linux-kernel - Re: [PATCH 3/7 v2] mm: rework __isolate_lru

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Message-ID: <4F5AFAF0.6060608@openvz.org>
Date:	Sat, 10 Mar 2012 10:55:44 +0400
From:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
To:	Hugh Dickins <hughd@...gle.com>
CC:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <jweiner@...hat.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/7 v2] mm: rework __isolate_lru_page() file/anon filter

Hugh Dickins wrote:
> On Fri, 9 Mar 2012, Konstantin Khlebnikov wrote:
>> Hugh Dickins wrote:
>>>
>>> I like very much the look of what he's come up with, but I'm still
>>> puzzling over why it barely makes any improvement to __isolate_lru_page():
>>> seems significantly inferior (in code size terms) to his original (which
>>> I imagine Glauber's compromise would be equivalent to).
>>>
>>> At some point I ought to give up on niggling about this,
>>> but I haven't quite got there yet.
>>
>> (with if())
>> $ ./scripts/bloat-o-meter built-in.o built-in.o-v1
>> add/remove: 0/0 grow/shrink: 2/1 up/down: 32/-20 (12)
>> function                                     old     new   delta
>> static.shrink_active_list                    837     853     +16
>> shrink_inactive_list                        1259    1275     +16
>> static.isolate_lru_pages                    1055    1035     -20
>>
>> (with switch())
>> $ ./scripts/bloat-o-meter built-in.o built-in.o-v2
>> add/remove: 0/0 grow/shrink: 4/2 up/down: 111/-23 (88)
>> function                                     old     new   delta
>> __isolate_lru_page                           301     377     +76
>> static.shrink_active_list                    837     853     +16
>> shrink_inactive_list                        1259    1275     +16
>> page_evictable                               170     173      +3
>> __remove_mapping                             322     319      -3
>> static.isolate_lru_pages                    1055    1035     -20
>>
>> (without __always_inline on page_lru())
>> $ ./scripts/bloat-o-meter built-in.o built-in.o-v5-noinline
>> add/remove: 0/0 grow/shrink: 5/2 up/down: 93/-23 (70)
>> function                                     old     new   delta
>> __isolate_lru_page                           301     333     +32
>> isolate_lru_page                             359     385     +26
>> static.shrink_active_list                    837     853     +16
>> putback_inactive_pages                       635     651     +16
>> page_evictable                               170     173      +3
>> __remove_mapping                             322     319      -3
>> static.isolate_lru_pages                    1055    1035     -20
>>
>> $ ./scripts/bloat-o-meter built-in.o built-in.o-v5
>> add/remove: 0/0 grow/shrink: 3/4 up/down: 35/-67 (-32)
>> function                                     old     new   delta
>> static.shrink_active_list                    837     853     +16
>> __isolate_lru_page                           301     317     +16
>> page_evictable                               170     173      +3
>> __remove_mapping                             322     319      -3
>> mem_cgroup_lru_del                            73      65      -8
>> static.isolate_lru_pages                    1055    1035     -20
>> __mem_cgroup_commit_charge                   676     640     -36
>>
>> Actually __isolate_lru_page() even little bit bigger
>
> I was coming to realize that it must be your page_lru()ing:
> although it's dressed up in one line, there's several branches there.

Yes, but I think we can optimize page_lru(): we can prepare ready-to-use
page lru index in lower bits of page->flags, if we swap page flags and split
LRU_UNEVICTABLE into FILE/ANON parts.

>
> I think you'll find you have a clear winner at last, if you just pass
> lru on down as third arg to __isolate_lru_page(), where file used to
> be passed, instead of re-evaluating it inside.
>
> shrink callers already have the lru, and compaction works it out
> immediately afterwards.

No, for non-lumpy isolation we don't need this check at all,
because all pages already picked from right lru list.

I'll send separate patch for this (on top v5 patchset), after meditation =)

>
> Though we do need to be careful: the lumpy case would then have to
> pass page_lru(cursor_page).  Oh, actually no (though it would deserve
> a comment): since the lumpy case selects LRU_ALL_EVICTABLE, it's
> irrelevant what it passes for lru, so might as well stick with
> the one passed down.  Though you may decide I'm being too tricky
> there, and prefer to calculate page_lru(cursor_page) anyway, it
> not being the hottest path.
>
> Whether you'd still want page_lru(page) __always_inline, I don't know.
>
> Hugh

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