linux-kernel - Re: [PATCH] mm: mlock: remove lru_add_drain

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Message-ID: <CALvZod6y6fBozZTJ=VEAXMoCaxB9Sjwp+L-JtTBAmyc53htxQw@mail.gmail.com>
Date:   Thu, 19 Oct 2017 13:14:52 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Minchan Kim <minchan@...nel.org>,
        Yisheng Xie <xieyisheng1@...wei.com>,
        Ingo Molnar <mingo@...nel.org>,
        Greg Thelen <gthelen@...gle.com>,
        Hugh Dickins <hughd@...gle.com>, Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: mlock: remove lru_add_drain_all()

On Thu, Oct 19, 2017 at 1:13 PM, Michal Hocko <mhocko@...nel.org> wrote:
> On Thu 19-10-17 12:46:50, Shakeel Butt wrote:
>> > [...]
>> >>
>> >> Sorry for the confusion. I wanted to say that if the pages which are
>> >> being mlocked are on caches of remote cpus then lru_add_drain_all will
>> >> move them to their corresponding LRUs and then remaining functionality
>> >> of mlock will move them again from their evictable LRUs to unevictable
>> >> LRU.
>> >
>> > yes, but the point is that we are draining pages which might be not
>> > directly related to pages which _will_ be mlocked by the syscall. In
>> > fact those will stay on the cache. This is the primary reason why this
>> > draining doesn't make much sense.
>> >
>> > Or am I still misunderstanding what you are saying here?
>> >
>>
>> lru_add_drain_all() will drain everything irrespective if those pages
>> are being mlocked or not.
>
> yes, let me be more specific. lru_add_drain_all will drain everything
> that has been cached at the time mlock is called. And that is not really
> related to the memory which will be faulted in (and cached) and mlocked
> by the syscall itself. Does it make more sense now?
>

Yes, you are absolutely right. Sorry for the confusion.