linux-kernel - Re: [RFC 6/7] mm: extend process_madvise syscall to support vector arrary

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Message-ID: <20190530184713.GI6703@dhcp22.suse.cz>
Date:   Thu, 30 May 2019 20:47:13 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Daniel Colascione <dancol@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Tim Murray <timmurray@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Sonny Rao <sonnyrao@...gle.com>,
        Brian Geffon <bgeffon@...gle.com>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [RFC 6/7] mm: extend process_madvise syscall to support vector
 arrary

On Thu 30-05-19 17:02:14, Minchan Kim wrote:
> On Thu, May 30, 2019 at 08:57:55AM +0200, Michal Hocko wrote:
> > On Thu 30-05-19 11:17:48, Minchan Kim wrote:
[...]
> > > First time, I didn't think about atomicity about address range race
> > > because MADV_COLD/PAGEOUT is not critical for the race.
> > > However you raised the atomicity issue because people would extend
> > > hints to destructive ones easily. I agree with that and that's why
> > > we discussed how to guarantee the race and Daniel comes up with good idea.
> > 
> > Just for the clarification, I didn't really mean atomicity but rather a
> > _consistency_ (essentially time to check to time to use consistency).
> 
> What do you mean by *consistency*? Could you elaborate it more?

That you operate on the object you have got by some means. In other
words that the range you want to call madvise on hasn't been
remapped/replaced by a different mmap operation.

-- 
Michal Hocko
SUSE Labs