linux-kernel - Re: [PATCH v3 0/5] Introduce MADV_COLD and MADV

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Message-ID: <20190627231211.GA33052@google.com>
Date:   Fri, 28 Jun 2019 08:12:11 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-api@...r.kernel.org,
        Michal Hocko <mhocko@...e.com>,
        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>, oleksandr@...hat.com,
        hdanton@...a.com, lizeb@...gle.com,
        Dave Hansen <dave.hansen@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v3 0/5] Introduce MADV_COLD and MADV_PAGEOUT

On Thu, Jun 27, 2019 at 09:06:01PM +0300, Kirill A. Shutemov wrote:
> On Thu, Jun 27, 2019 at 08:54:00PM +0900, Minchan Kim wrote:
> > - Problem
> > 
> > Naturally, cached apps were dominant consumers of memory on the system.
> > However, they were not significant consumers of swap even though they are
> > good candidate for swap. Under investigation, swapping out only begins
> > once the low zone watermark is hit and kswapd wakes up, but the overall
> > allocation rate in the system might trip lmkd thresholds and cause a cached
> > process to be killed(we measured performance swapping out vs. zapping the
> > memory by killing a process. Unsurprisingly, zapping is 10x times faster
> > even though we use zram which is much faster than real storage) so kill
> > from lmkd will often satisfy the high zone watermark, resulting in very
> > few pages actually being moved to swap.
> 
> Maybe we should look if we do The Right Thing™ at system-wide level before
> introducing new API? How changing swappiness affects your workloads? What
> is swappiness value in your setup?

It was 100. Even, I tried 150 and 200 with simple hack of swappiness.
However, it caused too excessive swpout.

Anyway, systen-level tune is generally good but if process has hint, that
should work better and that's why advise API is.