linux-kernel - Re: [PATCH 4/5] mm/hotplug: Avoid RCU stalls when removing large amounts of memory

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Date:   Mon, 17 Jun 2019 16:58:22 +1000
From:   "Alastair D'Silva" <alastair@...ilva.org>
To:     Mike Rapoport <rppt@...ux.ibm.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Oscar Salvador <osalvador@...e.com>,
        Michal Hocko <mhocko@...e.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Wei Yang <richard.weiyang@...il.com>,
        Juergen Gross <jgross@...e.com>, Qian Cai <cai@....pw>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jkosina@...e.cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Mukesh Ojha <mojha@...eaurora.org>,
        Arun KS <arunks@...eaurora.org>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Baoquan He <bhe@...hat.com>,
        Logan Gunthorpe <logang@...tatee.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] mm/hotplug: Avoid RCU stalls when removing large
 amounts of memory

On Mon, 2019-06-17 at 09:53 +0300, Mike Rapoport wrote:
> On Mon, Jun 17, 2019 at 02:36:30PM +1000, Alastair D'Silva wrote:
> > From: Alastair D'Silva <alastair@...ilva.org>
> > 
> > When removing sufficiently large amounts of memory, we trigger RCU
> > stall
> > detection. By periodically calling cond_resched(), we avoid bogus
> > stall
> > warnings.
> > 
> > Signed-off-by: Alastair D'Silva <alastair@...ilva.org>
> > ---
> >  mm/memory_hotplug.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> > index e096c987d261..382b3a0c9333 100644
> > --- a/mm/memory_hotplug.c
> > +++ b/mm/memory_hotplug.c
> > @@ -578,6 +578,9 @@ void __remove_pages(struct zone *zone, unsigned
> > long phys_start_pfn,
> >  		__remove_section(zone, __pfn_to_section(pfn),
> > map_offset,
> >  				 altmap);
> >  		map_offset = 0;
> > +
> > +		if (!(i & 0x0FFF))
> 
> No magic numbers please. And a comment would be appreciated.
> 

Agreed, thanks for the review.

-- 
Alastair D'Silva           mob: 0423 762 819
skype: alastair_dsilva    
Twitter: @EvilDeece
blog: http://alastair.d-silva.org