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SubjectRe: [PATCH 2/2] mm: Create non-atomic version of SetPageReserved for init use
On Wed 05-09-18 13:18:24, Alexander Duyck wrote:
> On Tue, Sep 4, 2018 at 11:24 PM Michal Hocko <mhocko@kernel.org> wrote:
> >
> > On Tue 04-09-18 11:33:45, Alexander Duyck wrote:
> > > From: Alexander Duyck <alexander.h.duyck@intel.com>
> > >
> > > It doesn't make much sense to use the atomic SetPageReserved at init time
> > > when we are using memset to clear the memory and manipulating the page
> > > flags via simple "&=" and "|=" operations in __init_single_page.
> > >
> > > This patch adds a non-atomic version __SetPageReserved that can be used
> > > during page init and shows about a 10% improvement in initialization times
> > > on the systems I have available for testing.
> >
> > I agree with Dave about a comment is due. I am also quite surprised that
> > this leads to such a large improvement. Could you be more specific about
> > your test and machines you were testing on?
>
> So my test case has been just initializing 4 3TB blocks of persistent
> memory with a few trace_printk values added to track total time in
> move_pfn_range_to_zone.
>
> What I have been seeing is that the time needed for the call drops on
> average from 35-36 seconds down to around 31-32.

This information belongs to the changelog.

>
> > Other than that the patch makes sense to me.
> >
> > > Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
> >
> > With the above addressed, feel free to add
> > Acked-by: Michal Hocko <mhocko@suse.com>
> >
> > Thanks!
>
> As far as adding a comment are we just talking about why it is
> reserved, or do we need a description of the __SetPageReserved versus
> SetPageReserved. For now I was looking at adding a comment like:

the later. The reason why we make it reserved should be quite clear. A
comment wouldn't hurt of course and what you have is a good start. But
it is usually atomic vs. non-atomic SetPage$Foo which needs some
clarification.

> @@ -5517,8 +5517,13 @@ void __meminit memmap_init_zone(unsigned long
> size, int nid, unsigned long zone,
> not_early:
> page = pfn_to_page(pfn);
> __init_single_page(page, pfn, zone, nid);
> +
> + /*
> + * Mark page reserved as it will need to wait for onlining
> + * phase for it to be fully associated with a zone.
> + */
> if (context == MEMMAP_HOTPLUG)
> - SetPageReserved(page);
> + __SetPageReserved(page);
>
> /*
> * Mark the block movable so that blocks are reserved for
>
> Any thoughts on this?
>
> Thanks.
>
> - Alex

--
Michal Hocko
SUSE Labs

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