linux-kernel - Re: [PATCH 2/2] mm, memory_hotplug: remove timeout from __offline

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Message-ID: <20170904091505.xffd7orldpwlmrlx@dhcp22.suse.cz>
Date:   Mon, 4 Sep 2017 11:15:05 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Xishi Qiu <qiuxishi@...wei.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        Yasuaki Ishimatsu <yasu.isimatu@...il.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] mm, memory_hotplug: remove timeout from
 __offline_memory

On Mon 04-09-17 17:05:15, Xishi Qiu wrote:
> On 2017/9/4 17:01, Michal Hocko wrote:
> 
> > On Mon 04-09-17 16:58:30, Xishi Qiu wrote:
> >> On 2017/9/4 16:21, Michal Hocko wrote:
> >>
> >>> From: Michal Hocko <mhocko@...e.com>
> >>>
> >>> We have a hardcoded 120s timeout after which the memory offline fails
> >>> basically since the hot remove has been introduced. This is essentially
> >>> a policy implemented in the kernel. Moreover there is no way to adjust
> >>> the timeout and so we are sometimes facing memory offline failures if
> >>> the system is under a heavy memory pressure or very intensive CPU
> >>> workload on large machines.
> >>>
> >>> It is not very clear what purpose the timeout actually serves. The
> >>> offline operation is interruptible by a signal so if userspace wants
> >>
> >> Hi Michal,
> >>
> >> If the user know what he should do if migration for a long time,
> >> it is OK, but I don't think all the users know this operation
> >> (e.g. ctrl + c) and the affect.
> > 
> > How is this operation any different from other potentially long
> > interruptible syscalls?
> > 
> 
> Hi Michal,
> 
> I means the user should stop it by himself if migration always retry in endless.

If the memory is migrateable then the migration should finish
eventually. It can take some time but it shouldn't be an endless loop.
-- 
Michal Hocko
SUSE Labs