linux-kernel - Re: [PATCH 2/3] check unevictable flag in lumy reclaim v2

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Message-ID: <28c262360906110237u1f3d1877hae54a51575955549@mail.gmail.com>
Date:	Thu, 11 Jun 2009 18:37:40 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	apw@...onical.com, riel@...hat.com, mel@....ul.ie
Subject: Re: [PATCH 2/3] check unevictable flag in lumy reclaim v2

On Thu, Jun 11, 2009 at 5:38 PM, KAMEZAWA
Hiroyuki<kamezawa.hiroyu@...fujitsu.com> wrote:
> How about this ?
>
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>
> Lumpy reclaim check pages from their pfn. Then, it can find unevictable pages
> in its loop.
> Abort lumpy reclaim when we find Unevictable page, we never get a lump
> of pages for requested order.
>
> Changelog: v1->v2
>  - rewrote commet.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> ---
>  mm/vmscan.c |    9 +++++++++
>  1 file changed, 9 insertions(+)
>
> Index: lumpy-reclaim-trial/mm/vmscan.c
> ===================================================================
> --- lumpy-reclaim-trial.orig/mm/vmscan.c
> +++ lumpy-reclaim-trial/mm/vmscan.c
> @@ -936,6 +936,15 @@ static unsigned long isolate_lru_pages(u
>                        /* Check that we have not crossed a zone boundary. */
>                        if (unlikely(page_zone_id(cursor_page) != zone_id))
>                                continue;
> +                       /*
> +                        * We tries to free all pages in this range to create
> +                        * a free large page. Then, if the range includes a page
> +                        * never be reclaimed, we have no reason to do more.
> +                        * PageUnevictable page is not a page which can be
> +                        * easily freed. Abort this scan now.
> +                        */
> +                       if (unlikely(PageUnevictable(cursor_page)))
> +                               break;

__isolate_lru_pages already checked PageUnevictable to return error.
I want to remove repeated check although it is trivial.

By your patch, It seems to remove PageUnevictable check in __isolate_lru_pages.

But I know that. If we remove PageUnevictable check in
__isolate_lru_pages, it can't go into BUG in non-lumpy case. ( I
mentioned following as code)

                case -EBUSY:
                        /* else it is being freed elsewhere */
                        list_move(&page->lru, src);
                        continue;

                default:
                        BUG();
                }


It means we can remove BUG in non-lumpy case and then add BUG into
__isolate_lru_pages directly.

If we can do it, we can remove unnecessary PageUnevictable check in
__isolate_lru_page.

I am not sure this is right in case of memcg.

-- 
Kinds regards,
Minchan Kim
--
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