On Mon, 25 Oct 2010 13:12:02 +0800
Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote:
> do_migrate_range() offlines 1MB pages at one time and hence might be
> called up to 16000 times when trying to offline 16GB memory.
But size of memory section is not such big.
> It makes sense to avoid sending the costly IPIs to drain pages on all LRU for
> the 99% cases that do_migrate_range() succeeds offlining some pages.
>
did you test ? I think this patch should be tested by IBM guys.
> Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Sorry, this will HUNK. Could you wait until the end of merge window ?
> ---
> mm/memory_hotplug.c | 24 ++++++++++--------------
> 1 file changed, 10 insertions(+), 14 deletions(-)
>
> --- linux-next.orig/mm/memory_hotplug.c 2010-10-25 11:20:47.000000000 +0800
> +++ linux-next/mm/memory_hotplug.c 2010-10-25 13:07:10.000000000 +0800
> @@ -788,7 +788,7 @@ static int offline_pages(unsigned long s
> {
> unsigned long pfn, nr_pages, expire;
> long offlined_pages;
> - int ret, drain, retry_max, node;
> + int ret, retry_max, node;
> struct zone *zone;
> struct memory_notify arg;
>
> @@ -827,7 +827,6 @@ static int offline_pages(unsigned long s
>
> pfn = start_pfn;
> expire = jiffies + timeout;
> - drain = 0;
> retry_max = 5;
> repeat:
> /* start memory hot removal */
> @@ -838,34 +837,31 @@ repeat:
> if (signal_pending(current))
> goto failed_removal;
> ret = 0;
> - if (drain) {
> - lru_add_drain_all();
> - flush_scheduled_work();
this flush_scheduled_work() is removed in recent work of Tejun Heo.
> - cond_resched();
> - drain_all_pages();
> - }
> -
> 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;
> yield();
> - drain = 1;
> + lru_add_drain_all();
> + flush_scheduled_work();
This flush is unnecessary.
> + cond_resched();
> + drain_all_pages();
I think followin is better order.
drain_all_pages(); # SEND IPI and asynchronous.
lru_add_drain_pages(); # call schedule_work ony by one and it's synchronous.
cond_resched(); # may not be unnecessary (lru_add_drain_pages() will sleep.)
> goto repeat;
> }
> }
> - /* drain all zone's lru pagevec, this is asyncronous... */
> +
> + /* drain all zone's lru pagevec, this is asynchronous... */
> lru_add_drain_all();
> flush_scheduled_work();
This flush() is dropped by recent works of Tejun Heo's workqueue updates.
Bye,
-Kame
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