linux-kernel - Re: [withdrawn] zsmalloc-remove-extra-cond_resched-in-__zs

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Message-ID: <20150326073916.GB26725@blaptop>
Date:	Thu, 26 Mar 2015 16:39:17 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:	akpm@...ux-foundation.org, sergey.senozhatsky@...il.com,
	ngupta@...are.org, sfr@...b.auug.org.au,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [withdrawn]
 zsmalloc-remove-extra-cond_resched-in-__zs_compact.patch removed from -mm
 tree

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@...ux-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 This patch was dropped because it was withdrawn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@...il.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@...il.com>
> > Cc: Minchan Kim <minchan@...nel.org>
> > Cc: Nitin Gupta <ngupta@...are.org>
> > Cc: Stephen Rothwell <sfr@...b.auug.org.au>
> > Signed-off-by: Andrew Morton <akpm@...ux-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@...nel.org>

> 
> 	-ss

-- 
Kind regards,
Minchan Kim
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