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Message-ID: <4FF4EF8E.4080706@cn.fujitsu.com>
Date: Thu, 05 Jul 2012 09:36:14 +0800
From: Lai Jiangshan <laijs@...fujitsu.com>
To: Mel Gorman <mel@....ul.ie>
CC: Chris Metcalf <cmetcalf@...era.com>, Len Brown <lenb@...nel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Andi Kleen <andi@...stfloor.org>, Julia Lawall <julia@...u.dk>,
David Howells <dhowells@...hat.com>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Kay Sievers <kay.sievers@...y.org>,
Ingo Molnar <mingo@...e.hu>,
Paul Gortmaker <paul.gortmaker@...driver.com>,
Daniel Kiper <dkiper@...-space.pl>,
Andrew Morton <akpm@...ux-foundation.org>,
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
Michal Hocko <mhocko@...e.cz>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
Minchan Kim <minchan@...nel.org>,
Michal Nazarewicz <mina86@...a86.com>,
Marek Szyprowski <m.szyprowski@...sung.com>,
Rik van Riel <riel@...hat.com>,
Bjorn Helgaas <bhelgaas@...gle.com>,
Christoph Lameter <cl@...ux.com>,
David Rientjes <rientjes@...gle.com>,
linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
linux-mm@...ck.org
Subject: Re: [RFC PATCH 1/3 V1] mm, page_alloc: use __rmqueue_smallest when
borrow memory from MIGRATE_CMA
On 07/04/2012 07:19 PM, Mel Gorman wrote:
> On Wed, Jul 04, 2012 at 06:43:47PM +0800, Lai Jiangshan wrote:
>> On 07/04/2012 06:17 PM, Mel Gorman wrote:
>>> On Wed, Jul 04, 2012 at 03:26:16PM +0800, Lai Jiangshan wrote:
>>>> The pages of MIGRATE_CMA can't not be changed to the other type,
>>>> nor be moved to the other free list.
>>>>
>>>> ==>
>>>> So when we use __rmqueue_fallback() to borrow memory from MIGRATE_CMA,
>>>> one of the highest order page is borrowed and it is split.
>>>> But the free pages resulted by splitting can NOT
>>>> be moved to MIGRATE_MOVABLE.
>>>>
>>>> ==>
>>>> So in the next time of allocation, we NEED to borrow again,
>>>> another one of the highest order page is borrowed from CMA and it is split.
>>>> and results some other new split free pages.
>>>>
>>>
>>> Then special case __rmqueue_fallback() to move pages stolen from
>>> MIGRATE_CMA to the MIGRATE_MOVABLE lists but do not change the pageblock
>>> type.
>>
>> Because unmovable-page-requirement can allocate page from
>> MIGRATE_MOVABLE free list. So We can not move MIGRATE_CMA pages
>> to the MIGRATE_MOVABLE free list.
>>
>
> Ok, good point.
>
>> See here:
>>
>> MOVABLE list is empty
>> UNMOVABLE list is empty
>> movable-page-requirement
>> borrow from CMA list
>> split it, others are put into UNMOVABLE list
>> unmovable-page-requiremnt
>> borrow from UNMOVABLE list
>> NOW, it is BUG, we use CMA pages for unmovable usage.
>>
>
> The patch still looks unnecessarily complex for what you are trying to
Which is complex in my code? __rmqueue_smallest()? __rmqueue_fallback()?
__rmqueue_smallest() ? I think it is required.
__rmqueue_fallback()?
It is just a cleanup for __rmqueue_fallback(), CMA is removed out from
__rmqueue_fallback(), so we can cleanup fallback(). I will remove/split
the cleanup part of the patch in next round.
> achieve and as a result I'm not reviewing it as carefully as I should.
> It looks like the entire patch boiled down to this hunk here
>
> +#ifdef CONFIG_CMA
> + if (unlikely(!page) && migratetype == MIGRATE_MOVABLE)
> + page = __rmqueue_smallest(zone, order, MIGRATE_CMA);
> +#endif
> +
>
> With that in place, this would would need to change from
>
> [MIGRATE_MOVABLE] = { MIGRATE_CMA, MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE, MIGRATE_RESERVE },
>
> to
>
> [MIGRATE_MOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE, MIGRATE_RESERVE },
>
> because the fallback is already being handled as a special case. Leave
> the other fallback logic as it is.
>
> This is not tested at all and is only meant to illustrate why I think
> your patch looks excessively complex for what you are trying to
> achieve.
