Re: [withdrawn] zsmalloc-remove-extra-cond_resched-in-__zs_compact.patch removed from -mm tree

Minchan Kim
2015-03-26T07:39:25Z

Hello Sergey,

Sorry for slow response.
I am overwhelmed with too much to do. :(

On Thu, Mar 26, 2015 at 09:27:17AM +0900, Sergey Senozhatsky wrote:
> On (03/25/15 13:25), akpm@linux-foundation.org wrote:
> > The patch titled
> > Subject: zsmalloc: remove extra cond_resched() in __zs_compact
> > has been removed from the -mm tree. Its filename was
> > zsmalloc-remove-extra-cond_resched-in-__zs_compact.patch
> >
> > This patch was dropped because it was withdrawn
> >
> > ------------------------------------------------------
> > From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> > Subject: zsmalloc: remove extra cond_resched() in __zs_compact
> >
> > Do not perform cond_resched() before the busy compaction loop in
> > __zs_compact(), because this loop does it when needed.
> >
> > Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> > Cc: Minchan Kim <minchan@kernel.org>
> > Cc: Nitin Gupta <ngupta@vflare.org>
> > Cc: Stephen Rothwell <sfr@canb.auug.org.au>
> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> > ---
> >
> > mm/zsmalloc.c | 2 --
> > 1 file changed, 2 deletions(-)
> >
> > diff -puN mm/zsmalloc.c~zsmalloc-remove-extra-cond_resched-in-__zs_compact mm/zsmalloc.c
> > --- a/mm/zsmalloc.c~zsmalloc-remove-extra-cond_resched-in-__zs_compact
> > +++ a/mm/zsmalloc.c
> > @@ -1717,8 +1717,6 @@ static unsigned long __zs_compact(struct
> > struct page *dst_page = NULL;
> > unsigned long nr_total_migrated = 0;
> >
> > - cond_resched();
> > -
> > spin_lock(&class->lock);
> > while ((src_page = isolate_source_page(class))) {
> >
>
> Hello,
>
> Minchan, did I miss your NACK on this patch? or could you please ACK it?

I saw this patch yesterday night but didn't acked intentionally because
I was not sure and too tired to see the code so I postpone.

If we removed cond_resched out of outer loop(ie, your patch), we lose
the chance to reschedule if alloc_target_page fails(ie, there is no
zspage in ZS_ALMOST_FULL and ZS_ALMOST_EMPTY).
It might be not rare event if we does compation successfully for a
size_class. However, with next coming higher size_class for __zs_compact,
we will encounter cond_resched during compaction.
So, I am happy to ack. :)

Acked-by: Minchan Kim <minchan@kernel.org>

>
> -ss

--
Kind regards,
Minchan Kim