linux-kernel - Re: [External] Re: [PATCH 4/6] mm: hugetlb: add return -EAGAIN for dissolve_free_huge

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Date:   Tue, 5 Jan 2021 16:07:48 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Andi Kleen <ak@...ux.intel.com>, mhocko@...e.cz,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [External] Re: [PATCH 4/6] mm: hugetlb: add return -EAGAIN for
 dissolve_free_huge_page

On 1/4/21 7:46 PM, Muchun Song wrote:
> On Tue, Jan 5, 2021 at 11:14 AM Muchun Song <songmuchun@...edance.com> wrote:
>>
>> On Tue, Jan 5, 2021 at 9:33 AM Mike Kravetz <mike.kravetz@...cle.com> wrote:
>>>
>>> On 1/3/21 10:58 PM, Muchun Song wrote:
>>>> When dissolve_free_huge_page() races with __free_huge_page(), we can
>>>> do a retry. Because the race window is small.
>>>
>>> In general, I agree that the race window is small.  However, worst case
>>> would be if the freeing of the page is put on a work queue.  Is it acceptable
>>> to keep retrying in that case?  In addition, the 'Free some vmemmap' series
>>> may slow the free_huge_page path even more.
>>
>> I also consider the 'Free some vmemmap' series case. In my next
>> version series, I will flush the work before dissolve_free_huge_page
>> returns when encountering this race. So the retry is acceptable.
>> Right?
> 
> Hi Mike,
> 
> How about flushing the @free_hpage_work when
> encountering this race?

Flushing should be fine.

The more I think about it, the more I think spinning to retry is not
going to be an issue.  Why?  As you mentioned the race window is quite
small.  It just makes me a bit nervous to retry in a tight loop.
-- 
Mike Kravetz