linux-kernel - Re: [RFC PATCH 7/8] hugetlb: add update_and_free_page_no

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Date:   Mon, 22 Mar 2021 15:46:25 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Mike Kravetz <mike.kravetz@...cle.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 7/8] hugetlb: add update_and_free_page_no_sleep for
 irq context

On Mon 22-03-21 15:42:27, Michal Hocko wrote:
[...]
> Besides that the changelog doesn't really say anything about changed
> user visible behavior change. Now if somebody decreases the GB huge pool
> from the userspace the real effect on the freed up memory will be
> postponed to some later time. That "later" is unpredictable as it
> depends on WQ utilization. We definitely need some sort of
> wait_for_inflight pages. One way to do that would be to have a dedicated
> WQ and schedule a sync work item after the pool has been shrunk and wait
> for that item.

Scratch that. It is not really clear from the patch context but after
looking at the resulting code set_max_huge_pages will use the blockable
update_and_free_page so we should be fine.

Sorry about the noise!
-- 
Michal Hocko
SUSE Labs