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Date:   Wed, 24 Mar 2021 17:50:24 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     Mike Kravetz <mike.kravetz@oracle.com>
Cc:     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>,
        Peter Zijlstra <peterz@infradead.org>,
        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>
Subject: Re: [RFC PATCH 5/8] hugetlb: change free_pool_huge_page to
 remove_pool_huge_page
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On Wed 24-03-21 09:38:17, Mike Kravetz wrote:
> On 3/24/21 1:40 AM, Michal Hocko wrote:
> > On Tue 23-03-21 18:03:07, Mike Kravetz wrote:
> > [...]
> >> Since you brought up cgroups ... what is your opinion on lock hold time
> >> in hugetlb_cgroup_css_offline?  We could potentially be calling
> >> hugetlb_cgroup_move_parent for every hugetlb page while holding the lock
> >> with interrupts disabled.
> > 
> > I am not familiar with hugetlb cgroup code TBH. But from a quick look
> > there is not much of heavy lifting there. If we find out that this is
> > really visible we can do the lock dance with cond_resched and retry with
> > the iteration again. Or is there any strong reason to process the list
> > in a single go?
> 
> AFAICT, the primary reason for processing the list in a single go is
> that the lock protects the list.  If you drop the lock, the list can
> change ...
> 
> I have come up with a (not so pretty) way of processing the list in
> batches of pages.  But, I dod not want to introduce that if there is no
> need.  Perhaps just take a wait and see approach for now.
> 
> I'll see if I can come up with some timing information to determine
> if/when we may have an issue.

I wouldn't bother at this stage. This can be done on top.
-- 
Michal Hocko
SUSE Labs