linux-kernel - Re: [RFC 1/7] mm: introduce MADV

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Message-ID: <20190520081943.GW6836@dhcp22.suse.cz>
Date:   Mon, 20 May 2019 10:19:43 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     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 1/7] mm: introduce MADV_COOL

On Mon 20-05-19 10:16:21, Michal Hocko wrote:
> [CC linux-api]
> 
> On Mon 20-05-19 12:52:48, Minchan Kim wrote:
> > When a process expects no accesses to a certain memory range
> > it could hint kernel that the pages can be reclaimed
> > when memory pressure happens but data should be preserved
> > for future use.  This could reduce workingset eviction so it
> > ends up increasing performance.
> > 
> > This patch introduces the new MADV_COOL hint to madvise(2)
> > syscall. MADV_COOL can be used by a process to mark a memory range
> > as not expected to be used in the near future. The hint can help
> > kernel in deciding which pages to evict early during memory
> > pressure.
> 
> I do not want to start naming fight but MADV_COOL sounds a bit
> misleading. Everybody thinks his pages are cool ;). Probably MADV_COLD
> or MADV_DONTNEED_PRESERVE.

OK, I can see that you have used MADV_COLD for a different mode.
So this one is effectively a non destructive MADV_FREE alternative
so MADV_FREE_PRESERVE would sound like a good fit. Your MADV_COLD
in other patch would then be MADV_DONTNEED_PRESERVE. Right?

-- 
Michal Hocko
SUSE Labs