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

[Minchan Kim]

On Thu, Jun 11, 2009 at 5:38 PM, KAMEZAWA
Hiroyuki<kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> How about this ?
>
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
>
> 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
> Â- rewrote commet.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> ---
> Âmm/vmscan.c | Â Â9 +++++++++
> Â1 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
> Â Â Â Â Â Â Â Â Â Â Â Â/* Check that we have not crossed a zone boundary. */
> Â Â Â Â Â Â Â Â Â Â Â Âif (unlikely(page_zone_id(cursor_page) != zone_id))
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Âcontinue;
> + Â Â Â Â Â Â Â Â Â Â Â /*
> + Â Â Â Â Â Â Â Â Â Â Â Â* We tries to free all pages in this range to create
> + Â Â Â Â Â Â Â Â Â Â Â Â* a free large page. Then, if the range includes a page
> + Â Â Â Â Â Â Â Â Â Â Â Â* never be reclaimed, we have no reason to do more.
> + Â Â Â Â Â Â Â Â Â Â Â Â* PageUnevictable page is not a page which can be
> + Â Â Â Â Â Â Â Â Â Â Â Â* easily freed. Abort this scan now.
> + Â Â Â Â Â Â Â Â Â Â Â Â*/
> + Â Â Â Â Â Â Â Â Â Â Â if (unlikely(PageUnevictable(cursor_page)))
> + Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â 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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