linux-kernel - Re: [RFC PATCH] mm: thp: grab the lock before manipulation defer list

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Date:   Tue, 7 Jan 2020 10:33:57 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Wei Yang <richardw.yang@...ux.intel.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>, vdavydov.dev@...il.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        cgroups@...r.kernel.org, linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Yang Shi <yang.shi@...ux.alibaba.com>
Subject: Re: [RFC PATCH] mm: thp: grab the lock before manipulation defer list

On Mon, Jan 06, 2020 at 06:07:29PM -0800, David Rientjes wrote:
>On Tue, 7 Jan 2020, Wei Yang wrote:
>
>> >One thing you might want to do is pull the "if (compound)" check out
>> >and place it outside of the spinlock check. It would then simplify
>> >this signficantly so it is something like
>> >if (compound) {
>> >  spin_lock();
>> >  list = page_deferred_list(page);
>> >  if (!list_empty(list)) {
>> >    list_del_init(list);
>> >    from->..split_queue_len--;
>> >  }
>> >  spin_unlock();
>> >}
>> >
>> >Same for the block below. I would pull the check for compound outside
>> >of the spinlock call since it is a value that shouldn't change and
>> >would eliminate an unnecessary lock in the non-compound case.
>> 
>> This is reasonable, if no objection from others, I would change this in v2.
>
>Looks fine to me; I don't see it as a necessary improvement but there's 
>also no reason to object to it.  It's definitely a patch that is needed, 
>however, for the simple reason that with the existing code we can 
>manipulate the deferred split queue incorrectly so either way works for 
>me.  Feel free to keep my acked-by.

Ah, thanks David. You are so supportive.

-- 
Wei Yang
Help you, Help me