote:
>> On 7/7/20 9:44 AM, js1304@gmail.com wrote:
>>> From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
>>>
<...>
>>> This patch makes the deque function on hugetlb CMA aware and skip CMA
>>> pages if newly added skip_cma argument is passed as true.
>>
>> Hmm, can't you instead change dequeue_huge_page_node_exact() to test the PF_
>> flag and avoid adding bool skip_cma everywhere?
> 
> Okay! Please check following patch.
>>
>> I think that's what Michal suggested [1] except he said "the code already does
>> by memalloc_nocma_{save,restore} API". It needs extending a bit though, AFAICS.
>> __gup_longterm_locked() indeed does the save/restore, but restore comes before
>> check_and_migrate_cma_pages() and thus new_non_cma_page() is called, so an
>> adjustment is needed there, but that's all?
>>
>> Hm the adjustment should be also done because save/restore is done around
>> __get_user_pages_locked(), but check_and_migrate_cma_pages() also calls
>> __get_user_pages_locked(), and that call not being between nocma save and
>> restore is thus also a correctness issue?
> 
> Simply, I call memalloc_nocma_{save,restore} in new_non_cma_page(). It
> would not cause any problem.
> 
> ------------------>8-------------------
> From bcfc57e3c6f2df1ad2940308b89d740cd3f0fba8 Mon Sep 17 00:00:00 2001
> From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Date: Wed, 8 Jul 2020 14:39:26 +0900
> Subject: [PATCH] mm/hugetlb: make hugetlb migration callback CMA aware
> 
<...>
> 
> This patch makes new_non_cma_page() uses memalloc_nocma_{save,restore}
> to exclude CMA memory rather than manually clearing __GFP_MOVABLE. And,
> this patch also makes the deque function on hugetlb CMA aware. In the
> deque function, CMA memory is skipped if PF_MEMALLOC_NOCMA flag is set
> by memalloc_nocma_{save,restore}.
> 
> Acked-by: Mike Kravetz <mike.kravetz@oracle.com>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>

I did ACK the previous version of the patch, but I like this much better.
I assume there will be a new version built on top of Michal's patch to
change the placement of memalloc_nocma_restore calls in __gup_longterm_locked.

-- 
Mike Kravetz