linux-kernel - Re: [RFC PATCH 5/8] hugetlb: change free_pool_huge_page to remove_pool_huge

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Date:   Wed, 24 Mar 2021 09:38:17 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Shakeel Butt <shakeelb@...gle.com>,
        Oscar Salvador <osalvador@...e.de>,
        David Hildenbrand <david@...hat.com>,
        Muchun Song <songmuchun@...edance.com>,
        David Rientjes <rientjes@...gle.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        HORIGUCHI NAOYA <naoya.horiguchi@....com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Waiman Long <longman@...hat.com>, Peter Xu <peterx@...hat.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 5/8] hugetlb: change free_pool_huge_page to
 remove_pool_huge_page

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.
-- 
Mike Kravetz