linux-kernel - Re: [PATCH v2 2/5] mm: introduce external memory hinting API

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Message-ID: <20200123072904.ludphxkxseyg2qli@butterfly.localdomain>
Date:   Thu, 23 Jan 2020 08:29:04 +0100
From:   Oleksandr Natalenko <oleksandr@...hat.com>
To:     Minchan Kim <minchan@...nel.org>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, linux-api@...r.kernel.org,
        Suren Baghdasaryan <surenb@...gle.com>,
        Tim Murray <timmurray@...gle.com>,
        Daniel Colascione <dancol@...gle.com>,
        Sandeep Patil <sspatil@...gle.com>,
        Sonny Rao <sonnyrao@...gle.com>,
        Brian Geffon <bgeffon@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        John Dias <joaodias@...gle.com>, ktkhai@...tuozzo.com,
        christian.brauner@...ntu.com, sjpark@...zon.de
Subject: Re: [PATCH v2 2/5] mm: introduce external memory hinting API

On Wed, Jan 22, 2020 at 05:43:16PM -0800, Minchan Kim wrote:
> > It seems I've overlooked an important piece of this submission: one
> > cannot apply the hint to all the anonymous mapping regardless of address
> > range. For KSM I'd rather either have a possibility to hint all the
> > anonymous mappings, or, as it was suggested previously, be able to iterate
> > over existing mappings using some (fd-based?) API.
> 
> Thing is how you could identify a certan range is better for KSM than
> others from external process?

I think the info like this is kinda available via /proc/pid/smaps. It
lists the ranges and the vmflags. But using it raises 2 concerns: one is
the absence of guarantee the mappings won't change after smaps is read
and the second one is that there's no separate vmflag for marking a vma
as non-meregable (and IIRC from previous attempts on addressing this,
we've already exhausted all the flags on 32-bit arches, so it is not
something that can be trivially addressed).

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