linux-kernel - Re: [PATCH] mm: fix draining remote pageset

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Message-ID: <ZNxxaFnM9W8+imHD@dhcp22.suse.cz>
Date:   Wed, 16 Aug 2023 08:49:12 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Christoph Lameter <cl@...ux.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH] mm: fix draining remote pageset

On Mon 14-08-23 09:59:51, Huang, Ying wrote:
> Hi, Michal,
> 
> Michal Hocko <mhocko@...e.com> writes:
> 
> > On Fri 11-08-23 17:08:19, Huang Ying wrote:
> >> If there is no memory allocation/freeing in the remote pageset after
> >> some time (3 seconds for now), the remote pageset will be drained to
> >> avoid memory wastage.
> >> 
> >> But in the current implementation, vmstat updater worker may not be
> >> re-queued when we are waiting for the timeout (pcp->expire != 0) if
> >> there are no vmstat changes, for example, when CPU goes idle.
> >
> > Why is that a problem?
> 
> The pages of the remote zone may be kept in the local per-CPU pageset
> for long time as long as there's no page allocation/freeing on the
> logical CPU.  In addition to the logical CPU goes idle, this is also
> possible if the logical CPU is busy in the user space.

But why is this a problem? Is the scale of the problem sufficient to
trigger out of memory situations or be otherwise harmful?

-- 
Michal Hocko
SUSE Labs