linux-kernel - Re: [RFC 4/7] mm: factor out madvise's core functionality

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Message-ID: <20190521105256.GF219653@google.com>
Date:   Tue, 21 May 2019 19:52:56 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Oleksandr Natalenko <oleksandr@...hat.com>
Cc:     Michal Hocko <mhocko@...nel.org>,
        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>,
        Daniel Colascione <dancol@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Sonny Rao <sonnyrao@...gle.com>,
        Brian Geffon <bgeffon@...gle.com>
Subject: Re: [RFC 4/7] mm: factor out madvise's core functionality

On Tue, May 21, 2019 at 09:06:38AM +0200, Oleksandr Natalenko wrote:
> Hi.
> 
> On Tue, May 21, 2019 at 08:50:00AM +0200, Michal Hocko wrote:
> > On Tue 21-05-19 08:36:28, Oleksandr Natalenko wrote:
> > [...]
> > > Regarding restricting the hints, I'm definitely interested in having
> > > remote MADV_MERGEABLE/MADV_UNMERGEABLE. But, OTOH, doing it via remote
> > > madvise() introduces another issue with traversing remote VMAs reliably.
> > > IIUC, one can do this via userspace by parsing [s]maps file only, which
> > > is not very consistent, and once some range is parsed, and then it is
> > > immediately gone, a wrong hint will be sent.
> > > 
> > > Isn't this a problem we should worry about?
> > 
> > See http://lkml.kernel.org/r/20190520091829.GY6836@dhcp22.suse.cz
> 
> Oh, thanks for the pointer.
> 
> Indeed, for my specific task with remote KSM I'd go with map_files
> instead. This doesn't solve the task completely in case of traversal
> through all the VMAs in one pass, but makes it easier comparing to a
> remote syscall.

I'm wondering how map_files can solve your concern exactly if you have
a concern about the race of vma unmap/remap even there are anonymous
vma which map_files doesn't support.

> 
> -- 
>   Best regards,
>     Oleksandr Natalenko (post-factum)
>     Senior Software Maintenance Engineer