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From: Mike Kravetz <mike.kravetz@oracle.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Michal Hocko <mhocko@suse.com>,
	Shakeel Butt <shakeelb@google.com>,
	Oscar Salvador <osalvador@suse.de>,
	David Hildenbrand <david@redhat.com>,
	Muchun Song <songmuchun@bytedance.com>,
	David Rientjes <rientjes@google.com>,
	Miaohe Lin <linmiaohe@huawei.com>,
	Matthew Wilcox <willy@infradead.org>,
	HORIGUCHI NAOYA <naoya.horiguchi@nec.com>,
	"Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>,
	Waiman Long <longman@redhat.com>, Peter Xu <peterx@redhat.com>,
	Mina Almasry <almasrymina@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Roman Gushchin <guro@fb.com>,
	Christoph Hellwig <hch@infradead.org>
Subject: Re: [RFC PATCH 7/8] hugetlb: add update_and_free_page_no_sleep for irq context
Date: Mon, 22 Mar 2021 10:42:23 -0700	[thread overview]
Message-ID: <2383057a-29dc-383b-720f-7cdcdd015e40@oracle.com> (raw)
In-Reply-To: <YFhYHZ9onwdZMeDi@hirez.programming.kicks-ass.net>

Cc: Roman, Christoph

On 3/22/21 1:41 AM, Peter Zijlstra wrote:
> On Fri, Mar 19, 2021 at 03:42:08PM -0700, Mike Kravetz wrote:
>> The locks acquired in free_huge_page are irq safe.  However, in certain
>> circumstances the routine update_and_free_page could sleep.  Since
>> free_huge_page can be called from any context, it can not sleep.
>>
>> Use a waitqueue to defer freeing of pages if the operation may sleep.  A
>> new routine update_and_free_page_no_sleep provides this functionality
>> and is only called from free_huge_page.
>>
>> Note that any 'pages' sent to the workqueue for deferred freeing have
>> already been removed from the hugetlb subsystem.  What is actually
>> deferred is returning those base pages to the low level allocator.
> 
> So maybe I'm stupid, but why do you need that work in hugetlb? Afaict it
> should be in cma_release().

My thinking (which could be totally wrong) is that cma_release makes no
claims about calling context.  From the code, it is pretty clear that it
can only be called from task context with no locks held.  Although,
there could be code incorrectly calling it today hugetlb does.  Since
hugetlb is the only code with this new requirement, it should do the
work.

Wait!!!  That made me remember something.
Roman had code to create a non-blocking version of cma_release().
https://lore.kernel.org/linux-mm/20201022225308.2927890-1-guro@fb.com/

There were no objections, and Christoph even thought there may be
problems with callers of dma_free_contiguous.

Perhaps, we should just move forward with Roman's patches to create
cma_release_nowait() and avoid this workqueue stuff?
-- 
Mike Kravetz


  reply	other threads:[~2021-03-22 17:43 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-19 22:42 [RFC PATCH 0/8] make hugetlb put_page safe for all calling contexts Mike Kravetz
2021-03-19 22:42 ` [RFC PATCH 1/8] hugetlb: add per-hstate mutex to synchronize user adjustments Mike Kravetz
2021-03-22 13:59   ` Michal Hocko
2021-03-22 16:57     ` Mike Kravetz
2021-03-23  7:48       ` Michal Hocko
2021-03-19 22:42 ` [RFC PATCH 2/8] hugetlb: recompute min_count when dropping hugetlb_lock Mike Kravetz
2021-03-22 14:07   ` Michal Hocko
2021-03-22 23:07     ` Mike Kravetz
2021-03-23  7:50       ` Michal Hocko
2021-03-23  8:01         ` Peter Zijlstra
2021-03-23  8:14           ` Michal Hocko
2021-03-23 23:18             ` Mike Kravetz
2021-03-24  8:36               ` Michal Hocko
2021-03-24 16:43                 ` Mike Kravetz
2021-03-19 22:42 ` [RFC PATCH 3/8] hugetlb: create remove_hugetlb_page() to separate functionality Mike Kravetz
2021-03-22 14:15   ` Michal Hocko
2021-03-22 17:01     ` Mike Kravetz
2021-03-19 22:42 ` [RFC PATCH 4/8] hugetlb: call update_and_free_page without hugetlb_lock Mike Kravetz
2021-03-22 14:19   ` Michal Hocko
2021-03-19 22:42 ` [RFC PATCH 5/8] hugetlb: change free_pool_huge_page to remove_pool_huge_page Mike Kravetz
2021-03-22 14:31   ` Michal Hocko
2021-03-22 23:28     ` Mike Kravetz
2021-03-23  7:57       ` Michal Hocko
2021-03-24  1:03         ` Mike Kravetz
2021-03-24  8:40           ` Michal Hocko
2021-03-24 16:38             ` Mike Kravetz
2021-03-24 16:50               ` Michal Hocko
2021-03-19 22:42 ` [RFC PATCH 6/8] hugetlb: make free_huge_page irq safe Mike Kravetz
2021-03-21 19:55   ` Mike Kravetz
2021-03-22 13:36   ` [hugetlb] cd190f60f9: BUG:sleeping_function_called_from_invalid_context_at_mm/hugetlb.c kernel test robot
2021-03-22 14:35   ` [RFC PATCH 6/8] hugetlb: make free_huge_page irq safe Michal Hocko
2021-03-19 22:42 ` [RFC PATCH 7/8] hugetlb: add update_and_free_page_no_sleep for irq context Mike Kravetz
2021-03-20  1:18   ` Hillf Danton
2021-03-25  0:26     ` Mike Kravetz
2021-03-22  8:41   ` Peter Zijlstra
2021-03-22 17:42     ` Mike Kravetz [this message]
2021-03-22 18:10       ` Roman Gushchin
2021-03-23 18:51         ` Mike Kravetz
2021-03-23 19:07           ` Roman Gushchin
2021-03-24  8:43           ` Michal Hocko
2021-03-24 16:53             ` Mike Kravetz
2021-03-22 20:43       ` Peter Zijlstra
2021-03-22 14:42   ` Michal Hocko
2021-03-22 14:46     ` Michal Hocko
2021-03-19 22:42 ` [RFC PATCH 8/8] hugetlb: track hugetlb pages allocated via cma_alloc Mike Kravetz

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