From: Michal Hocko <mhocko@suse.com>
To: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Roman Gushchin <guro@fb.com>,
Peter Zijlstra <peterz@infradead.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
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>,
Christoph Hellwig <hch@infradead.org>
Subject: Re: [RFC PATCH 7/8] hugetlb: add update_and_free_page_no_sleep for irq context
Date: Wed, 24 Mar 2021 09:43:35 +0100 [thread overview]
Message-ID: <YFr7t1a+gEvLPuAw@dhcp22.suse.cz> (raw)
In-Reply-To: <8a28c691-1e7c-1463-9d59-da31a2926adc@oracle.com>
On Tue 23-03-21 11:51:04, Mike Kravetz wrote:
> On 3/22/21 11:10 AM, Roman Gushchin wrote:
> > On Mon, Mar 22, 2021 at 10:42:23AM -0700, Mike Kravetz wrote:
> >> 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?
> >
> > Sounds good to me. If it's the preferred path, I can rebase and resend
> > those patches (they been carried for some time by Zi Yan for his 1GB THP work,
> > but they are completely independent).
>
> Thanks Roman,
>
> Yes, this is the preferred path. If there is a non blocking version of
> cma_release, then it makes fixup of hugetlb put_page path much easier.
I do not object to the plan I just want to point out that the sparse
vmemmap for hugetlb pages will need to recognize sleep/nosleep variants
of the freeing path as well to handle its vmemmap repopulate games.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2021-03-24 8:44 UTC|newest]
Thread overview: 44+ 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
2021-03-22 8:41 ` Peter Zijlstra
2021-03-22 17:42 ` Mike Kravetz
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 [this message]
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
[not found] ` <20210320011857.2004-1-hdanton@sina.com>
2021-03-25 0:26 ` [RFC PATCH 7/8] hugetlb: add update_and_free_page_no_sleep for irq context Mike Kravetz
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