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 4beb7ae..0063e93 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -895,11 +895,9 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
> static int fallbacks[MIGRATE_TYPES][4] = {
> [MIGRATE_UNMOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE, MIGRATE_RESERVE },
> [MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE, MIGRATE_MOVABLE, MIGRATE_RESERVE },
> + [MIGRATE_MOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE, MIGRATE_RESERVE },
> #ifdef CONFIG_CMA
> - [MIGRATE_MOVABLE] = { MIGRATE_CMA, MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE, MIGRATE_RESERVE },
> [MIGRATE_CMA] = { MIGRATE_RESERVE }, /* Never used */
> -#else
> - [MIGRATE_MOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE, MIGRATE_RESERVE },
> #endif
> [MIGRATE_RESERVE] = { MIGRATE_RESERVE }, /* Never used */
> [MIGRATE_ISOLATE] = { MIGRATE_RESERVE }, /* Never used */
> @@ -1076,6 +1074,20 @@ static struct page *__rmqueue(struct zone *zone, unsigned int order,
>
> retry_reserve:
> page = __rmqueue_smallest(zone, order, migratetype);
> +#ifdef CONFIG_CMA
> + if (!unlikely(!page) && migratetype == MIGRATE_MOVABLE) {
> +
> + /*
> + * CMA is a special case where we want to use
> + * the smallest available page instead of splitting
> + * the largest chunks. We still must avoid the pages
> + * moving to MIGRATE_MOVABLE where they might be
> + * used for UNRECLAIMABLE or UNMOVABLE allocations
> + */
> + migratetype = MIGRATE_CMA;
> + goto retry_reserve;
> + }
> +#endif /* CONFIG_CMA */
>
> if (unlikely(!page) && migratetype != MIGRATE_RESERVE) {
need to add
+ if (migratetype == MIGRATE_CMA)
+ migratetype = MIGRATE_MOVABLE;
to restore the migratetype for fallback.
And your code are the same as mine in the view of CPU:
__rmqueue_smallest(MIGRATE_MOVABLE)
if failed: __rmqueue_smallest(MIGRATE_CMA)
if failed: __rmqueue_fallback()
if failed: __rmqueue_smallest(MIGRATE_RESERVE)
The differences are:
you just use "goto" instead "if" for instruction control.
your code are longer.
the number of branch in your code = mine + 1
My code have better readability:
Mine:
========================================================================
page = __rmqueue_smallest(zone, order, migratetype);
#ifdef CONFIG_CMA
if (unlikely(!page) && migratetype == MIGRATE_MOVABLE)
page = __rmqueue_smallest(zone, order, MIGRATE_CMA);
#endif
if (unlikely(!page))
page = __rmqueue_fallback(zone, order, migratetype);
if (unlikely(!page))
page = __rmqueue_smallest(zone, order, MIGRATE_RESERVE);
trace_mm_page_alloc_zone_locked(page, order, migratetype);
return page;
=====================================================================
Yours:
==================================================================
retry_reserve:
page = __rmqueue_smallest(zone, order, migratetype);
#ifdef CONFIG_CMA
if (!unlikely(!page) && migratetype == MIGRATE_MOVABLE) {
/*
* CMA is a special case where we want to use
* the smallest available page instead of splitting
* the largest chunks. We still must avoid the pages
* moving to MIGRATE_MOVABLE where they might be
* used for UNRECLAIMABLE or UNMOVABLE allocations
*/
migratetype = MIGRATE_CMA;
goto retry_reserve;
}
#endif /* CONFIG_CMA */
if (unlikely(!page) && migratetype != MIGRATE_RESERVE) {
if (migratetype == MIGRATE_CMA)
migratetype = MIGRATE_MOVABLE;
page = __rmqueue_fallback(zone, order, migratetype);
/*
* Use MIGRATE_RESERVE rather than fail an allocation. goto
* is used because __rmqueue_smallest is an inline function
* and we want just one call site
*/
if (!page) {
migratetype = MIGRATE_RESERVE;
goto retry_reserve;
}
}
trace_mm_page_alloc_zone_locked(page, order, migratetype);
return page;
==========================================================================
How about this one? (just type it in the email client)
#define RMQUEUE_FALLBACK 1024
int rmqueue_list[3][4] = {
[MIGRATE_UNMOVABLE] = { MIGRATE_UNMOVABLE, RMQUEUE_FALLBACK, MIGRATE_RESERVE},
[MIGRATE_RECLAIMABLE] = { MIGRATE_RECLAIMABLE, RMQUEUE_FALLBACK, MIGRATE_RESERVE},
[MIGRATE_MOVABLE] = {MIGRATE_MOVABLE, MIGRATE_CMA, RMQUEUE_FALLBACK, MIGRATE_RESERVE},
}
static struct page *__rmqueue(struct zone *zone, unsigned int order,
int migratetype)
{
struct page *page;
int i, mt;
for (i = 0; ; i++) {
mt = rmqueue_list[migratetype][i];
if (likely(mt != RMQUEUE_FALLBACK)
page = __rmqueue_smallest(zone, order, mt);
else
page = __rmqueue_fallback(zone, order, migratetype);
/* MIGRATE_RESERVE is always the last one */
if (likely(page) || (mt == MIGRATE_RESERVE))
break;
}
trace_mm_page_alloc_zone_locked(page, order, migratetype);
return page;
}
Thanks,
Lai
> page = __rmqueue_fallback(zone, order, migratetype);
> --
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