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Message-ID: <20120906081818.GC16231@bbox>
Date: Thu, 6 Sep 2012 17:18:18 +0900
From: Minchan Kim <minchan@...nel.org>
To: Lai Jiangshan <laijs@...fujitsu.com>
Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Andrew Morton <akpm@...ux-foundation.org>,
Michal Nazarewicz <mina86@...a86.com>,
Mel Gorman <mel@....ul.ie>,
Wen Congyang <wency@...fujitsu.com>,
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [RFC v2] memory-hotplug: remove MIGRATE_ISOLATE from
free_area->free_list
Hello Lai,
On Thu, Sep 06, 2012 at 04:14:51PM +0800, Lai Jiangshan wrote:
> On 09/06/2012 10:53 AM, Minchan Kim wrote:
> > Normally, MIGRATE_ISOLATE type is used for memory-hotplug.
> > But it's irony type because the pages isolated would exist
> > as free page in free_area->free_list[MIGRATE_ISOLATE] so people
> > can think of it as allocatable pages but it is *never* allocatable.
> > It ends up confusing NR_FREE_PAGES vmstat so it would be
> > totally not accurate so some of place which depend on such vmstat
> > could reach wrong decision by the context.
> >
> > There were already report about it.[1]
> > [1] 702d1a6e, memory-hotplug: fix kswapd looping forever problem
> >
> > Then, there was other report which is other problem.[2]
> > [2] http://www.spinics.net/lists/linux-mm/msg41251.html
> >
> > I believe it can make problems in future, too.
> > So I hope removing such irony type by another design.
> >
> > I hope this patch solves it and let's revert [1] and doesn't need [2].
> >
> > * Changelog v1
> > * Fix from Michal's many suggestion
> >
> > Cc: Michal Nazarewicz <mina86@...a86.com>
> > Cc: Mel Gorman <mel@....ul.ie>
> > Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > Cc: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
> > Cc: Wen Congyang <wency@...fujitsu.com>
> > Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> > Signed-off-by: Minchan Kim <minchan@...nel.org>
> > ---
>
> > @@ -180,30 +287,35 @@ int undo_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
> > * all pages in [start_pfn...end_pfn) must be in the same zone.
> > * zone->lock must be held before call this.
> > *
> > - * Returns 1 if all pages in the range are isolated.
> > + * Returns true if all pages in the range are isolated.
> > */
> > -static int
> > -__test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn)
> > +static bool
> > +__test_page_isolated_in_pageblock(unsigned long start_pfn, unsigned long end_pfn)
> > {
> > + unsigned long pfn, next_pfn;
> > struct page *page;
> >
> > - while (pfn < end_pfn) {
> > - if (!pfn_valid_within(pfn)) {
> > - pfn++;
> > - continue;
> > - }
> > - page = pfn_to_page(pfn);
> > - if (PageBuddy(page))
> > - pfn += 1 << page_order(page);
> > - else if (page_count(page) == 0 &&
> > - page_private(page) == MIGRATE_ISOLATE)
> > - pfn += 1;
> > - else
> > - break;
> > + list_for_each_entry(page, &isolated_pages, lru) {
>
> > + if (&page->lru == &isolated_pages)
> > + return false;
>
> what's the mean of this line?
I just copied it from Michal's code but It seem to be not needed.
I will remove it in next spin.
>
> > + pfn = page_to_pfn(page);
> > + if (pfn >= end_pfn)
> > + return false;
> > + if (pfn >= start_pfn)
> > + goto found;
> > + }
> > + return false;
> > +
> > + list_for_each_entry_continue(page, &isolated_pages, lru) {
> > + if (page_to_pfn(page) != next_pfn)
> > + return false;
>
> where is next_pfn init-ed?
by "goto found"
>
> > +found:
> > + pfn = page_to_pfn(page);
> > + next_pfn = pfn + (1UL << page_order(page));
> > + if (next_pfn >= end_pfn)
> > + return true;
> > }
> > - if (pfn < end_pfn)
> > - return 0;
> > - return 1;
> > + return false;
> > }
> >
> > int test_pages_isolated(unsigned long start_pfn, unsigned long end_pfn)
> > @@ -211,7 +323,7 @@ int test_pages_isolated(unsigned long start_pfn, unsigned long end_pfn)
> > unsigned long pfn, flags;
> > struct page *page;
> > struct zone *zone;
> > - int ret;
> > + bool ret;
> >
> > /*
> > * Note: pageblock_nr_page != MAX_ORDER. Then, chunks of free page
> > diff --git a/mm/vmstat.c b/mm/vmstat.c
> > index df7a674..bb59ff7 100644
> > --- a/mm/vmstat.c
> > +++ b/mm/vmstat.c
> > @@ -616,7 +616,6 @@ static char * const migratetype_names[MIGRATE_TYPES] = {
> > #ifdef CONFIG_CMA
> > "CMA",
> > #endif
> > - "Isolate",
> > };
> >
> > static void *frag_start(struct seq_file *m, loff_t *pos)
>
> --
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> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@...ck.org"> email@...ck.org </a>
--
Kind regards,
Minchan Kim
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