linux-kernel - Re: [RFC 0/7] introduce memory hinting API for external process

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Message-ID: <20190521063421.GG32329@dhcp22.suse.cz>
Date:   Tue, 21 May 2019 08:34:21 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Minchan Kim <minchan@...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>, linux-api@...r.kernel.org
Subject: Re: [RFC 0/7] introduce memory hinting API for external process

[linux-api]

On Mon 20-05-19 18:44:52, Matthew Wilcox wrote:
> On Mon, May 20, 2019 at 12:52:47PM +0900, Minchan Kim wrote:
> > IMHO we should spell it out that this patchset complements MADV_WONTNEED
> > and MADV_FREE by adding non-destructive ways to gain some free memory
> > space. MADV_COLD is similar to MADV_WONTNEED in a way that it hints the
> > kernel that memory region is not currently needed and should be reclaimed
> > immediately; MADV_COOL is similar to MADV_FREE in a way that it hints the
> > kernel that memory region is not currently needed and should be reclaimed
> > when memory pressure rises.
> 
> Do we tear down page tables for these ranges?  That seems like a good
> way of reclaiming potentially a substantial amount of memory.

I do not think we can in general because this is a non-destructive
operation. So at least we cannot tear down anonymous ptes (they will
turn into swap entries).

-- 
Michal Hocko
SUSE Labs