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Subject: Re: [PATCH v2] mm/hugetlb: defer free_huge_page() to a workqueue
To:     Andrew Morton <akpm@linux-foundation.org>,
        Waiman Long <longman@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Michal Hocko <mhocko@kernel.org>, aneesh.kumar@linux.ibm.com
References: <20191211194615.18502-1-longman@redhat.com>
 <4fbc39a9-2c9c-4c2c-2b13-a548afe6083c@oracle.com>
 <32d2d4f2-83b9-2e40-05e2-71cd07e01b80@redhat.com>
 <0fcce71f-bc20-0ea3-b075-46592c8d533d@oracle.com>
 <20191212060650.ftqq27ftutxpc5hq@linux-p48b>
 <20191212063050.ufrpij6s6jkv7g7j@linux-p48b>
 <20191212190427.ouyohviijf5inhur@linux-p48b>
From:   Mike Kravetz <mike.kravetz@oracle.com>
Message-ID: <d6b9743c-776c-d740-73af-a600f15b910a@oracle.com>
Date:   Thu, 12 Dec 2019 11:22:55 -0800
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On 12/12/19 11:04 AM, Davidlohr Bueso wrote:
> There have been deadlock reports[1, 2] where put_page is called
> from softirq context and this causes trouble with the hugetlb_lock,
> as well as potentially the subpool lock.
> 
> For such an unlikely scenario, lets not add irq dancing overhead
> to the lock+unlock operations, which could incur in expensive
> instruction dependencies, particularly when considering hard-irq
> safety. For example PUSHF+POPF on x86.
> 
> Instead, just use a workqueue and do the free_huge_page() in regular
> task context.
> 
> [1] https://lore.kernel.org/lkml/20191211194615.18502-1-longman@redhat.com/
> [2] https://lore.kernel.org/lkml/20180905112341.21355-1-aneesh.kumar@linux.ibm.com/
> 
> Reported-by: Waiman Long <longman@redhat.com>
> Reported-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> Signed-off-by: Davidlohr Bueso <dbueso@suse.de>

Thank you Davidlohr.

The patch does seem fairly simple and straight forward.  I need to brush up
on my workqueue knowledge to provide a full review.

Longman,
Do you have a test to reproduce the issue?  If so, can you try running with
this patch.
-- 
Mike Kravetz