On Mon, 25 Oct 2010 10:57:03 +0800
Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote:
> On Mon, Oct 25, 2010 at 10:40:17AM +0800, KAMEZAWA Hiroyuki wrote:
> > On Mon, 25 Oct 2010 10:47:31 +0800
> > Bob Liu <lliubbo@xxxxxxxxx> wrote:
> >
> > > It's normal for isolate_lru_page() to fail at times. The failures are
> > > typically temporal and may well go away when offline_pages() retries
> > > the call. So it seems more reasonable to migrate as much as possible
> > > to increase the chance of complete success in next retry.
> > >
> > > This patch remove page_count() check and remove putback_lru_pages() and
> > > call migrate_pages() regardless of not_managed to reduce failure as much
> > > as possible.
> > >
> > > Signed-off-by: Bob Liu <lliubbo@xxxxxxxxx>
> >
> > -EBUSY should be returned.
>
> It does return -EBUSY when ALL pages cannot be isolated from LRU (or
> is non-LRU pages at all). That means offline_pages() will repeat calls
> to do_migrate_range() as fast as possible as long as it can make
> progress.
>
I read the patch wrong ? "ret = -EBUSY" is dropped and "ret" will be
0 or just a return code of migrate_page().
> Is that behavior good enough? It does need some comment for this
> non-obvious return value.
>
> btw, the caller side code can be simplified (no behavior change).
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index dd186c1..606d358 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -848,17 +848,13 @@ repeat:
> pfn = scan_lru_pages(start_pfn, end_pfn);
> if (pfn) { /* We have page on LRU */
> ret = do_migrate_range(pfn, end_pfn);
> - if (!ret) {
> - drain = 1;
> - goto repeat;
> - } else {
> - if (ret < 0)
> - if (--retry_max == 0)
> - goto failed_removal;
> + if (ret < 0) {
> + if (--retry_max <= 0)
> + goto failed_removal;
> yield();
> - drain = 1;
> - goto repeat;
> }
> + drain = 1;
> + goto repeat;
> }
This changes behavior.
This "ret" can be > 0 because migrate_page()'s return code is
"Return: Number of pages not migrated or error code."
Then,
ret < 0 ===> maybe ebusy
ret > 0 ===> some pages are not migrated. maybe PG_writeback or some
ret == 0 ===> ok, all condition green. try next chunk soon.
Then, I added "yield()" and --retrym_max for !ret cases.
Thanks,
-Kame
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