linux-kernel - Re: [PATCH 2/2] mm: do not warn on offline nodes unless the specific node is explicitly requested

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Message-ID: <20180523140601.GQ20441@dhcp22.suse.cz>
Date:   Wed, 23 May 2018 16:06:02 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...hadventures.net>,
        Vlastimil Babka <vbabka@...e.cz>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [PATCH 2/2] mm: do not warn on offline nodes unless the specific
 node is explicitly requested

On Wed 23-05-18 19:15:51, Anshuman Khandual wrote:
> On 05/23/2018 06:25 PM, Michal Hocko wrote:
> > when adding memory to a node that is currently offline.
> > 
> > The VM_WARN_ON is just too loud without a good reason. In this
> > particular case we are doing
> > 	alloc_pages_node(node, GFP_KERNEL|__GFP_RETRY_MAYFAIL|__GFP_NOWARN, order)
> > 
> > so we do not insist on allocating from the given node (it is more a
> > hint) so we can fall back to any other populated node and moreover we
> > explicitly ask to not warn for the allocation failure.
> > 
> > Soften the warning only to cases when somebody asks for the given node
> > explicitly by __GFP_THISNODE.
> 
> node hint passed here eventually goes into __alloc_pages_nodemask()
> function which then picks up the applicable zonelist irrespective of
> the GFP flag __GFP_THISNODE.

__GFP_THISNODE should enforce the given node without any fallbacks
unless something has changed recently.

> Though we can go into zones of other
> nodes if the present node (whose zonelist got picked up) does not
> have any memory in it's zones. So warning here might not be without
> any reason.

I am not sure I follow. Are you suggesting a different VM_WARN_ON?
-- 
Michal Hocko
SUSE Labs