linux-kernel - Re: [withdrawn] zsmalloc-remove-extra-cond_resched-in-__zs

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Date:	Thu, 26 Mar 2015 17:13:13 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	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Subject: Re: [withdrawn]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

On (03/26/15 16:39), Minchan Kim wrote:
> Hello Sergey,
> 
> Sorry for slow response.
> I am overwhelmed with too much to do. :(
> 

Hello,
sure, no problem.

> > > 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))) {

> 
> 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).


in outer loop we have preemption enabled and unlocked class. wouldn't that help?
(hm, UP system?)

> 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>

thanks!

	-ss
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