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

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Message-ID: <20200109083438.GG4951@dhcp22.suse.cz>
Date:   Thu, 9 Jan 2020 09:34:38 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Wei Yang <richardw.yang@...ux.intel.com>
Cc:     hannes@...xchg.org, vdavydov.dev@...il.com,
        akpm@...ux-foundation.org, kirill.shutemov@...ux.intel.com,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, yang.shi@...ux.alibaba.com
Subject: Re: [RFC PATCH] mm: thp: grab the lock before manipulation defer list

On Thu 09-01-20 10:03:19, Wei Yang wrote:
> On Wed, Jan 08, 2020 at 10:40:41AM +0100, Michal Hocko wrote:
[...]
> >Moreover, look at the code you are trying to fix. Sure extending the
> >locking seem straightforward but does it result in a correct code
> >though? See my question in the previous email. How do we know that the
> >page is actually enqued in a non-empty list?
> 
> I may not get your point for the last sentence.
> 
> The list_empty() doesn't check the queue is empty but check the list, here is
> the page, is not enqueued into any list. Is this your concern?

My bad. For some reason I have misread the code and thought this was
get_deferred_split_queue rather than page_deferred_list. Sorry about the
confusion.
-- 
Michal Hocko
SUSE Labs