linux-kernel - Re: [PATCH 3/7] mm: rework __isolate_lru

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Message-ID: <4F51E243.5050804@openvz.org>
Date:	Sat, 03 Mar 2012 13:20:03 +0400
From:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
To:	Hugh Dickins <hughd@...gle.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <jweiner@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/7] mm: rework __isolate_lru_page() file/anon filter

Konstantin Khlebnikov wrote:
> Hugh Dickins wrote:
>> On Wed, 29 Feb 2012, Konstantin Khlebnikov wrote:
>>
>>> This patch adds file/anon filter bits into isolate_mode_t,
>>> this allows to simplify checks in __isolate_lru_page().
>>>
>>> Signed-off-by: Konstantin Khlebnikov<khlebnikov@...nvz.org>
>>
>> Almost-Acked-by: Hugh Dickins<hughd@...gle.com>
>>
>> with one whitespace nit, and one functional addition requested.
>>
>> I'm perfectly happy with your :?s myself, but some people do dislike
>> them.  I'm happy with the switch alternative if it's as efficient:
>> something that surprised me very much when trying to get convincing
>> performance numbers for per-memcg per-zone lru_lock at home...
>>
>> ... __isolate_lru_page() featured astonishly high on the perf report
>> of streaming from files on ext4 on /dev/ram0 to /dev/null, coming
>> immediately below the obvious zeroing and copying: okay, the zeroing
>> and copying were around 30% each, and __isolate_lru_page() down around
>> 2% or below, but even so it seemed very odd that it should feature so
>> high, and any optimizations to it very welcome - unless it was purely
>> some bogus result.
>
> Actually ANON/FILE ACTIVE/INACTIVE checks does not required at non-lumpy reclaim
> (all pages are picked from right lru list) and compaction (it does not care).
> But seems like removing these two bit-checks cannot give noticeable performance gain.
>
> This patch can be postponed. It does not so important and
> it does not share context with other patches in this set.

Oops, no it cannot be dropped. Next patch "mm: push lru index into shrink_[in]active_list()"
kills "file" variable in isolate_lru_pages(). I sent v2 for this patch only.

>
>>
>>> ---
>>>    include/linux/mmzone.h |    4 ++++
>>>    include/linux/swap.h   |    2 +-
>>>    mm/compaction.c        |    5 +++--
>>>    mm/vmscan.c            |   27 +++++++++++++--------------
>>>    4 files changed, 21 insertions(+), 17 deletions(-)
>>>
>>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
>>> index eff4918..2fed935 100644
>>> --- a/include/linux/mmzone.h
>>> +++ b/include/linux/mmzone.h
>>> @@ -193,6 +193,10 @@ struct lruvec {
>>>    #define ISOLATE_UNMAPPED	((__force isolate_mode_t)0x8)
>>>    /* Isolate for asynchronous migration */
>>>    #define ISOLATE_ASYNC_MIGRATE	((__force isolate_mode_t)0x10)
>>> +/* Isolate swap-backed pages */
>>> +#define	ISOLATE_ANON		((__force isolate_mode_t)0x20)
>>> +/* Isolate file-backed pages */
>>> +#define	ISOLATE_FILE		((__force isolate_mode_t)0x40)
>>
>>    From the patch you can see that the #defines above yours used a
>> space where you have used a tab: better to use a space as above.
>>
>>> @@ -375,7 +376,7 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
>>>    			mode |= ISOLATE_ASYNC_MIGRATE;
>>>
>>>    		/* Try isolate the page */
>>> -		if (__isolate_lru_page(page, mode, 0) != 0)
>>> +		if (__isolate_lru_page(page, mode) != 0)
>>>    			continue;
>>
>> I thought you were missing something there, but no, that's rather
>> the case you are simplifying.  However...
>>
>>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>>> index af6cfe7..1b70338 100644
>>> --- a/mm/vmscan.c
>>> +++ b/mm/vmscan.c
>>> @@ -1520,6 +1511,10 @@ shrink_inactive_list(unsigned long nr_to_scan, struct mem_cgroup_zone *mz,
>>>    		isolate_mode |= ISOLATE_UNMAPPED;
>>>    	if (!sc->may_writepage)
>>>    		isolate_mode |= ISOLATE_CLEAN;
>>> +	if (file)
>>> +		isolate_mode |= ISOLATE_FILE;
>>> +	else
>>> +		isolate_mode |= ISOLATE_ANON;
>>
>> Above here, under "if (sc->reclaim_mode&   RECLAIM_MODE_LUMPYRECLAIM)",
>> don't you need
>>
>> 		isolate_mode |= ISOLATE_ACTIVE | ISOLATE_FILE | ISOLATE_ANON;
>>
>> now to reproduce the same "all_lru_mode" behaviour as before?
>
> Yes, I missed this. Thanks.
>
>>
>> Hugh
>
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