Re: [withdrawn] zsmalloc-remove-extra-cond_resched-in-__zs_compact.patch removed from -mm tree

Re: [withdrawn] zsmalloc-remove-extra-cond_resched-in-__zs_compact.patch removed from -mm tree

[Sergey Senozhatsky]

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 This patch was dropped because it was withdrawn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?

	-ss

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Re: [withdrawn] zsmalloc-remove-extra-cond_resched-in-__zs_compact.patch removed from -mm tree

[Minchan Kim]

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 This patch was dropped because it was withdrawn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

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Re: [withdrawn] zsmalloc-remove-extra-cond_resched-in-__zs_compact.patch removed from -mm tree

[Sergey Senozhatsky]

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@kernel.org>

thanks!

	-ss

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Re: [withdrawn] zsmalloc-remove-extra-cond_resched-in-__zs_compact.patch removed from -mm tree

[Minchan Kim]

On Thu, Mar 26, 2015 at 05:13:13PM +0900, Sergey Senozhatsky wrote:
> 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 depends on preemption model. If you enable full preemption, you are right
but if you enable just voluntary preemption, cond_resched will help latency.

Thanks.

-- 
Kind regards,
Minchan Kim

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